Timing jitter, or is it a misfire?
 

OK, I admit, I'm a detail fiend, and maybe getting over-obsessive about this damn smog check: I want to pass it first time no hassles, but I'm making myself crazy trying to ensure I will - - with no way to actually know til I go. But going and not passing costs money, here.

Build: Stock 80 12A with all Cal emissions in place (which differ from others mainly by inclusion of an EGR system, which has tested out OK). Exhaust is restored to stock with exception of an RB muffler, and all seems tight. Core has roughly 3000 miles on a very complete &careful rebuild, and carb as well is freshly done over.

I think I've got the carb tuned to idle as best as I can per spec without an EGA to check CO, and I've worked most of the way thru the emissions components tests in the FSM without finding anything out of spec. The air control valve checks out fine.

Idle is right at 750 by my diagnostic tach, with a very small fluctuation of maybe 4 or 5 RPM; just enough to where you can see the needle move.

Here's the issue, though:

I'm seeing a pretty constant jitter on leading timing when at idle; I can see the mark bounce around noticeably, by about 1/8th inch or a little less. The idle seems a little unsmooth compared to what I remember, to where the engine visibly vibrates at idle.

Also, I think I hear a 'sneeze' now and again, which may be a misfire - - I notice this a lot while warming up, not nearly as prevalent once up to temp; makes for a non-constant, non-rythymic 'burble' in the exhaust note.

The trailing timing, ironically, seems rock-steady.

Questions are:

Should my timing/idle be more stable than what I'm seeing, or am I sweating a detail that isn't really there?

Am I now over-lean, or is this more likely an ignition issue?

What is the best way of detecting a for-sure intermittent ignition miss?

Are they subtle, or really noticeable? (Not had a misfire problem before, unsure how they behave)

Has anyone ever seen similar behavior, and what turned out to be the root cause - - or was it even actually a problem?

I have spare ignitors, even a spare ignition box (80's were the only year that used them), but no spare coils. I have cleaned and polished all related grounds, & verified ground quality.

Advice and such from people who've dealt with SA ignitions would be greatly valued! I'd like to get the car in for smog in the next day or two.

ive never dealt with an 80, but i have done 79 points, and the 81-85 stuff...

my 79 passed smog, all stock, points ignition everything. the KEY is heat, they are not kidding when they call it a THERMAL reactor. also the idle needs to be a tad rich, a misfire, seems like it goes right thru the system, and will spike the HC's....

so i drove it to the smog place, hard, he pretested it, and it passed with emissions being nearly zero. he turned it off, for about a minute, while the computer booted up to do the test, and it almost failed. heat is KEY.

idle mixture with the points kinda varies with how good the points are, when its 100% you can run it pretty lean, if its not up to speed it needs more fuel. it needs to be rich enough so that it does NOT lean misfire.

for the ignition issue, its a little weird that its only on the leading, have a look at the, wires cap and rotor (unless its all brand new...). id be tempted to swap the leading ignitor. i'm not sure what kind of plugs an 80 is supposed to have, mazdatrix is listing a br8et which is the 3 prong plug i think

if it was doing the timing wobble on BOTH lead and trail it might point to something like a bent distributor shaft. it also could be something weird like the pickup to trigger air gap or something.

i would think it'll still pass, the points cars do, and that ignition is crap

Thanks for the benefit of your experience; I will make sure we show up HOT, and I may run the MAS out another quarter turn - - I know the thermal reactors require a bit of fuel to actually work with, and will get too cold if they have nothing to "chew" on. That's why the ACV doesn't pump air past them in their cooling jacket until the revs get halfway fast.

The plugs are brand new BR8EQ-14's; went in right before I did my first relight a week ago. The rotor and cap are not 'new,' but are not very heavily worn, and I polished all the contact points clean.

The plug wires are... hmmm, not sure how much operating time they actually have. They're not ancient, though. 8mm Silicones.

I checked the pickup-reluctor gap, and it's within tolerance, but on the high side of the range. Is that tweakable at all, or am I best off not trying to fiddle it?

I replaced the pickup coil set less than 10,000 miles ago - - bought new from Mazda at a price so low I only fainted. (Still have the old set in spare.) Dizzy shaft was well within tolerance at that time.

I think I'll swap the lead ignitor out and clean the rest of the connections, see if that helps. I have a few in spare. Where's my Arctic Silver?

I'm also going to try using my old CRT o-scope to capture the lead trigger waveform; it's not an automotive scope, so I have to stick to the low-voltage side. Might be able to spot any missing triggers in the pulse train.

