oldred95

On my 95 I've got this weird misfire I can't get rid of. I'm running the MAF code on TBI with the 16197427 pcm $OD mask. 61 pound injectors at 50 psi WOT with vacuum hooked to the regulator, 454 throttle body, 2 barrel single plane high rise victor junior intake, ported vortec heads and a LT4 hot cam. I've also got a Mallory digital 6AL ignition box and Mallory coil on it. I honestly don't remember when the problem started but I know it was sometime after I installed the ignition box because when I first put it on it pulled beautifully to 5500, now after 4000 it goes to crap. My pulse width is 3.9 - 4.0 at WOT when its doing it, AFR is showing to be around 14:1 but with the misfires I'm not sure how accurate that really is. It doesn't seem to be a lean pop either, just a dead miss. I've got a new MSD cap and rotor on it, new MSD super conductor wires and NGK platinum plugs. It was doing the WOT misfire thing long before the tune up so its nothing that I've recently added thats caused it. My MAF reading seems to be smooth and steady and I don't think its a spark advance problem. Any ideas on what it could be? The whole sync/async thing came up in coversation a while back and I noticed I had async disabled for some reason so I put it back to stock settings but enter at 3000 and exit at 2500 but it made no difference.

84elco231

Ignition problem was the first thing I thought of when I saw the post title.

oldred95

I added a considerable amount of fuel in the area its acting up and it did nothing but make my wide band show it being a little rich. I think I'm going to try my spare ignition module. The one thats in it was a new AC Delco module two years ago but that doesn't really mean anything.

whitelightnin92

i noticed with my injectors at high psi i couldnt run as much PW with them. may want to back the pressure down a hair. like 35 psi should be plenty.

oldred95

That could very well be but before I go opening up that can or worms I will swap out the modules with a known good one and see what I've got. Really I've been fighting this WOT misfire for quite a while now. Initially I thought it was due to painting the distributor cap as I was told that was a no no and makes the spark do weird things. Looking back I'm wondering if that paint didn't help trap some heat in and make the module weak and therefore messing with my WOT. Seems logical.

whitelightnin92

i had a module go bad a couple months ago and did the same thing. but the injectors will do something similar.

84elco231

Don't forget to use the correct heat sink compund on the mounting surface of the ignition module, it's a white paste made especially for the job. None of that silicone grease stuff, it won't transfer the heat out of the module.

Actually, I was thinking there might be a problem with the coil or even a bad plug wire, it's more difficult to fire a plug with a full (dense) charge in the cylinder and so the voltage will build higher and find any weak spots in the insulation.

oldred95

I'll have to see if I've got any of that. I think I probably used the silicone based diabetic grease last time. The plot may have thickened.

It did it before I put the ignition box and coil on too. The box and coil seemed to alleviate the problem for a while, it was still there just not as bad, but nothing has cured it. I have a hard time believing its a wire as they are new MSD's. The number 8 plug was gas fouled due to my old number 8 wire getting burnt on the headers and sending most of its spark to the header primary. I didn't change the plugs, I figured they would burn off at some point and they seem to have cleaned theirselves up but like you said under pressure it may not be firing right.

84elco231

You can obtain the heat sink compound from many electronics stores such as Radio Shack, nothing else will work to sink heat from the module. Many time a new module will come with a small tube of heat sink compound. Regualr silicon dielectric grease doesn't conduct heat from module, wasn't designed to.

Agreed, I doubt you've got a bad plug unless maybe it's carbon fouled or worn out. Wires are new and good quality, so you've got that one covered as well.

Probably module, coil, cap, or rotor??? Sounds like ignition problem to me.

oldred95

Well I swapped out the modules and right away it seemed to run different. It idled smoothly in park at 650 rpms at 14.2:1 for the first time in a long time. The air fuel ratio seemed much more stable and it didn't seem to have the flat spot around 2000-2500 like it used to. At WOT though it was still the same story. There ended up being enough excess of what looked like the original white grease on the original module to smear a thin layer all around it. I figured that would be better then the silicone based dielectric that was on the other module.

