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I've been doing a good deal of carb work lately - most of it pertaining to idle adjustments - and there's been a few recurring issues I've run into so today I finally checked out the ignition system (again). Turns out there's some weird stuff going on.
Firstly here's the setup I'm running:
- DLIDFIS
- gutted ignitor for pickups
- 16 gauge wire running from the pickups to the ignitors
- 12 gauge wire used elsewhere
- GM HEI ignition modules (DR-100)
- Taylor Spiro-Pro 8mm plug wires
- BUR7EQP in leading, BR8EQ14 in trailing
And couple photos. They show some stuff that's no longer there but the ignition system has remained unchanged (aside from new cables as compared to the second photo).
The main issue (or really the issue) I'm running into is that my leading ignition randomly doesn't fire. This is observed via an inductive timing light as occasionally missed light pulses. What's odd though is that if I disconnect one module and run the remaining one through the cap, suddenly there's no more missed light pulses and the car runs a little bit better (far fewer misfires resulting in a pop out the tailpipe). This is true of both ignition modules/coils when running in 'non-DFI mode'. I've also tried different wires when running DFI and it doesn't change a thing. I thought perhaps it was the plugs, but they're brand new and should work fine. Plus, why would a less powerful ignition source (as in through the cap) be capable of firing a plug while a more powerful source (aka DFI) can't reliably?
In terms of possible causes I've only come up with a couple ideas so far. First, perhaps both modules running at the same time is drawing too much power, although that seems highly unlikely. The second is that perhaps with both modules running the pickup signal isn't sufficient or is being interfered with. I don't have access to a scope unfortunately, so testing that would be rather difficult. I'm wondering if smaller pickup wires might be in order, although moving them around the engine-bay/next to or away from noise sources doesn't seem to affect the issue.
One thing I did try with some success was a different dizzy, however it did not improve the random misfire situation when comparing between through the cap and DFI. Reason for the switch is that my other dizzy has very loose pickups. I'd known about it for a while but never got around to testing the effects. Apparently it's part of the equation, but not the whole picture.
So then, does anyone have any ideas? I'm a bit stuck on where to go next. Could the ignitors be awry? The front rotor setup does seem to misfire more often than the rear. Any clue why running through the cap seems to hide the issue?
The spark plug wires are rated at 350 ohms per foot so they're within spec. I did not check the trailing wires as currently they appear to be working fine, and I have tested them in the recent past and found them to be in spec.
I forgot to mention the coils I'm using which are MSD Blaster 2 High Vibration coils. They have a primary spec of 0.7 and a secondary spec of 4.5k. Since coils are typically checked when warm - which was not the case when I tested them just now - to me the higher secondary resistance seems logical. I've tested them before warm and they've been within spec, although tomorrow I could test them again while warm if that seems warranted.
The ground resistance between the ignitors and the battery is 0.4 ohms.
That should cover most of it. Tomorrow I'll also measure the resistance of the gutted ignitor, but otherwise it looks like everything is within reasonable limits (aside from perhaps the ground, although I would call that tolerable).
Measure pickup coil resistance and compare leading/trailing. Put eyes on wiring from sensor to connector. Ohm test while manipulating pickup wires. Eyeball sensor airgap,better yet measure with brass feeler gauges.
What is voltage at + primary of of ig coil(s) terminal with car running?
In terms of observations there is no visual damage to any pickup wires, and no values changed if measuring while manipulating wires (this is also true of the pickup 'jumper' wires that run from the dizzy to the ignitors). Unfortunately I do not have brass feeler gauges so the values displayed above were derived from me eyeballing the gap compared to a set of calipers. It should also be noted that the pickup coil resistance of the installed dizzy was measured after it had been sitting in the sun, while the spare dizzy had been sitting in the shade in the garage. Both are now in the shade so I can check them again later once their temperatures equalize. The gutted ignitor also checks out with a resistance of 0.0 - 0.1 ohms. Lastly the car does run ever so slightly better with the spare "dirty" dizzy, although it's now disassembled to be ready for swapping the pickups over to the "clean" dizzy.
"So if you mix and match your modules, you’ll have them trying to provide different voltages to the distributor pickup, turning on at different times and turning off at different times. This likely ends up causing both modules to misbehave badly."
The easiest way to check if your modules are the same is to disconnect the wires from W and G and measure the voltage @ W compared to ground with the ignition on (12V to the module) and engine not running. The 3 modules types that I'm aware of should have .77V, 1.25V or 0.00V. If both have the same bias voltage, the modules should be able to be used together.
My setup is almost identical, with the exception of using Ford TFI coils and OEM HEI modules.
I also had an issue with missed sparks on my leading system. Switching my signal wire to shielded wire and running it away from all other wires resolved my problem.
