PCM Electronic Wizards and DTC Codes

So the car crapped out at Houston and then wouldn't run at TWS. Thanks to the LT1 Gurus who shared some brain power.

I changed the coil and ICM at the track; no bueno.

Bought a cable from AKM, downloaded Freescan and peered deep into the bowels of a stock '94 PCM.

The codes for the missing automatic trans stuff made sense. The code for the low coolant temp made sense since I unplugged it at TWS. The other codes (26,27,29) seem to be emissions related.

PCM has the idle set to 600 which is where it idles. I started it several times, cleared the codes, and the emissions codes came back ~ no surprise.

No opti related or other ignition related codes. No PCM fault related codes. Even at 205 degree water it would rev to the limit where it had stumbled and bogged at the track.

Any other ideas?

Check all your grounds.
Block to chassis grounds.
Engine harness grounds.
Battery to chassis ground.

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Originally Posted by Fbody383

So the car crapped out at Houston and then wouldn't run at TWS.

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So what did you do to the car between Eagle's Canyon and Houston?
Retrace your steps ...

If you haven't already... search around on Camaroz28.com forums. There are still a couple of really knowledgable guys on that site and years and years of threads to search through.

Especially pay attention to threads that Injuneer post in.... he really knows these engines.

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Originally Posted by mitchntx

So what did you do to the car between Eagle's Canyon and Houston?
Retrace your steps ...

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Put it on the trailer, took it off the trailer. I might have even looked at it twice.

Been doing some digging and I'm starting to think it may be knock sensor pulling the timing. The exhaust leak at Houston could have contributed to some of that and apparently the LT1 sensor doesn't like roller rocker noise. I have some noise from the belt tensioner or A/C idler that could be confused for knock/ping.

Shoebox has some insight on testing the knock sensor wire ~ +5V from the PCM that gets grounded by the sensor so that's the next check.

*** Is it class legal to run an LT4 knock sensor module in the PCM? ***

Early indication is that they are less sensitive to valvetrain noise than the original LT1 units.

Tell me again what it's been doing....I remember you cracked an exhaust manifold at Houston, replaced it afterwards and it didn't run "right" at TWS but I don't recall specifically what it was doing. No power under load and wouldn't go over a certain rpm but free-rev'd just fine?

Some random thoughts:
1. Not sure if the code 26 is an issue or not. I seem to remember something about the evap circuit being something to keep even on a racecar but I might have that wrong.
2. Knock retard will reduce power somewhat but usually not to the extent you're describing. The LT4 knock module never made one bit of difference on my car when I was dealing with knock. I personally think it's an internet myth.
3. Download TTS Datamaster (there's a free trial version good for 30 logs) and log it with the engine running. Let it warm up and go into closed loop mode (you can see that in Datamaster). Look at the O2 sensor outputs, fuel trims, coolant temp, timing, spark retard under load, etc. Send me the log file and I'll see if I can help figure it out. [email protected]
4. Maybe you cracked a plug replacing the exhaust manifold? If not that, maybe one or two loosened up on you? Happened to me once...
5. Put an ohm meter on the coil wire...I've seen weird things there before.
6. The rotor inside the opti could be cracked or loose...it'd run like crap but not throw any codes.
7. Like Glenn said, check all your grounds.

Keep posting up what you find...it's bound to spur some other ideas I just can't think of right now.

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Originally Posted by Fbody383

*** Is it class legal to run an LT4 knock sensor module in the PCM? ***

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That is a big negative Ghost Rider.

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Originally Posted by mitchntx

So what did you do to the car between Eagle's Canyon and Houston?
Retrace your steps ...

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I had to rethink...

Nothing between ECR and Houston.

Car was down at dyno day but so where a couple of others. Car ran ok first race at Houston and finished 5th. Second race it started making the whirring sound that ended up being a combo of blown out exhaust gasket and EGR port on the passenger side manifold. I R&Rd the manifold gasket and replaced the plate with an EGR tube laying around. I don't think the power has been off the ECM either.