Still not sure what to think. I did datalog it but I haven't looked at it just yet. Its either fuel or lack there of, or spark. Maybe I should throw a set of plugs in it but its funny that it would only do it past 4000 rpms just over a bad set of plugs.

84elco231

Looks like you might have have to work backwards, check everything including base timing, etc. I don't run any kind of fancy plugs in older motors but I might go with a platinum if that's what the factory provided.

Could be a fueling problem as well, you'll find it eventually.

As an aside, I've got an olds 455 with thermoquad and straight-up HEI in one of my rigs but with those long stoke motors I don't like going past 5000 RPM anyway because the rings will pit the cylinder ends. This one tends to run out of oil past 5k anyway due to drainback issues as well, it might have too much oil pump. General rule of thumb is minimum 10psi for every 1000RPM and this thing's got way more than that.

oldred95

Went for a drive after work and datalogged it. As the rpms cross 4000 I noticed the pulse width began to level off it not drop slightly. At 3750 it was 4.68 with a MAP or about 94 kpa. After 4000 it began to make a little bit of vacuum, in the 92 then eventually 90 kpa range because of my restrictive air cleaner setup that I need to fix. But all the while the MAF reading kept rising which should have been adding fuel but apparently the stock 5.3 table just doesn't cut it on my engine. I believe the reason for the pulse width leveling off was because the engine was starting to make vacuum but at the same time for the given load it didn't have nearly enough fuel. At 3750 it was at 11.9:1 and after 4000 it was 13.6:1 and going leaner yet. I added a significant amount of fuel to it but I won't know until after work if it helped it or not.

whitelightnin92

soo... how is it now?

oldred95

Still breaks up only now its at 11.6:1 when its doing it. I've sent dimented a PM as I'm running the MAF code and he wrote it so maybe he can offer some insite.

InfernalVortex

iTrader: (4)

I had a misfire in that range in my car. Kept throwing parts at it and it actually got worse to where it was doing it above 3000 rpms instead of 4500 or so.

I could just rev it to 3500 in neutral and could hera it break up so it wasnt load dependent.

Turns out it was probably the magnetic pickup in the distributor.

I added new:

Distributor cap
Rotor
Coil
Module
dist gear shims
Radio Suppressor
Magnetic pickup

The last two I did at thes ame time and it fixed itself. I'm pretty sure the pickup was the problem the whole time. It also wasnt there when I first got the car together. It developed over the course of a year and got worse and worse. Sound familiar?

Good luck, hopefully you figure it out sooner.

oldred95

Thats encouraging and fairly cheap to try at that. Well maybe I will get spry here next week and drop an pick up coil in it. As far as I'm aware its the original 15 year old 202,000 mile pick up coil. If it is the coil I guess its done its deed.

84elco231

"[quote=InfernalVortex;4535480]I had a misfire in that range in my car. Kept throwing parts at it and it actually got worse to where it was doing it above 3000 rpms instead of 4500 or so.

I could just rev it to 3500 in neutral and could hera it break up so it wasnt load dependent."


I wonder if you could see any signs of breakup on your logger, or maybe your tach?

Thanks,

InfernalVortex

iTrader: (4)

I just noticed the symptoms and hoped I could help. I've actually got a carburetor on mine. If I was trying to narrow it down from ignition to EFI and back and forth I'd have probably pulled all my hair out over it. As it was I knew it had to be somewhere in the ignition. Hopefully it helps him find his problem, because no one even suggested replacing the magnetic pickup on my distributor when I asked around to figure out what the problem was. I've got an old school large cap HEI, but Im pretty sure the smaller ones have the same magnetic pickups in them, and I'd rather him trhrow a $20 part (at least for me it was $20) than a new module and coil at it. Modules and coils are expensive.

But the tach did jump around a lot. It would make 250-750 RPM jumps when it missed. It's a nice Autometer SportComp tach too, wired straight to the distributor, so I knew it was accurate.

84elco231

Exactly, I would expect if it were an ignition problem and it was coming from the primary (or low tension) side, it would show up on the tach or maybe data logger.