Toruki, I'm fairly certain they are the same part/part number - I bought both brand new at the same time, same packaging. I've noticed that those numbers are different as well, although I always figured it was just a batch code.
Joekaistoe, cool, I'll check that next chance I get (currently raining here in the wonderful Pacific Northwest). I've thought about trying some other coils, although right now that's not a cost I can justify if my current ones are working fine. I believe folks have said the TFI coils or similar FC coils do work a little better than the can style. Curious where you got your OEM modules.
Yeah, I'm sort of wondering if that's not still it; an interference issue that is. With the DFI setup I've got two "higher" powered high tension leads running right by the pickup wires. While I haven't noticed a difference with moving them around/away from the plug wires, when running through the cap they are exposed to lower levels of EMI since one, it's only one coil, and two, they wires are further away and firing half as often. Just to reiterate, I don't see any missed sparks when running leading through the cap like stock. I can also attest to the fact that there is a good deal of EMI present because if I try to use an infrared thermometer in the sparkplug area with the engine running it gets all screwy. How did you go about shielding the wires, and what routing did you take? How long is the run? What gauge wire?
Thanks all for the help thus far.
Last edited by Benjamin4456; 05-25-20 at 01:17 PM.
How did you go about shielding the wires, and what routing did you take? How long is the run? What gauge wire?
I used foil shielded audio signal wire, using the J109 screw as the shield point and leaving the shield unterminated at the far end, routing right next to the trailing high tension output (I just now really thought about lol), about 18" of length.
Install looks good Toruki, and thanks for the info. I particularly like the sheathing on your pickup wire cable - I'm just using some el cheapo corrugated stuff. My wire run is a hair over 2ft, although it doesn't get quite as close to a spark plug cable as your setup does.
I got a chance to measure the modules and discovered something a little interesting. On both modules the W pin reads ~1.336V which doesn't quite match any of the one's listed; strange. What I find more intriguing, though, is that my G pin's show ~1.350V - are they supposed to have a bias voltage? Both were tested in reference to the battery ground with the pickup wires disconnected.
FWIW worth mine seems to run just fine all the way to red line, and both of my modules measure 1.3 V. Per JoeKaistoe's info it's more important that the HEI modules match rather than exactly meet the values in the category. For the pickup wire, I think the shielding doesn't hurt of course but folks have commented here many times that they didn't use it and their direct fire systems worked fine. I have only this one example where others have much deeper experience.
One thing folks have cautioned is to make sure you have the pickup polarity correct on the W/G pins, you can reverse it as a test and it would be noticeably better one way or the other. I recall that tg_farrell had investigated the shapes of different distributor reluctors and found that some years worked better than others, 83 being the best (??!!). And *I think* he had to reverse polarity intentionally on one year's style to get the good performance.
FWIW worth mine seems to run just fine all the way to red line, and both of my modules measure 1.3 V. Per JoeKaistoe's info it's more important that the HEI modules match rather than exactly meet the values in the category. For the pickup wire, I think the shielding doesn't hurt of course but folks have commented here many times that they didn't use it and their direct fire systems worked fine. I have only this one example where others have much deeper experience.
One thing folks have cautioned is to make sure you have the pickup polarity correct on the W/G pins, you can reverse it as a test and it would be noticeably better one way or the other. I recall that tg_farrell had investigated the shapes of different distributor reluctors and found that some years worked better than others, 83 being the best (??!!). And *I think* he had to reverse polarity intentionally on one year's style to get the good performance.
Kind of, what I found was that to even get an 80 dizzy to work reasonably well it had to have the reverse polarity on the pickups compared to an 81-85 dizzy. I then used an 83 dizzy I had acquired and unreveresed the polarity and it worked like a champ. Looking at the signal wheels on the 2 dizzies shows you why this is the case. Also, shielding is a must, even if its just tin foil wrapped. Just make sure its only grounded on one end. I like that audio wire you used Toruki, may get some of that when I redo my DFIS (again). Always tinkering with it.
Huh, ok. My engine runs to redline quite well too, but it's at idle and low rpm that I can both hear the misfires and see them on the timing light. The polarity is also correct, as I've tested it before in the past, and when it's flipped the timing is far retarded and the engine runs considerably worse. And yeah, the 1980 dizzy has a reluctor wheel with the opposite profile as the 81-85 models - that's why flipping the polarity is required as t_g _farrell touched on. If I recall correctly though, the FB dizzy is still superior even when compared to a 1980 dizzy with the polarity flipped.
You know what, I might just have to try some tin-foil. I mean, it can't hurt to try it so I might as well. There's actually a chance that I have some shielded audio wire laying around (or at least I know I have some assorted good quality audio wire, perhaps not shielded). If I find that I'll give it a shot as well.
