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Ok, this might end up being a short thread, or maybe not but here we go. Ever since getting my car running (after sitting in a field for 16 years) which at this point is about two years ago, I have had this annoying 'bump' or misfire at idle and low rpm - it might be present at higher rpm but it's not noticeable at all, at least under load - that has proven untunable to remove. In these past couple years the car has seen many carb setups, three alternators/a bunch of wire tidying, multiple dizzy's, normal maintenance items, a DLIDFIS install, and as of recently a new engine. The only two major things I have not changed/replaced (and I know I'm about to get some ridicule about this first one) are the plug wires and the fuel pump. Oh, and I should mention that this is a 1980 RX-7, but by this point I doubt that will be of much use since so much has been modified. Anyway, I guess this post is to see if any of you folks have run into an issue similar to this before. Perhaps ironically, my bets are most definitely on either the plug wires or the pump (the pump will be getting replaced soon as I know it is causing other issues). The plug wires passed the 'check the resistance' test and that's about as far as I've gotten there (and I did that a while ago). So yeah, by now I really should have replaced the wires and I don't know why I haven't done it already... I'll attach a couple recordings of the exhaust and engine bay sounds here in a second, but I suppose the other reason for this thread will be for anyone in the future who is running into the same issues (not carb related as many of the other misfire threads are) - a testament to covering the basics.
To sum up that unnecessarily long tangent, has anyone run into an issue like this before and what was your solution? Sometime soon here I'll pick up some new wires, but for the time being I'd just appreciate some minds on the matter. Going along with the plug wires, who has a favorite brand or product line they like to run; recommendations for a modified street car? Do note that I believe these wires were replaced at some point (they're the blue NGK oem style ones) but who knows how long ago that was.
Here's a few audio clips (note the location of the recording in the file name):
How are you running stock type NGK wires on a DLIDFIS install,or have you removed that and gone back to original J109 igniters/ignition. For a mostly stock ignition system,NGK wires work good and cost@$15. Noted you resistance tested wires,what were the values?
You could have broken down wire jacketing on coil/plug wires. If this were the case,opening hood while dark out with engine running,wire jacketing leaks could be seen jumping to ground. Don't overlook secondary towers on ignition coils bleeding secondry KVs to primary terminal(s) or to mounting bracket. Have you ohmtested coils?
With engine running,spritz coils,cap,wires with a spray bottle of water,rev engine hard to load ignition system. You can add @10% blue windshield washer fluid to mostly full spray bottle and retest. Where spark is jumping to ground that you cannot hear/see,the weak mixture of alcohol will partially ignite and go out quickly so you can respray that area a 2nd time to duplicate problem. It looks like a faint greenish blue spark,kind of like St. Elmos fire.
How am I running the stock style NGK wires with DLIDFIS? Quite simple, I didn't purchase new wires because I thought the old ones checked out fine - likely a mistake... Why beyond that? Well that's a very good question that I do not have an answer to. That said, yes, I am still running a DLIDFIS setup and I should have replaced the wires at the time of the conversion. It was a while ago that I tested the wires so I'd have to go back and redo that for the numbers - I should be able to get that done tomorrow I think.
You know what, while I have never seen any sparks where they shouldn't be, I can't say that I've looked particularly hard. I have however noted a clicking sound (like that of an electric arc) coming from either the trailing coil or something else in/near the ignition system. I first noticed this back before I went direct fire, and it seemed that even when swapping out coils, the sound remained. So far I haven't paid close enough attention to whether these clicks coincide with the misfires, although if I recall correctly they were rather sporadic yet often in occurrence. I can check for breaks via your suggested method sometime in the next day or so. Unfortunately I will not be able to rev the engine hard due to err... uh... noise complications... I might get a couple rounds in before the neighbors start getting a little peeved, we'll see.
Oh, and the coils checked out last time I tested them. Right now I'm running a stock coil for trailing and two MSD High Vibration Blaster Coils for the leading side (same as the normal MSD Blaster coils but with an epoxy potting so they are more resistant to vibration and can be mounted in any orientation; PN 8222).
How are you running stock type NGK wires on a DLIDFIS install,or have you removed that and gone back to original J109 igniters/ignition. For a mostly stock ignition system,NGK wires work good and cost@$15. Noted you resistance tested wires,what were the values?
You could have broken down wire jacketing on coil/plug wires. If this were the case,opening hood while dark out with engine running,wire jacketing leaks could be seen jumping to ground. Don't overlook secondary towers on ignition coils bleeding secondry KVs to primary terminal(s) or to mounting bracket. Have you ohmtested coils?