Something to take a look at....

If you're using vacuum advance, pickup coil conductors are something to keep in mind on the primary side. I'm mostly a carb guy as well, EFI can get a little dicey when it's been modified. I like to take it one step at a time in that situation.

Norwood

iTrader: (1)

just a few more bones for you to chase...an injector could be breaking down or restricted, fuel pressure?, and finally what about valve float? don't know the condition of your valve train but just something to think about.

whitelightnin92

mine is having similar issues as yours for over a year actually. i just put a carb on it to try and got it jetted right and still have the same issues. it doesnt neccesarily break up but it has no lowend, if i punch it, it lean pops. and it starts to run out of steam around 4500. this thing used to turn 6k and keep right on going. it has to be a ignition or valvetrain issue for me. im going to assume you would be having one of those issues as well. i replaced cap/rotor/plugs/wires/coil and even replaced the module with one off my friends camaro that was in known good condition. the only thing im unsure of is the autozone dizzy that i have in it

oldred95

Sounds just like mine. From a dead stop I've got crap for lowend. A LOT of it is due to the single plane sucking the intake dry when I stab it and fixes for that are in the works but for what this engine should be, it has never, ever, ever, ran like it ought to. It has had its moments but its never been quite right and never consistent.


As mentioned above, when its breaking up I can plainly see it on the tachometer. I have seen it somewhat in the datalog but it happens so fast its hard to play it back slow enough to be able to see it actually doing it but it is there.

I picked up a new Borg Warner pick up coil from Oreillys and they didn't have any thermal/heat sink grease so I went to Autozone against my will and although they couldn't find any either the kid was nice enough to give me a ration of it that comes in with the new modules. Now that they have gotten the rice out of Autozone the store actually seems to be half way decent. If things go good I will get the pick up coil put in sometime this week and maybe get the truck out and see what happens.

InfernalVortex

iTrader: (4)

Why does the vacuum advance matter? I dont use mine at all.

84elco231

The reason I mentioned vacuum advance is because every time the advance receives vacuum and moves, the coil conductors move along with it. Once these conductors have been flexed hundreds of thousands of times (or perhaps millions?), they tend to break down and get intermittent.

84elco231

The pickup coil conductors, that is...

95 4x4

iTrader: (1)

oldred95 i had something simular happen to me but not as sever . The reluctor had cracks in the magnets which was causing the magnetic fields to change . With the fields changing it was causing the pick up coil to react differently leading to misfires an very irratic running . Once i changed out the whole shaft , only way to replace reluctor the issues went away . Its just a thought .

Ronny

iTrader: (1)

In your .bin there may be a REV-RPM limiter as well as MPH limiter. Just a thought. I recall my motor breaking up when I hit the REV limiter(5800rpms). I have not hit the MPH limiter yet(200mph).

funstick2

unplug the tach lead from the ignition coil. I have seen a few cluster fialures cuase issues like this.

ownor

iTrader: (5)

had a similar issue as 95 4x4 described. however, it resulted in a no-start condition in my case because i cracked the bigger part of the reluctor while trying to get that (seemingly) 20 years old rotor off
anyways the only reasonable way to change that as already stated is imho to change out the whole shaft.

TKR Performance

iTrader: (1)

Anyone figure something out on this? My 85 Trans Am is doing the exact same thing... my tach goes all wacky over 4000 RPM's, and it misses and carries on. What's funny is not 40 minutes before this happened I took on a Skyline GT-R and it was perfectly fine. Parked it at the store, got back in it and now this. Any help would be appreciated!!

oldred95

I found the time at work last Friday to swap out the pick up coil. The distributor shaft had some crap buildup on it and I had to carefully drive the shaft out. I guess its a common thing but I didn't really appreciate it. Actually had to spray break away on it and work it back and forth a few times before I got brave enough to actually drive it out. Once that was done I found the pick up coil and it looked like hell. It was all ragged and nasty looking and the magnet(s) didn't look much better. I cleaned the magnets up and they didn't look too bad and in comparison to my spare distributor the magnets on my original distributor shaft seemed to be the stronger of the two. I took emery cloth and shined things up a little. I managed to find an old CPU heat sink at my parents house this weekend and I cut it up today and its going to be fastened onto the bottom of the distributor to help pull some heat out of the ignition module. If everything goes right I will drop it back in tomorrow and see what happens.