What's your take on the "Alcohol trick?" Helpful, or likely to throw things out of balance?

OK, I swapped out the entire control box (including both ignitors) to my spare, and cleaned all terminals, and I don't see any notable change.

I'm going to switch back to my other box, which is newer, once I clean the terminals & re-do the heat sink paste. The newer box has a matched pair of later-series-number J105's, so the newer-is-better rule applies.

Ohm-checked all the plug wires; all well within spec (under 1000 ohms each, in fact). Carefully seated each wire for maximum contact. No real change.

I increased idle speed by about 25 rpm, and gave the mix screw 1/4 turn CCW, which seemed to help smoothness a small amount. Exhaust doesn't smell too bad at this point.

I'm still seeing the jitter on the leading timing mark, though. The trailing mark (little harder to see, as it's red) still seems solid like a rock. I still hear, very subtly in the exhaust note, what sounds like a miss or sneeze, roughly a couple times a second. It's very hard to hear: Even with my ear close to the exhaust, you have to concentrate to hear it over the sound of the fan, engine, and fuel pump.

I guess swapping the coils would be next, but I frankly don't see how it could be a coil issue. I'm just running out of probable causes for my maybe-not-really-a-problem.

I'm going to try to get some video of the idle that will clearly show this stuff. Not the easiest things to video tape.

Then maybe you guys can tell me if I'm just chasing ghosts, or have a legit issue.

Wow... Original stock coils, I do believe...?

http://img.photobucket.com/albums/v2...f/OEMcoils.jpg

Yes ^

OK, I swapped the coils L-T and it made no difference (didn't expect it to, really)

So, at this point, I've test-swapped everything in the ignition except the plug leads (which tested fine), the plugs (brand new), and the dizzy coils (relatively new) and dizzy mechanicals (old but no noticeable wear).

Here is a 2 minute-video illustrating what I'm hearing/seeing (about 7 megs size):

http://img.photobucket.com/albums/v2...osis010109.jpg

Am I worrying about nothing, or could this be significant enough of an issue to cause me to fail smog?

If it's an issue, where can I start looking for causes?

Your opinions, please.

Hmm, seems like your engine sounds pretty good. I've been having some vibrations in my car too that is mostly audible so I got annoyed and took it to a local rotary specialist. He confirmed that my transmission mount was split in two so I replaced that and it did make the car feel more solid shifting through gears and helped the vibration a little but it still did not get rid of all the vibration noise.

What worries me the most now is that he told me he had a feeling the vibrations are coming from inside my engine like the counterweight, flywheel, or rotors so I need to check on that soon. But it seems like your water bottle wiggle test looks the same as my engine. I asked the mechanic if timing so off could cause that much motion but he said no. Something is out of balance. So I'll keep you posted also.

It sounds like its running pretty good. You say the leading timing with the light is not rock steady? If thats the case then thats the cause of the slight miss your experiencing.

The 80s are notorious for cross talk on the ignition harness that leads from the distributor to the ignition box that houses the igniters. Thats why in FBs they put the ignitors on the distributor.

That harness goes down from the dist. under the AC bracket and over to the driver side frame rail and then up to the igniters. Its a pain in the ass to get to all of it. You could try checking it out and see if its pinched or otherwise violated as it makes that journey.

Sounds like the rest of your ignition system components check out ok.

Sounds pretty much exactly like my 84 did stock, little puff puff puff when cold with the choke on, and the idle sounds about right. How did you set your timing? did you disconnect the vacuum advance and set it at like 2000rpm?

Thanks for the replies.

T G Farrell; I'll see if I can find any crimps in the pickup cable. You're right, it's a bear to get to without having to pull the AC bracket off.

The lead timing wanders a tiny bit, yes... about the width of the notch for the timing mark. A little less that 1/8" total. The trailing timing doesn't seem to do this.

Anyone know the conversion from distance on the surface of the pulley, to degrees timing? Or at least the accurate outside diameter of the pulley?

If the difference between the two marks represnts 20 degreees, then the fluctuation I'm seeing is far less than one degree.

I've tried to get video of the timing marks, but considering the brevity of the light flash from the gun and the framerate of the video camera, it doesn't come out looking anything like what I see actually looking at it. It's easy to forget that we're actually seeing an optical illusion when we look at timing marks.

You can see the fluctuation in the idle speed in the tach shot, though.

4portgsl: Thanks for the info. One of the hardest things about this is trying to remember what the car sounded like "normally;" I haven't had any others to compare to for many years.

I set the timing according to the instructions in the 80 FSM, which has it done at idle with all hoses connected. Is the 2Krpm-no advance method something specific to later years, or did I miss a trick along the way?