With engine running,spritz coils,cap,wires with a spray bottle of water,rev engine hard to load ignition system. You can add @10% blue windshield washer fluid to mostly full spray bottle and retest. Where spark is jumping to ground that you cannot hear/see,the weak mixture of alcohol will partially ignite and go out quickly so you can respray that area a 2nd time to duplicate problem. It looks like a faint greenish blue spark,kind of like St. Elmos fire.
So,you have both leading coil output wires going to their respective plugs? You’re running trailing ignition thru distributor?
Did you switch trailing coil/plug wires to leading positions on distributor cap to take advantage of the lesser gap for spark to jump so more spark energy goes to trailing plugs?
What plugs in engine,should be BR8EQ14.
Do you have engine running centrifugal advance only or running vacuum advance on leading/trailing ignition?
Do you know if centrifugal advance is working and how much it actually advances,ever check?
Ignition timing is base+centrifugal+ vacuum advance and should be checked in that order to determine total advance.
Listen closely at Distributor cap for sound of clicking/ticking,inspect terminals in cap and rotor for wear and arc marks.
Look at carbon buttons in top of cap closely for burn marks. How old is cap and rotor?
Look closely in distributor cap for carbon tracking from one terminal to another,same for rotor.
If age of these parts is not known,replace them.
It would surprise many people that the “fix” for driveability problems is no more than making sure your ignition system is solid.
What type ignition modules are you using,are you running all coils/modules from original wiring from ignition switch for power source?
Yes, both leading coils are running directly to their plugs. Correct, the trailing is running through the dizzy.
The trailing is indeed running through the leading portion of the dizzy for the reason you mentioned.
Yes, the plugs are BR8EQ-14's
I did once check mechanical advance and it worked fine. This was right after swapping in my restored 1982 dizzy. Vacuum advance also works correctly. Total advance was checked and set on the previous engine, but not on this new one yet.
I will do so when I work on it today.
The cap and rotor were replaced less than a year ago I believe.
Could you restate the carbon tracking bit? I'm not quite sure what you want me to look for there.
Ignition modules are DR-100 HEI module's for leading, and trailing is still the stock J-109 that I tested to ensure was operational before installing it. I do have a couple other working J-109's that I could try, but considering that this issue has remained across this dizzy and other's I feel like that is less likely, though I can still test it if you think it'd be worth a shot. The original power source is now used as a trigger for a relay that supplies power to all ignition components (except maybe the trailing coil, I'll have to check) directly from the battery.
Carbon tracking is just that,most common inside distributor caps,can be found on secondary coil towers and occasionally on porcelain of spark plugs,from leaky plug/coil wire boots.
A carbon track looks like a lead pencil tracing,often with jagged edges-like a lightning bolt.
It is the path to least resistance for high KVs of voltage looking for a place to go due to high plug firing voltages caused by:fouled/incorrect plugs/improperly gapped plugs,high resistance in secondary ignition system,wires,large air gap between dist terminals and rotor and spark plugs-worn out parts.
It can be caused by water/condensation inside dist cap that voltage starts using to find least resistance/ground.
Once this particular path has been used by high current more than a few times,it develops a somewhat defined ridge of carbon on inside cap surface going from terminal to terminal and/or to ground.
The track stays there-like a road not being used- til current values are very high again,at which point current is bled from original terminals in cap? to another terminal or to ground.
A bright light and studying around cap terminals to each other and to base of cap closely,rarely inside a cap will a carbon track be found in a straight line.
Sometimes track can be cleaned out with a cloth and WD-40,but this is not the norm and replacement is needed.
Don’t confuse patterns cast into plastic of distributor cap for carbon tracks,a carbon track can sometimes be felt with a fingernail though these will be well established and seen by eye 1st.
Example,once doing a deep water crossing with my truck,I had water up onto intake manifold and base of distributor but no higher. All the steam from hot manifolds/engine parts coming into contact with water condensatef on outsideinside of dist cap and wires and a misfire soon developed.
I pulled off cap and sprayed out with WD-40-WD stands for water displacing- wiped out cap and dried out wires and went on my way. By time I got home I had a hiccup on light acceleration and idle. While cleaning cap got me home,it still had to be replaced to get rid of the hiccups.
Better quality dist caps seem to suffer tracking less than cheaper ones,but not immune to it.
As far as J109 and causing misfire,may not be likely cause for it as you make no mention of tach issues or fuel pump not running(though you did post that you were replacing it for some issue). Never say never but you can isolate the two ignition systems by disconnecting trailing input to module. Car will run on leading only for several minutes. If hiccup subsided problem will be associated with trailing ignition.
Possible to post pics of your DLIDFIS system showing wiring from distributor to modules/coils?
Ok that makes sense. Thank you for that explanation, I will look for that when I do some other work this afternoon.