oldred95

The pickup coil did absolutely nothing to help the issue. Its as bad as ever now. It almost seems to be doing it a little under 4 grand now. I'm not sure what else to try besides matches. I guess I could bypass the Mallory box and see what difference that makes if any. Other then that what is left? Its getting plenty of fuel, almost 11:1 when its doing it, new ignition system other then the plugs which are NGK platinums, I've tried multiple sets of injectors, doesn't seem to be anything with the tuning, doesn't seem to be anything in the distributor.

TKR Performance

iTrader: (1)

Don't feel bad... I have a later model small cap distributor on mine, and when I pulled it apart the pickups were the nastiest rust color you could imagine. Then they broke in half while I was cleaning them (could that have been my problem????). So $100 and a new distributor later, my car runs worse than it did before. And yes... I marked everything and put the distributor back in the way the old one came out. I can't even see the 0 on my balancer, its up under the water pump and no matter which way I turn the distributor the car shuts off. So tomorrow I'm gonna take it to TDC, restab the distributor and hope for the best. Good luck on yours!

95 4x4

iTrader: (1)

Can you switch the module to a higher rev just to prove it out , incase the one your using now is bad . One other thing did you change your plug gap wider for the hotter spark ? If you did possible you went to wide i can see a .005 increase from stock , just throwing some stuff at ya .

oldred95

Are you referring to the rev limiter in the Mallory ignition box? IIRC I set it to 7000 rpms so that it would not effect anything and its not a bouncing rev limiter keep your hanging at one speed/rpm miss either, its a continues to accelerate slowly and continually misses kind of misfire. The kind that effects power but is not limiting engine speed.

I never messed with the plug gap. They came gapped at .060 inches. I've got another set of regular copper style plugs I can put back in it but its kind of a PITA because of the headers.

95 4x4

iTrader: (1)

Yes i was referring to the Rev limter . My truck is also a 95 an the stock gap is .035 the only time i increased the gap was when i added a high out coil an then i went to .040 . I don't no much about the Mallory set up you have but i think .060 gap is to much . Yep getting at the plugs is tough i cut a .625 plug socket length in half an use the wrench end .

oldred95

These are NGK G Power Platinum plugs and the gap was intended to be .060 with them and they were in there long before the misfire started happening. I have a Kobalt set of thru sockets or whatever they call them. Its still a PITA on numbers 5 and 6 any way you slice it but the Kobalts make it a lot easier.

I was sitting here recollecting, pondering, and analyzing thoughts and memories and things I've learned about what makes an engine do what it does. Its either spark or fuel causing this and I'm fairly positive its not spark at this point. I'm going to slap the fuel pressure gauge on it tomorrow at work so I can see it while I'm driving and go open it up on my lunch break and see what it does. I'm wondering if the fuel pressure isn't dropping under a load like the filter is restricted and rather then spraying fuel its just splashing it in there. I've driven it with a bad pump before and I had a similar miss, just at a much lower rpm. That being said when I first started noticing the problem it was happening closer to the 6000 rpm mark, maybe starting as low as 5500. This has been over a year ago and its slowly, steadily, gotten worse.

95 4x4

iTrader: (1)

I looked at your set up on Jeg's site an your coil only puts out 45,000 volts , which makes your plug gap to big .

95 4x4

iTrader: (1)

LOL must have been typing at the same time just read it . I agree the plugs are meant to run at .060 an i run AC platinums at .040 as the coil can only handle that much after that the spark is to weak at least in my case .

oldred95

I have a hard time believing its because of a lack of voltage.

JP86SS

iTrader: (1)

Fuel filter?