Install looks good Toruki, and thanks for the info. I particularly like the sheathing on your pickup wire cable - I'm just using some el cheapo corrugated stuff. My wire run is a hair over 2ft, although it doesn't get quite as close to a spark plug cable as your setup does.
I got a chance to measure the modules and discovered something a little interesting. On both modules the W pin reads ~1.336V which doesn't quite match any of the one's listed; strange. What I find more intriguing, though, is that my G pin's show ~1.350V - are they supposed to have a bias voltage? Both were tested in reference to the battery ground with the pickup wires disconnected.
Here's the exact voltages for documentation sake:
Rotor 1
- W: 1.335V
- G: 1.348V
Rotor 2
- W: 1.337V
- G: 1.352V
I believe the initial bias voltage can vary a bit depending on what voltage it's receiving at the positive terminal
G is coupled to W by a 10kOhm resistor, so it will mimic it's voltage when not receiving a signal.
Credit where it's due, Lou Dudzik put all this information together on his site in his work adapting the HEI modules to work on a couple different motorcycle ignitions. That link is to his specific information about the aftermarket modules with ~1.25V bias voltage.
My shielded wire is some 16AWG stuff an electrical engineer friend of mine got me, I think it's designed specifically as instrumentation wiring. I connected the ground on the ignition module side. Signal wire connection DLIDFIS Setup Signal Wire Info 1 Signal Wire Info 2
Please forgive the abhorrent mess that is my engine bay wiring.
Last edited by Joekaistoe; 05-26-20 at 10:34 AM.
Reason: Clarity
My shielded wire is some 16AWG stuff an electrical engineer friend of mine got me, I think it's designed specifically as instrumentation wiring. I connected the ground on the ignition module side.
Please forgive the abhorrent mess that is my engine bay wiring.
That stuff looks good, If I'd had that I would have used it instead of the audio cable which was fiddly to work with...
Originally Posted by t_g_farrell
Kind of, what I found was that to even get an 80 dizzy to work reasonably well it had to have the reverse polarity on the pickups compared to an 81-85 dizzy. I then used an 83 dizzy I had acquired and unreveresed the polarity and it worked like a champ. Looking at the signal wheels on the 2 dizzies shows you why this is the case. Also, shielding is a must, even if its just tin foil wrapped. Just make sure its only grounded on one end. I like that audio wire you used Toruki, may get some of that when I redo my DFIS (again). Always tinkering with it.
Thanks, Tim, for providing accurate information from my vague recollections!
What I used is labeled "Phoenix Gold Compact SUPER Triple Shielded Series" and I had it lying around from old car stereo installations waaaay back in the day. I wouldn't recommend using this specific stuff because it was such a pain to work with. I think JoeKaistoe's stuff looks better for this purpose. I ended up combining part 1. shields from the red and white sides. For the actual signals, I combined 2+3 red to use for pickup pin 1 and 2+3 white for pickup pin 2.
A good deal of progress has been made and the misfire is now far less prevalent than before.
It would appear that the misfire is/was related to the pickup coil signal. I rebuilt my dizzy with some pickups from a spare and set the air gap to 0.032" (that gap was suggested in another thread as good place to aim for an optimal signal). With the 'new' dizzy the misfire disappeared almost entirely, although it does still occur on cold starts (albeit to a lesser degree) and very occasionally when warm. Both pickup coil sets tested good, so perhaps it was the better gap that helped things. One additional thing to note is that the new pickup's have far less play, so that may also be a contributing factor. Anyhow, the car cruises extremely smoothly now and idles quite well so I'm happy. Should be a lot easier to tune the carb now too, seeing as how I won't be chasing my tail trying to tune out an ignition misfire.
Next thing to try is some shielding.
For now I've got one question for y'all. Do you folks still have the condenser hooked up when you go DLIDFIS? I still have mine present and connected, although for the first day of testing with the new dizzy I had forgotten to plug it in, and if anything the car ran slightly (read negligibly) better. Just curious. For what I know it's supposed to alleviate some noise in the electrical system, such as that that could be observed through the stereo, although I didn't notice much of a difference.
.032 airgap was found to give best signal/voltage from low rpm,@.4-.5 ac volts at idle speed with lots of experimentation,lol. It is a finicky low power sine wave that's susceptible to corruption in long wire runs and less than ideal connections. .4-.5 volts is best case scenario and low rpm voltage generated often measured only .2-.3 volts. This lower voltage has a less defined signal(weaker sine) and some ignition modules don't trigger reliably on it. OP may have been experiencing this issue,think i touched on this issue in prior thread.
I see no reason to delete oe noise filter. OP,if you think your car ran perceptibly better with noise filter disconnected,perhaps look at ignition coil voltage car running with/without filter connected. Perhaps it is beginning tofail and pulling primary ignition voltage down.
05-23-20, 08:00 PM