I actually have had tach issues, but they are separate from the ignition and are rather at the fault of the gauge cluster (I've got some weird ground issues with it that only show up every once in a while). But like I just said, that's a separate issue. Since this is a 1980 the fuel pump isn't connected to the trailing coil so that wouldn't manifest as a sign either. In fact, the tach normally would run on the leading for a stock 1980 ignition system, but for DLIDFIS I swapped it over to trailing for simplicity.
I took a couple shots of the wiring so I'll attach those below. I also confirmed that the trailing is powered from its original wire so that's something to note. This afternoon I'll try running the car without trailing to see if that alleviates the problem like you suggested.
In the photos you'll probably notice the close proximity of the plug wires to the signal wires. I have tried moving the two apart to see if that solves the issue but there was no noticeable change at all. Just something to note.
A lot of people change fuel pump wiring,particularly for running larger pumps with more current needs,didn't know what you had.
I would remove that ground wire you have twisted into harness from distributor at leading igniter mounting screw and terminating at relay mounting point. It has no value and may/may not be a cause for weird problem you're having at idle speed. The distributor body is grounded to engine and engine assembly grounded to chassis.
The signal/frequency/voltage generated by pick up coils,particularly at low engine rpm is very small (.2-.3 volts) and doesn't take much to corrupt it in the distance it has to run. Even if your ground is meant as a shield,being connected at both ends negates any benefits. A shield wire is not meant to be twisted into signal harness,more meant to be overlaid in some type of sheath and grounded at one end. Twisted wire pickup coil harness is fine by itself as long as not routed too close to alternator output wires,plug,coil wires. Other than that your wiring looks pretty solid. Coil/plug wires look to be in good condition,should still test them.
Have you yet tried to minimize the bump at idle speed by adjusting idle fuel mixture?
Speaking of changing fuel pump wiring, I did that just yesterday (perhaps you saw the post in "What did you do to your FB today?"). But anyway, that's beside the point.
The ground wire was actually added after the fact as a 'shield'. Yeah, I know it's not the right way to do it - I was hoping I could find some of that woven metallic sheathing like Mazda used for the '80 electronic dizzy, but alas, I didn't find a cheap or local alternative - so I figured I'd just give it a shot. It is only grounded on the one end and after adding it I noticed no differences. I could pull it out if you still think I ought to.
Didn't find any signs of carbon tracking anywhere, and I ran the car without trailing and the issue persisted so... some more things to note.
I retested the plug wires today and they ranged from 4.0-4.5k ohms. I found spec as 16k ohms +/- 40% so their off a good bit, but considering these aren't the 'factory' wires, I have no clue what the true spec is. I didn't notice any tears or anything, or internal breaking for that matter when testing them. I'll still do that spray bottle test, though it will have to be tomorrow or sunday. I might just replace them for peace of mind anyhow, we'll see. I've been doing some looking and it seems that the Taylor Spiro-Pro Universal sets are well regarded and won't break the bank. They're a 'performance' 8mm wire, but I don't see a need for anything more. I'm ordering some parts from Summit anyways so I might as well do them now as well.
I have tried to reduce the bump via the idle speed and mixture screws but to no avail. I'm going to check into the carb again maybe tomorrow - the misfire issue has gotten more pronounced with this new engine (only difference is the slightly extended closing '74 spec intake and slightly earlier closing T2 exhaust ports), although as I said before, this issue has remained across multiple carbs, dizzy's, engines, etc... Oh, you know what, this engine also has the lighter '82 year flywheel compared to the 83-85 (not actually sure which year it was) engine/flywheel that was originally installed. That's probably helping to bring the misfire out a little bit.
The reason for replacing the fuel pump is that it's not, and hasn't been (even on the old engine with a stock carb), keeping up. Even holding at 3-4k rpm under no load the fuel level drops a noticeable amount in the fuel bowls (fuel filter was replaced recently and is still clear, and I've dropped the tank before to reseal it so I know the lines are fine too). I also did some more free rev testing yesterday and I noted that the 'bump' is present even at higher rpm's when holding steady - at least up to 5k which is as high as I got before stopping.
Along with the other things I said I'd check tomorrow or sunday, I think I'll also take a look at the PCV and any other vac lines that remain since that's something else that hasn't changed all this time. I have a spare PCV or two in storage, so I'll give those a shot and see if they change anything. Other than that and what I mentioned above I can't think of much else that might be messing with stuff - again, keeping in mind that this issue has remained to some extent across many different part combinations. Anything I might still be missing?
Edit: I should mention that I cleaned those plug wires quite thoroughly back when I first started this project. They sure didn't look that nice before that and, although I doubt I damaged them in the process of cleaning, I may have. Didn't show up in the testing if I did though.
Last edited by Benjamin4456; 07-05-19 at 10:50 PM.