InfernalVortex

iTrader: (4)

Is there any way you can swap to a known working distributor? I already gave away my old one... if I still had it I'd send it your way to see if it helped.

oldred95

I think the problem is either the fuel filter or the TPS. It acts like it could be fuel but seeing as its showing rich if anything I kind of doubt it unless its just randomly splashing gas in because of low pressure which could fool the wide band. Was talking to a guy at work and his 94 did something very similar. Under or near WOT it would break up at higher rpms. I've noticed on mine if I back out of the throttle a little the problem lessens but its still there.

oldred95

Tried a TPS off my spare throttle body that was working when removed. Maybe it was just me but it seemed noticeably better. It did break up slightly as it crossed 4000 but it seemed to clear up for the most part although it was still low on power. I'm going to put a filter on it tomorrow and if that doesn't do it, I guess burn it.

whitelightnin92

i know with mine when i had big block injectors in it i couldnt get it to rev past 4000 without breaking up bad. i guess it was just trying to spray so much fuel i couldnt get it to do it very accurately. if i leaned it out it would read rich on the wideband, but be surging from a lean condition, and if i richened it up it would just break up from being overly rich.. i wondering if its your fuel pressure. its set pretty high and i cant imagine theyre very spraying very accurate at that pressure. i have better luck in the 24-30 psi range, but mine still has a problem aswell. i just did put the TBI back on since i now know its another issue because it did the same thing with my carb. it has to be the ignition system since i really doubt its the engine.


ooh yeah i meant to tell you. i was able to minimize the lean pop when going to WOT instantly by lowering the "maximum IAC opening during PE". it didnt totally eliminate the problem but it helped. i may eventually but the smallblock tbi back on for better throttle response. i dont see any need for the BBC TBI. it isnt any restriction, the intake manifold is the restriction.

TKR Performance

iTrader: (1)

Well I finally got mine fixed. I changed the distributor for a new unit. My advice is to put your motor at TDC before doing this. Each new dizzy seems like its geared differently. I stabbed the new one exactly where the other one came out and it was a few teeth off. Its amazing how much better it runs when all the spark is going where its supposed to lol. Good luck to ya'll!!

oldred95

Mine has been getting much worse. Its to the point it will hardly idle at all after a cold start. I thought it was a bad chip/burn making the PCM crash but it wasn't. I finally got it warmed up and cleared out and drove it and it breaks up really bad and now its starting a little before 4000.

I came back, made a different chip with a few little tweaks and put it in and started it to make sure the chip burnt ok and that it would run. It started and ran like crap, cleared up for a bit then would randomly almost die then surge and smooth out and repeat. I started smacking the PCM with my pen light and everytime I hit it the engine stumbled. I kept at it to make sure it wasn't a coincidence and I noticed the check engine light came on. I checked and the engine was still there but had set a code 17 which for my application is a Mass air flow signal lost code. I wiggled the wires to make sure it wasn't an issue at the connector and tugged on the MAF signal wire and it was all good. I think my PCM may be taking a dump on me. I've suspected it for years but its never really caused a consistent problem until now. Could very well be the cause of my misfire too. If I can get ahold of my buddy tomorrow I will try his spare PCM and see what happens.

A couple months back I kept getting a rough start, rough running and a code 17. The MAF sensor I was using at that time was questionable and replaced for a reason (I don't know what specifically) but looking back on it now I think it could have been the PCM acting up then as well. I replaced the MAF and although I'm not completely sold on the quality of the A1 Cardone I don't think it is the problem as of yet.

95 4x4

iTrader: (1)

Possible the chip and socket might have alittle oxidization on them or maybe the pins on the chip are bent alittle an losing contact ever so slightly .

oldred95

That could be but I pulled the board out of the PCM and found a couple of funny looking spots in the printed circuits near the memcal socket. I don't know that it's actually bad but it's got a funny look to it. I pulled the G1 adapter out and the zig socket from the G1 and it all looked clean. I will try it again tomorrow and see what it does.

whitelightnin92

im pretty sure mine is an electrical/ecm problem too. it just will not run right since the ecm swap. i would put the old ecm in but that would mean swapping in a 700r4