Main thing I need to know is, should the timing and idle be more stable?

Sounds like you guys are saying it should be, but not by much?

OK, I learned a little more, but I'm not sure what it means. Seriously need some expert help, here.

1) even at 2000 rpm fully warmed up, I can feel and hear the miss, but you have to listen close. Does this eliminate idle mixture adjustments from the equation?

2) I hooked my old dual-trace o-scope up to the 12v coil connections. It's not really suited for stuff as slow as an auto ignition. I can't see any missing lead pulses - - seems to be firing regularly.

3) It looks to me like I am getting some crosstalk, from the leading onto the trailing circuit, in the pickup coil cable... but I know this is not causing the misfire, because disconnecting the trigger side of the trailing coil entirely does not change the behavior of the miss. It stays exactly the same, if the trailing system is active or not.

I'm really running out of ideas here, guys. I need ideas to try, that don't cost piles of money just to test. I can't make myself think I have a chance of passing smog if I have a misfire.

What all can cause an intermittent misfire & slightly unstable idle (<>10rpm)?

1) mix too rich (carb is freshly rebuilt)
2) mix too lean (see above)
3) loose ground or connection (checked carefully, freshly cleaned)
4) bad high-voltage wire (ohmed out OK)
5) bad plug (brand new plugs)
6) worn dizzy shaft (per only spec I have, reluctor to pickup coil coil gap, it's OK)
7) Worn/faulty cap or rotor (look okay, and were polished carefully)
8) bad coil (test OK, and swapped lead/trail. made no difference)
9) bad ignitor or ignitor box (swapped to a completely different unit, no change)
10) bad pickup coil in dizzy (coils are pretty new, and seem to test OK)
11) bad pickup coil cable (haven't checked yet, but is new)

What else? What am I missing?

:wallbash:

my gsl-se does this too.. bothers teh heck out of me

Does it pass smog while doing it? Or are you in an exempt county?

go 83 dizzy, mines is an 83, and the 13b rx4 has a 12a electro dizzy in it, best thing i ever did. since your going newer year parts, it shouldnt be a problem.

also go get it pretested. most of the time if it passes they use the pretest papers and give you your smog right there:)

mine passed in the bay area... now i've got RB test pipe. so now it wouldn't pass.

Thanks, guys.

I happened to be in Long Beach today for work, and I stopped by at Mazdatrix; talked it over with one of the experienced service techs there.

Based on the discription I gave him, he also recommended that I just go ahead and get it tested; he said what I'd discribed is a pretty common thing with early 1st gens, and tends not to be an issue under load-testing on the treadmill. So long as my ACV and pump are working (and I've tested them per the FSM), he said, the TR should burn up anything emanating from a light miss while running under load.

So, I'm just gonna go and find out, either tomorrow night if I get home early enough, or Saturday otherwise. I even have a coupon for the local smog place.

Feel like I'm heading to a final exam.

If it doesn't pass, at least I'll have something in the way of new data to go on, too.

I bet it will pass, ill be rootin fer ya!

Not only passed...

Crushed it!

Code:

---

          15mph:      25mph:
CO2      12.70%      13.46%
O2        2.97%      2.79
HC (PPM)
    Max  214        181
    Ave    47        37
    Meas    7          6
CO (%)
    Max  1.36      1.16
    Ave  0.20      0.17
    Meas  0.00      0.02
NO (%)
    Max  1364      1224
    Ave    554        468
    Meas  303        174

---

Hot Diggity Damn!!

:bigthumb: :beer: :ylsuper: :peace:

Time to CELEBRATE. I'll have beer, the car'll have seafoam, please.

To all who have helped these last 7 months... many thanks.

woo hoo! i should take my car for its "midterm" lol.

Wow, thats really impressive. Makes me want to get another stock fb for a dd and keep it stock so it will actually pass emissions...

cleaner than mine was, good job!

btw if you're just idling it at 2000rpms, its going to hiccup a little, its like it needs the load to be smooth.

Also a trick you can do is to unhook or temporarily plug your smog pump so it’s not cooling your cats. .Then retard your IGN timing 5-10*. This will add a ton of heat to the exhaust. Drive it like a baby to the test. And once passed make sure to change settings back to normal. My car passed years ago by doing this.

so pretty much DD you wanted to guarantee that your car will pass smog and were concerned your little "jitter" would hinder your results. obviously your car was already in top notch shape to begin with since you nailed the cali test but i am unclear if you figured out your jitter vibration issue or were you chasing ghosts?