Ok, I ordered my fuel pump components and new plug wires both of which should be here within a week or so (the pump parts should get here sooner than the wires though).
With that said, I did some more testing today and I didn't make any real progress. I took the carb apart again and all seemed well, or actually not quite well, but they were things that were not causing my issues. Essentially my mechanical secondary linkage had worked its way loose so I fixed that and I also swapped back in my 92 primary jets after trying some 93's for a day with no good changes. The 93's decreased throttle response slightly and made the car easier to stall from a stop but that was about it. Note that that change was accompanied by raising the float a hair (they were below the midline on the sights - I expect I'll have to change them back when I get the new pump but I've done float adjustments plenty of times so I'm pretty used to it, but regardless, I did end up doing two things that made the carb richer. This did however make the idle slightly less bumpy, but slightly less if even and it was probably due to something else. But like I said, I swapped back in the 92's (but left the float alone this time) and we're basically back to square one. Although now I'm idling back down at 500ish rpm with lights on - which I personally like even though it's probably worse for my engine mounts - which I couldn't do before all this 'work' so I guess that's a positive note.
Anywho, the PCV is fine as well as all the other remaining vac lines - no leaks. I checked the brake booster with the ether test, as well as the engine bay in general and no changes. So there don't appear to be any vac leaks which is good I suppose; would have been an easy fix though. Here's something else to note though, right now my mixture screw is about two turns out and is really touchy. Now, that's probably due to the mods I've done (most notably the 120 primary no. 2 air bleeds), but again, this issue has persisted across many carbs so I really don't know if that info is worth much. I'm really curious what changing my fuel pump and plug wires will do, if anything. I just can't think of anything else that might be causing this. Is there some way electrical noise (besides in the ignition system) or just the old wiring might be causing this. I guess if there was a broken wire somewhere that would mess with stuff, but there are so few wires left on my engine that are original... I don't know. Realistically this is a minor issue - the car 'runs' and drives just fine - it's simply annoying that I can't figure this out. If the wires and pump don't solve things I'll be at a loss. If anyone has any ideas here, do share. Although remember, this has been an ongoing issue across many different parts (see the first post for everything that's been changed).
Man, that got a little down by the end. Anyway, thanks for the advice. Hope we can get this issue solved .
Finished installing the fuel pump this morning and I've got to admit, the idle 'bump' has indeed improved. I can't say it's much easier to cold start the car like I was hoping (the old pump wouldn't keep up at all when cold) but driving around it's a good lot smoother and I'm definitely happy with the install. It's a bit noisier than I had expected but you only hear it at idle, and once you're cruising at anything above 25 it gets drowned out by road noise and the like. For reference it's a Carter 4070 with a Summit Racing regulator and gauge. Here's a couple of shots of the install:
Plug wires arrived today too so tomorrow I'll get those cut, assembled, and installed. Hopefully they will further improve the situation but we'll see. If not it's got to be down to fine tuning the carb or, who knows, something else... I should check and readjust the floats again now that I'm not compensating for a failing pump too. Fuel pressure is set at 2.5psi. I'll update again after the wires are installed.
Well I've gotta say, those wires didn't improve much, but they sure look good and offer some peace of mind. That said, I assembled and installed the new wires yesterday and everything went quite smoothly. I also installed some new spark plugs (at the time of my rebuild no store could get them soon enough, and there were also order issues). Anyway, I tested first with just the new wires and as I said above, there was no real difference. However, after installing the new spark plugs the idle was definitely smoother. So far I'd say that the pump had the greatest effect, plugs following it, and then finally the wires as the least affecting. Speaking of fuel pump, the car pulls hard now in the top end. It's seriously impressive the difference the new fuel pump made in power - I sure must have been running dry up top, or actually I know I was, but it's crazy to see how much I was missing.
So anyway, the misfire issue still persists slightly; once again it's most noticable when there is no load on the engine. Right now I'm staying somewhere that I don't have a level work area so I can't check/fix the floats yet but when I get a chance I will. At this point the remaining glitch has got to be down to the carb tuning surely...? Can't think of anything else. Suggestion concerning that or otherwise are of course welcome.
Oh, here's a couple photos of the plug wires; Taylor Spiro-Pro Universal Wire Kit - 135 degree boots - for reference.
Yeah,i'd remove that ground wire you have in leading harness from dist to bracket on fender. Can't say without a doubt it's causing your bump issue,however it's not doing what you intended for it to do.
Couple more suggestions...
Check the airgap on both leading and trailing ignition pick up coils to reluctor. Necessary to use brass feeler gauges so as not to magnetize reluctor. Mazda gives test specs in FSM for .023-.035 for airgap measurements. I have found occasionally on hard to start cars,carbed and FI,when everything else was ruled out,to scope and compare each generated signal with the other.Good place to test next when other checks of ignition system have showed no flaws.
