Misfire at Track

[PatrickB]

Could be a bad tach. We had a similar issue with a car in our group last season. Extremely difficult to pinpoint, and just for kicks, a tach was switched out, and IT was the issue!

[dgmark]

A shorted tach can be a problem, But way down the list. If it was my car this is how I would solve it

A Check Compression, Is the engine Mechanically Ok
B Check Fuel Pressure
C Put a Timing Light on the coil wire, run the engine, If you get a steady light that increases with RPM with no drop outs the primary ignition and crank sensor are most likely OK
D. put a node lite on the injectors one at a time, Is the lite blinking steadily?

Most likely with those 4 tests you will narrow down the problem to fuel, Ignition or mechanical. If you don't have the tools you should take it to a qualified mechanic anyway.

[Dublinoh]

Originally Posted by IROC

This happened to me once (or something similar - also 3.2 with Steve Wong chip). I pulled the plugs and found a couple of them with signs of melting. I had recently replaced my full throttle switch (had been running track events with it non-functional evidently), so I went to the local auto parts store, bought new plugs and installed them. I unplugged my full throttle switch and ran the rest of the event without any problems.

Long story short, what do your plugs look like?

The wrong (an inappropriate) heat range plug can also cause this.

[minoclan]

Originally Posted by Joe Bob

Well aren't you just a ball of piss of piss and vinegar? Who crapped on yer booster seat today?

WTF are you jumping into MY face for?

Great answer!

[Mattcamp]

Originally Posted by island911

Yes he is. ..and it's not just you he's looking to piss off. Loren is clearly pissed at the world.

Everyone here knows that Loren in a complete douche that is jealous of Steve Wong. Or is it douche bag? I forgot.

[JeremyD]

douche nozzle

and I had the same conditions - at the track - turned out to be a cracked distributor cap.

But then again, I tend to drive flat out, in the rain, at night...

[Steve W]

Originally Posted by kslizzy

At the track yesterday and my car started misfiring halfway through my second run session. Going into a hard braking corner, turned, eased back on the throttle and crazy misfire. Limped up the hill towards the pit entrance and it started running fine. I thought it was maybe fuel starvation even though I had an indicated half tank. The turn leading to the problem is a fast, uphill right hander into a tight left hairpin. I ran another lap and again after a hard braking zone the car misfired. Got it to the pits and it would not stay running without throttle input and even so it was very rough. I waited, thinking and hoping it was a vapor lock in the 90 degree heat. 2 hours later it still wouldn’t run. I trailered it home another 2 hours. It started to get it in the garage and it at least ran on its own but not well at all.

I replaced the fuel pump, fuel filter, cap, rotor, plugs two winters ago, maybe 2000 miles. Wires are probably 7-8 years old, 10-15k miles. I checked and had positive connection at cap and plugs.

Car is a 3.2 with Steve Wong chip, cat by-pass and M&K exhaust.

Any ideas?

Thanks!

I see issues like this quite frequently on cars when they come in to get dyno tuned. Although ideally when a car is brought in the car should be functioning 100%, half the time they are not, even fresh from the engine builder. The dyno tells everything, especially when the power is not coming in where it should or the, or the air fuel ratios are not coming in where they should statistically.

In no particular order, and not saying which is or isn't a possible cause on your car, this is what I see a lot. Some of these are very difficult to diagnose and take a lot of educated analysis and testing:

a) erratic part throttle misfiring and rpms cutting out at high rpms over 6000 rpm. Cause: 1 or 2 bad fuel injectors found as verifed by a IR temp reading off each header. I had 3 cars like this in the past 12 months.

b) high rpm cutout. Cause: due to overgapped flywheel sensor past 0.8mm, or aftermarket flywheel pin requiring a closer sensor gap to not cut out.

c) rpm misfiring and cutout at load and upper rpms. Cause: overzealous spark plug gapping causing the spark to not fire

d) random misfiring or cutouts. Cause: Failing/defective DME unit or DME relay causing intermittent spark or power

e) lean running condition and misfiring and cutouts at high rpms. Cause: Cars were an engine transplant with a non-Carrera tach converted by XYZ Speedometer that overdrove and blew out the IC in the Motronic DME - VERY COMMON!

f) same as above eventually blowing out the DME: Cause: Tapping into the upshift indicator wire from the DME for a tach signal for a aftermarket tach/upshift light/data logger etc, blowing out the DME

g) car running lean causing misfiring or maxing out the injector capacity: Cause: aftermarket fuel pressure regulator set below factory pressure

h) Twin plug motors or 3.6 engines not producing the power they should. Cause: one side of the twin ignition has failed. Failures include bad ignition modules, broken belts, and bad coils

i) 3.6 engine power lacking and peaking at 5500 rpm. Cause: faulty resonance valve operation

j) Dyno shows only 80% power and air fuel curve off. Cause: faulty WOT switch or car is not achieving full throttle, only opening 2/3'rd

k) air fuel ratios coming in at the rich end of the statistical range. Cause: faulty head temp sensor, including the newer two wire versions. Last one measured 1kohm hot, in the mega-ohms cold.