Ability to see the signal pattern developed and voltage peaks on each side of sine wave can further isolate possible problems with generated spark quality that could contribute to misfires. If there is a perceptible difference in signal/voltage generated,next thing is to pull cap/rotor/shield and rotate engine by hand until reluctor tip is exactly aligned to middle of magnet on pickup and measure airgap,next do the other pickup coil and compare them. They should be essentially the same distance,if not,adjust the lesser gap to the measurement of the larger within above checking measurements.Checking resistance of windings in pickup coils is next while inside distributor. Disconnect the inner connector from igniter and ohm test coil. The exact reading is not important as the reading will change with temperature. What is important is that resistance specs on both are identical.While pickup coils are known to seldom fail,after all these years,it's possible they get banged around a bit,like dropping a distributor...
Consider changing leading ignition wiring from dist to module to thinner gauge(18 gauge). I think it helps to preserve integrity of low voltage signal better in a long run than the thicker wires do to get a cleaner signal to modules.
When i was bench testing final selection of parts for the DFI system i installed on my car using a spare FB distributor,motorcycle battery,jumper wires,spark plug type spark testers with no side terminals that force generated spark to jump from center porcelain to edge of plug housing,a 2nd gen leading ignition coil and a hi output Ford TFI ignition coil. High amp HEI ignition modules. I chose the ignition coils and modules after testing stock diamonds,an ACCEL super coil,MSD blaster coils,the 2nd gen and TFI coil. I tested J109,standard HEI module,hi amp HEI module and switched all components around to test each with all other components.
I was able to test both leading and trailing simultaneously and observe quality/color/power of spark generated. One of the 1st things noticed was generated leading spark was noticeably stronger than trailing spark-no matter what ignition components were swapped around. All the components put out a stronger spark on leading pickup coil. I was spinning shaft on distributor by hand for this portion of tests.
I then put a dual trace labscope on both pickup coils and spun dist by hand and by corded drill and 1/4" collet hi speed air tool . I could see signal pattern and peak voltage developed by both pickups and trailing pickup pattern was different from leading which had a cleaner sine wave and a higher peak voltage at hand spinning speed which i "guessed"was about cranking speed and chucked in a drill that i guess spun at @ 800-900 rpm and hi speed air tool that spun dist @? 3k-5k rpm. Not lab scientific standards,but repeatable testing.
The leading pickup voltage generated at hand speed was .2 volts,trailing was .15 volts. Drill speed was .5 and .3 volts respectively. Air tool speed was 2.3 and 1.9 volts respectively. Signal generated by leading coil was noticeably cleaner with well defined sine,trailing a little ratty less defined,lower voltage-enough to trigger module but not as cleanly as leading was doing.
At this point i chucked dist in plastic jaw faces in bench vise and looked closely at pickups,it was subtle but the trailing pickup coil was misaligned/bracket bent. I straightened mounting bracket by eye to where both pickups looked identical and measured air gaps on both.
Leading was .028 trailing was .022. I carefully bent trailing coil to match the .028 of leading. Hooking up labscope to dist and repeating all three spinning tests the signals were identical and voltages generated the same. Next hooked distributor up to modules,coils and retested for spark quality. Both looked the same,switching components no difference. Before i went to sleep that night i was running all this thru my mind and wondered if manipulating airgaps would alter ignition coil out put.....next evening i started playing around with different airgaps to see if generated spark quality/color/power changed.
Very tedious,time consuming,there were results. I settled on .032 airgap for both pickups and found this to be best combination for best signal pattern/voltage. Wider gaps would degrade signal as would narrower gaps.
Starting with J109 there was perceptible color improvement,sound of spark. This was more noticeable with standard HEI module and really noticeable with hi amp HEI modules and 2nd gen and TFI coil. The color of spark was bright blue/purple and each spark event at hand spin speed had a loud snap as it jumped gap on spark tester-even with not spinning the dist shaft too fast by hand spark was stronger than before. Air tool speed sounded very much like a mig welder,nasty,good strong spark. What began as @1/2 hour bench test of ignition components turned into 3 evenings of experimenting,lol. But i learned some things from it. I believe manipulating airgaps for best signal/voltage changes dwell times? in hi amp modules and more fully saturates ignition coils for a more powerful spark.
I set gaps in dist in my car to .032 and assembled all DFI components and installed,made up plug wires with MSD 50 ohms a foot 8.5mm wires,transferred trailing ignition wires in cap to leading position. 1st time car started faster and idle sound was different,driving,it's noticeable when 5th,6th ports open,the exhaust tone gets raspy even with partial throttle and it pulls hard up to and past the buzzer. Much more noticeable torque in low rpm range. The DFI mod and RB streetport exhaust really work well together and best mods i've done to enhance driveability and power. I've since switched to Nippondenso RX8 racing plugs which are not cheap,for leading and oe NGK BUR8EQ14 for trailing and performance improved a tick. For a mechanically stock 140k mile engine runs well,enough to be fun.
Very interesting good sir. I will pull out that 'shield' wire next chance I get, and I will also test the air gaps and inspect things in the dizzy closer than I did before. Unfortunately that won't be able to happen that soon though as I'm away from home for the time being.
I'm curious as to what your results were with the blaster coils and the normal HEI modules compared to your preferred/final setup - those are what I'm running. The wires I just purchased are rated at 350 ohm's per foot; sounds like you're running "super conductors".
I believe my pickup wires are 16 gauge at the moment, and unless you feel it is quite important, I don't really feel like redoing them for that small change, at least now. Even if I were to redo them, it couldn't be anytime soon as I mentioned before.
Thank you for that info. I'll continue to update this as/when I make progress.
Something quick, but I've been noticing lately that I get a lot of bucking (much more than I used to, or at least at a higher rpm than I used to) when decelerating. Before the engine swap it commonly started at or slightly below 2k, although now it begins even as high as 3k. I figure this is due in some part to the porting, but it might be something to note otherwise. I've found in the past that bucking on deceleration can be manipulated with slight changes in the idle mixture, but so far that has yet to do anything this time around.
I still haven't got a chance to look into things much, but I might be able to get hold of a few tools today and do some poking around, we'll see. At the very least I'll do some visual inspection if I can't pin down some tools.
So by this point, the title of this thread is no longer accurate. Rather, this misfire is present across most if not all of the rpm range under a no or light load scenario - although it does improve just slightly when above idle. I finally got the float levels set correctly yesterday as they were a fair bit too low. For whatever reason I had to set them to 13.75mm (with a used air horn gasket) to get them in the middle of the sight glass, perhaps it's because I'm using SA floats with FB needles and seats, who knows. Anyway, that didn't change the misfire but it did improve drivability somewhat, particularly when starting from a stop. Further adjustments to the mixture screw also did nothing besides make it worse either direction. I also pulled out that extra wire from the pick-up wire loom and that didn't change anything noticeably either.
I did some quick inspection of the dizzy, but the friend I was going to borrow a set of brass feeler gauges from is out of town so that still has to wait. I'm back to the point where I really don't know what could be causing it if I don't find anything askew in the dizzy. Unfortunately I have no access to an oscilloscope or similar so that's not something I can check either. Is there anything else that would cause a misfire like this, likely or not?
Ok, I did some inspection yesterday and while there was nothing that stood out as a major issue, here's what I found.
- I confirmed that vacuum and mechanical advance is working - visually; it's pretty neat how you can pull off the dizzy cap when running DFI and see all the moving parts do their thing.
- There was a little more slop in the leading vac advance mechanism than seemed normal, but after comparing it to another dizzy it's not much worse in comparison.
- Timing is good.
- Gap between reluctor wheel and pickup is about 0.030" for both leading and trailing. Being that it's quite close to what you stated as the optimum GSLSEforme, I didn't find it necessary to change, although I also didn't see a good way to adjust it. Where on the bracket were you bending it? If I need to adjust one in the future I'd like to avoid breakage so if you have any pointers there, do share.
Lastly I pulled the dizzy and spun it by hand with only the leading components hooked up and I got consistent, strong purple sparks even at hand spinning speed. I ended up wrapping a string around the gear to use as a pull cord and even then there seemed to be nothing amiss on either plug (both were connected at the same time).
So I'm back to not knowing where to look again. If the misfire detailed somewhere above sounds like something familiar to anyone - maybe it is fuling relating, who knows - please feel free to chime in. I'd also like to note one last thing for the time being: on hot starts the misfire only develops after maybe 5-10 seconds of idling, if that points to anything.
Do a compression test,preferably with a rotary engine compression tester. it will give you exact,repeatable information that a regular compression tester cannot. Aware it's a low miles engine,you have made adjustments/changes/upgrades to fuel,ignition system,each affecting your misfire in some way,diminishing it slightly but not cancelling it out.
It is possible to see the event by scoping ignition,it may be a random misfire in both rotors but since there's three bathtubs in each rotor,the best way to see which bathtub(s) are the offender(s) is proper compression test. If you've ruled out fuel/ignition as potential causes,testing for mechanical deficiencies is the next step in diag process.