l) air/fuel ratios coming in at the lean end of the statistical range. Cause: air flow meter previously tampered with and internal clock spring tightened for whatever reason previous. Sometimes also done on grey market cars by the importer to lean out the mixture.

m) same as above but coming in very rich overall. The converse of the above where the air flow meter as tampered with and clock spring loosened, probably someone's attempt to 'tune' the car

These are just some of what I have seen and I don't remember them all and, but it happens so often it's frustrating for everyone as it drags out the day. But I can't always fault the owner or builder because a lot of this is hard to see or experience unless the engine is loaded such as on the dyno or being driven such as under racing conditions. Better on the dyno of course so the issue can be addressed rather than in on the road or track, but if you can't figure it out and don't find anything mechanically faulty, you might want to dyno it (preferably a Dynojet) and send the results to me to evaluate.

[Lorenfb]

"a) erratic part throttle misfiring and rpms cutting out at high rpms over 6000 rpm. Cause: 1 or 2 bad fuel injectors found as verifed by a IR temp reading off each header."

Then the 2 cylinder are dead and can't melt the spark plug.

"b) high rpm cutout. Cause: due to overgapped flywheel sensor past 0.8mm, or aftermarket flywheel pin requiring a closer sensor gap to not cut out."

Again, then no spark damage.

"c) rpm misfiring and cutout at load and upper rpms. Cause: overzealous spark plug gapping causing the spark to not fire"

Then just drop cylinder with not damage to plugs.

"d) random misfiring or cutouts. Cause: Failing/defective DME unit or DME relay causing intermittent spark or power"

Same as above.

"e) lean running condition and misfiring and cutouts at high rpms. Cause: Cars were an engine transplant with a non-Carrera tach converted by XYZ Speedometer that overdrove and blew out the IC in the Motronic DME - VERY COMMON!"

NOT TRUE! The tach output can be shorted to ground or +12 and no damage to
the DME ECM operation. The tach output is a buffered output. Just look at the schematic!

"i) 3.6 engine power lacking and peaking at 5500 rpm. Cause: faulty resonance valve operation"

Both engines are 911 3.2s. Guess again!

"Cause: faulty WOT switch or car is not achieving full throttle, only opening 2/3'rd"

Owner indicates that WOT mode caused the problem. Guess again!

"l) air/fuel ratios coming in at the lean end of the statistical range. Cause: air flow meter previously tampered with and internal clock spring tightened for whatever reason previous. Sometimes also done on grey market cars by the importer to lean out the mixture."

Owner indicates that WOT mode caused the problem, so the AFM inputs were
ignored, i.e. on the WOT map. Guess again!

"m) same as above but coming in very rich overall. The converse of the above where the air flow meter as tampered with and clock spring loosened, probably someone's attempt to 'tune' the car"

Again, owner indicates that WOT mode caused the problem, so the AFM inputs were
ignored, i.e. on the WOT map. Guess again!


Bottom line: Please, no more guessing!

[Canada Kev]

Loren, you're kind of an asshat, aren't you? You sound like one of those know it all engineer types that really doesn't, and has some major inferiority complex.

The OP didn't say that the WOT switch caused anything. SW is just listing things he has seen in his experience that may or may not apply, but could be checked. I haven't seen a lot of positive suggestions from you that might actually help the situation.

I would rarely speak up in a situation like this, but you know, douche doesn't even begin to describe. The OP has an issue and you aren't helping, so bugger off. Please. I for one, want to hear what's happening and learn something.

[Joe Bob]

Loren [Edited by a mod -- let's not get too personal, guys]....really shouldn't be so much a keyboard warrior.

[Steve W]

I'm not going to get into a pissing match with you.

Read the post again. It says, these are problems I see frequently, which may or may not apply to his car. These are problems I bring up for the the benefit of the community in diagnosing similar problems. It doesn't take a rocket scientist to know when I'm taking about twin plug failures on 3.6 engines, I'm not talking about a 3.2. If you have nothing constructive to contribute, then shut the hell up.

And FYI, failing injectors are not a run or no run condition - it's clear that's just an assumption that you pulled out of nowhere from lack of experience. They become inconsistent when they are either at the low or high end of their duty cycle.

Also, the AFM outputs are utilized in full throttle calculations of the air/fuel mixtures by the DME. Anyone that has spent any time on the dyno with a 3.2 would know that. But then you clearly never did, just "claimed" to. How to prove it? Loosen the spring tension by 4 clicks and dyno the car and look at the AFRs. Then tighten it 4 clicks the other way and repeat.