Quick post, but I did a compression test last night when I got home, so here's the results:
Rear @ 274 rpm:
- Face 1: 107 psi
- Face 2: 108 psi
- Face 3: 106 psi
Front @ 269 rpm:
- Face 1: 109 psi
- Face 2: 110 psi
- Face 3: 108 psi
So while perhaps a little low (after doing the test I noticed the probe's o-ring looked slightly torn so that may be why; I could replace it and check again if need be) everything seems pretty consistent. This was done right after I got back from about 12 miles of highway driving.
And yeah, it'd be nice if I could find a scope. I'll keep looking to borrow one or see if a local shop has one I could use, but I doubt it.
Ok, I reinstalled an essentially stock 82 carb (only missing the no. 2 anti-afterburn valve but that's not directly carb related anyway) and guess what, it still misfires. Now it's not as bad as my performance minded Nikki, but I believe that's mostly because I have the idle set much higher than I did on the other carb (~950 vs ~580) - when I lowered it a little the misfire became more apparent. What has been most noticeably reduced is the repetitive nature of the misfire, although sometimes it still manifests itself in that way. I have, however, noticed a couple negatives thus far with this carb compared to the previous one. For one, if I hold a free rev at really any rpm I get much worse misfires than I did on the other carb. Not undrivable, but I can feel it while cruising as slight lurching which I believe is usually attributed to too lean of an idle mixture - right now I have the mixture set a little over half a turn richer than hunting. Additionally, on decel the bucking is slightly worse than my modded carb too, although once again that's usually due, at least in part, to a lean idle mixture from my experience. My issue right now is that if I make the mixture richer, the idle misfire worsens (it becomes more cyclical, sort of hunting-like, which my other carb would do too) and the cruising misfire doesn't change much at all. Decel bucking improved slightly with the mixture change, but I deemed a better idle worth more than some bucking under ~3k and therefore I reverted it. So is this giving anyone ideas? I'm still confused as all get out by this since it seems like nothing I do improves the scenario by much. All theory's welcome.
Here's something else that might be noteworthy. When going to start the car, quite often there is a 'burping' sound that comes from the fuel system that lasts anywhere from 5 to 20+ seconds. It's most apparent on hot days/hot starts, although it also sometimes happens if the car has sat for over a day. Before the new fuel pump, there was no 'burping' sound, but I could hear air running through the fuel lines almost every time I went to start the car regardless of weather or when it was last run - unless it was shut off less than 10 minutes previous or something. The filter is, and has been, clear of debris - it's see-through. Something else fueling related that I've noticed is that with misfires comes sporadic activity on my fpg. I'm guessing that it's simply due to the extra vibrations of the misfires getting transferred to the gauge which is mounted on the firewall, although perhaps it's not. Maybe air is ending up in the lines randomly - perhaps due to cavitation from a partially blocked tank pick-up line, although it was clear last time I checked - which is causing the jumpy needle, who knows. At this point I'm just thinking out loud here. I'm still looking at the possibility of borrowing a scope to check out the ignition, but I haven't made any progress there as of yet.
Edit: I've also noticed that the speed/load of the pump (noticed per its sound) doesn't stay constant even if the car isn't running and no other accessories are on that might cause power cycling. It's also directly powered from the battery though a relay, so it should be getting a fairly consistent power supply, particularly when the car is off (the stock computer has been completely disconnected so it couldn't be messing with things). The only components that might lead to slight fluctuations in power distribution would be my stereo (the pump fluctuates even if the radio is off), my subwoofer (trigger on by stereo) and maybe something in/related to the dash. Of course the pump also varies when the car is running too, but perhaps that is another pointer? Maybe another sign of vapour in the system? I could also just be over thinking things. Thoughts?
Edit 2: I believe I've already mentioned this, but I'll say it once again because I noticed it many times over the past couple days. Particularly on hot starts, the misfire does not manifest right after starting the car. I say hot starts because that's the only time I can start the car and it doesn't require either choke, fast idle, or throttle pedal manipulation. After starting the car it will idle beautifully anywhere from three to ten seconds before the misfire begins to develop again. During this period of time the idle is also slightly lower than what is normal (slightly, not by much but it's audible). Then rather suddenly, although smoothly, and without apparent reason the idle will pick up to normal and then begins the misfire once again. I don't have the hot start assist hooked up anymore - and haven't for a while - so nothing other myself would be messing with the throttle. There's also no smog equipment other than the PCV so... once again, perhaps another pointer.
Last edited by Benjamin4456; 08-11-19 at 03:58 PM.
From your statements,it sounds like your fuel system is losing its prime. You could have a pinhole in fuel supply or return line somewhere. The pinhole would be at the top of the line where fuel wouldn't leak out but air can be pulled in. Often can be found on the supply part of system between tank and fuel pump but not necessarily.
You should not be hearing air in lines when turning key on and pump begins to run. If the car sat for a year i could see system losing its prime and pump having to fill fuel system,but that should not happen a 1/2 hour after car is turned off and restarted or any other time up to car sitting for couple days and pump taking several seconds to bring system up to pressure. There should be no air in the fuel lines on a "tight"system,not in 10 minutes,1/2 hour,an hour,2 hours,you get the idea. Accept you have a leak somewhere in your fuel system.
If this were an older car with a mechanical fuel pump you would be cranking the engine for a long time for the pump to pull fuel from tank up to front of car and fill carb bowl(s) to allow engine to start.
Are you running a return line to the tank from fuel pressure regulator? What is the fuel pressure when engine is running? How long does gauge hold pressure after key is turned off? What happens when you immediately crank the car as soon as you turn the key on after it has sat for hours,overnight. Does it start right up?
Where to begin? Let the car sit for a day,take air cleaner off and verify front and rear carb bowls are at normal 1/2 way up windows in both fuel bowls. Look at fuel filter at back of car,is it full of fuel? It should be
Put a voltmeter across power and ground wires at fuel pump. Do you have access to a clamp on ammeter? If you do,clamp it around power wire of fuel pump. Watch what the voltage and amp readings do when you turn key on,they should be steady-no matter what pump is doing. Do the readings change when the pump picks up fuel,what happens? Leave key on for a couple minutes and observe for pump fluctuation and volt/amp readings. Post back what you find.
I have a 74 four port 13b with some additional porting/polish. It has a DHLA 48 and long primary exhaust. I have been chasing a similar sounding problem. After checking and adjusting just about everything its better but still present. I kinda think its the nature of the beast... Overlap, No vac advance, Light flywheel, Carb etc... Runs great everywhere else and pulls to 8K.
Yo say it started easily when cold and runs fine with no choke or throttle input until it warms up a little bit. That is a sign of a rich condition at idle. It is perfectly tuned for cold running but as soon as things warm up, it begins to run rough due to being too rich for warm running. Does that make sense? Is that what it's doing? Or did I read you wrong?
From your statements,it sounds like your fuel system is losing its prime. You could have a pinhole in fuel supply or return line somewhere. The pinhole would be at the top of the line where fuel wouldn't leak out but air can be pulled in. Often can be found on the supply part of system between tank and fuel pump but not necessarily.
You should not be hearing air in lines when turning key on and pump begins to run. If the car sat for a year i could see system losing its prime and pump having to fill fuel system,but that should not happen a 1/2 hour after car is turned off and restarted or any other time up to car sitting for couple days and pump taking several seconds to bring system up to pressure. There should be no air in the fuel lines on a "tight"system,not in 10 minutes,1/2 hour,an hour,2 hours,you get the idea. Accept you have a leak somewhere in your fuel system.
If this were an older car with a mechanical fuel pump you would be cranking the engine for a long time for the pump to pull fuel from tank up to front of car and fill carb bowl(s) to allow engine to start.
Are you running a return line to the tank from fuel pressure regulator? What is the fuel pressure when engine is running? How long does gauge hold pressure after key is turned off? What happens when you immediately crank the car as soon as you turn the key on after it has sat for hours,overnight. Does it start right up?
Where to begin? Let the car sit for a day,take air cleaner off and verify front and rear carb bowls are at normal 1/2 way up windows in both fuel bowls. Look at fuel filter at back of car,is it full of fuel? It should be
Put a voltmeter across power and ground wires at fuel pump. Do you have access to a clamp on ammeter? If you do,clamp it around power wire of fuel pump. Watch what the voltage and amp readings do when you turn key on,they should be steady-no matter what pump is doing. Do the readings change when the pump picks up fuel,what happens? Leave key on for a couple minutes and observe for pump fluctuation and volt/amp readings. Post back what you find.
Perhaps that's why with my old stock pump after doing fuel system work it would take so long to start moving fuel, hmmm...
I'm running a returnless regulator and using the Nikki's stock return line (you can see most of the set up in post #11). I have the fuel pressure set at 2.5psi but it bounces around a bit when the engine is running. I'll check if the bounce is due to vibrations by removing it from the firewall when I do the other tests. The gauge does not hold pressure when the key is off, although that would make sense seeing as how I'm running a post-regulator return, yeah? After sitting overnight and cranking immediately (choke **** pulled out on this stock carb) it spins for a little while before catching, just a few seconds though.
After sitting for about 18 hours the fuel was at the bottom of the sight glass on both bowls. I checked the filter yesterday after returning from a drive (didn't shut off the car) and the filter was less than half full of fuel. I've seen it full a few times, but not often.
I might get to the power checks this weekend or mid next week - a bit busy for now. I do have clamp style terminals for my multimeter.
Thanks for the pointers. I'll do the tests next chance I get.
07-03-19, 07:54 PM
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