Bottom line, you don't really know as much as you think you do - go back to fixing your alternators!

[Lorenfb]

"The OP didn't say that the WOT switch caused anything. SW is just listing things he has seen in his experience that may or may not apply, but could be checked. I haven't seen a lot of positive suggestions from you that might actually help the situation."

Sounds like you did fully read what was said and obviously have no understanding of the
DME ECM and how it functions, affects the engine operation, and how it can damage
an engine. So maybe post your comment over in the OT about what the best polish.

Read again:

"I pulled the plugs and found a couple of them with signs of melting. I had recently replaced my full throttle switch (had been running track events with it non-functional evidently), so I went to the local auto parts store, bought new plugs and installed them. I unplugged my full throttle switch and ran the rest of the event without any problems."

[LJ851]

Loren, i am ashamed to share a similar name with you (Lorin) You truly have your head up your ass about the topics you choose to highlight here. I fully believe you are a competent individual but god damn, learn how to pick your fights.

[Lorenfb]

"If you have nothing constructive to contribute, then shut the hell up."

Such a lovely personality!

[Lorenfb]

"really shouldn't be so much a keyboard warrior."

- Joe Bob -

Please! Another one hidden behind a cryptic name like the many others who do personal attacks.
And who in actuality might you be, other than 23K posts of repeats of the previous posts in a thread.

[Steve W]

Originally Posted by Lorenfb

Such a lovely personality!

OUCH! hahaha!

[efhughes3]

It's my understanding that the OP is not the one with melted plugs-it was the second poster here citing that as something that happened to him.

[rick-l]

Anybody notice the original poster (post #1 not #2) has not replied?

And if it were me I would not put up with this crap. The only choice would be to figure it out myself no matter how long it took.

Originally Posted by kslizzy

At the track yesterday and my car started misfiring halfway through my second run session. Going into a hard braking corner, turned, eased back on the throttle and crazy misfire. Limped up the hill towards the pit entrance and it started running fine. I thought it was maybe fuel starvation even though I had an indicated half tank. The turn leading to the problem is a fast, uphill right hander into a tight left hairpin. I ran another lap and again after a hard braking zone the car misfired. Got it to the pits and it would not stay running without throttle input and even so it was very rough. I waited, thinking and hoping it was a vapor lock in the 90 degree heat. 2 hours later it still wouldn’t run. I trailered it home another 2 hours. It started to get it in the garage and it at least ran on its own but not well at all.

I replaced the fuel pump, fuel filter, cap, rotor, plugs two winters ago, maybe 2000 miles. Wires are probably 7-8 years old, 10-15k miles. I checked and had positive connection at cap and plugs.

Car is a 3.2 with Steve Wong chip, cat by-pass and M&K exhaust.

Any ideas?

Thanks!

[Canada Kev]

Originally Posted by Lorenfb

"The OP didn't say that the WOT switch caused anything. SW is just listing things he has seen in his experience that may or may not apply, but could be checked. I haven't seen a lot of positive suggestions from you that might actually help the situation."

Sounds like you did fully read what was said and obviously have no understanding of the
DME ECM and how it functions, affects the engine operation, and how it can damage
an engine. So maybe post your comment over in the OT about what the best polish.

Read again:

"I pulled the plugs and found a couple of them with signs of melting. I had recently replaced my full throttle switch (had been running track events with it non-functional evidently), so I went to the local auto parts store, bought new plugs and installed them. I unplugged my full throttle switch and ran the rest of the event without any problems."

Look dumbass, it was Mike that posted that and not the OP. Just like I said. Looks like I hit close to home with my assessment of your personality. It's interesting that one person can raise the ire of so many. Oh, that means make them angry...

So that this post is a bit cleaner than what I really want to say, I fart in your general direction. You're not worth the time to argue with.


Sorry kslizzy. It seems that your post has gone way off base and has turned into a slugfest. And I'm partially to blame. For that I apologize. I really do hope your problem gets solved without much further delay, and I would very much like to know what the root of the issue is. When this thread gets locked up, as it inevitably will, please post the solution in another. Good luck.

[IROC]

Originally Posted by Lorenfb

Read again:

"I pulled the plugs and found a couple of them with signs of melting. I had recently replaced my full throttle switch (had been running track events with it non-functional evidently), so I went to the local auto parts store, bought new plugs and installed them. I unplugged my full throttle switch and ran the rest of the event without any problems."

It appears you are the one who needs to "read again". The OP doesn't mention anything about melted plugs or the WOT switch - that's my issue. My engine needs some sorting top to bottom, so I have no idea what the real problem is, but do not have an issue with Steve's chip. For instance, as someone else mentioned, I was also using NGK "8" range plugs which are probably not correct.

You're so intent on attacking other people that you can't even keep the story straight. To imply that Steve Wong doesn't know what he's doing only reflects badly on you.