I'm downloading Datamaster and will try that tonight. Also going to pull the connector to the knock sensor and follow the Shoebox tips. The only thing that jumps out with Freescan is the knock count. I'll check for intake/exhaust leaks too.

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Originally Posted by Glenn_The_Hun

LT4 knock module? You'll do no such thing!!!

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That's why I asked. :cool:

Appreciate all the help guys; gotta make a better showing at Hallett than last year.

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Originally Posted by Fbody383

I had to rethink...

Second race it started making the whirring sound that ended up being a combo of blown out exhaust gasket and EGR port on the passenger side manifold. I R&Rd the manifold gasket and replaced the plate with an EGR tube laying around. I don't think the power has been off the ECM either.

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You mean the EGR port on the back side of the passenger exhaust manifold, near where all those grounds attach to the head? ;)

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Originally Posted by mitchntx

You mean the EGR port on the back side of the passenger exhaust manifold, near where all those grounds attach to the head? ;)

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I'll check again the next time I'm over there, but I don't think i have any back there.

I DL'ed the DataMaster software (it's pretty cool) and am getting ready to drop a couple files to Casey.

I had another thought this evening ~ could the catalytic converter be plugging up when it gets hot? I know, I know... "why is that thing still even in there?" Just 'cause.

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Originally Posted by Fbody383

I'll check again the next time I'm over there, but I don't think i have any back there.

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You should have 2 or 3. Those are the grounds for the PCM.

Your cats are clogged. Get rid of them.
Mitch has cats, not you.

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Originally Posted by mitchntx

You should have 2 or 3. Those are the grounds for the PCM.

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This is what I have: http://shbox.com/1/harness.htm there is a PCM ground by the starter, and it's just one wire, and then two grounds on the rad core support.

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Originally Posted by TheEnglishWizard

Mitch has cats, not you

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I'll pull it and give it a look. Don't want it to be too loud though... it might start sounding like a race car.

hmmm ... David, yours is an OBD1 car, correct?

Mine is an OBD2 car. Might be a difference.

But I seem to recall Glenn's 93 having ring grounds on the back of his passenger side head.

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Originally Posted by mitchntx

But I seem to recall Glenn's 93 having ring grounds on the back of his passenger side head.

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You could well be right.

My current understanding is the 93's are speed density and a beast of their own, the 94-95 (mine is 94) are more like OBD1.5 with the 96 on being true OBD2. So I have a 12 pin OBD1 port but I need a scanner (tool or software) to pull/reset codes and stream data.

I'm gonna try to pull the catalytic converter soon and give it a closer look.

This is a good exercise in learning more about the car though.

Painless harness. They can pick their own ground locations.

So back to the symptoms...it starts and idles cold, revs fine cold. Once it warms up it hesitates like mad when trying to rev it and if left to idle it stumbles to the point of stalling. Have you put it under load when cold or only once warmed up?

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Originally Posted by Al Fernandez

So back to the symptoms...it starts and idles cold, revs fine cold. Once it warms up it hesitates like mad when trying to rev it and if left to idle it stumbles to the point of stalling. Have you put it under load when cold or only once warmed up?

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It only really stalled and stumbled horribly at idle once or twice at TWS after a couple full throttle passes up/down the entrance road.

At Houston it made about 3 laps from cold for Race 2 when the problem first started. Started making that "whirin' sound" which was a combo EGR block-off leak and blownout exhaust gasket on 8.

When I was doing the PCM scans in the garage, it seemed like the passenger floorboards got hotter than I rememberd. Next step is still to pull the cat and put in a muffler. Since the scans look really pretty decent (a little rich down low off throttle, only DTC codes for missing automatic trans and emissions), Casey jump in if you disagree, I'm thinking it's a backpressure issue due to the cat failing.

(NOTE: I called the local muffler place and was told the owner won't let them cut out cats even on off road vehicles. So I called my State Rep to complain about increasing government intrusion. And why in the hell does the fair state of Texas need to collect 6.25% sales tax on every used vehicle sale? BS, I say.)

What say you, Mr. Cake?

ps - I'm registered to do most of a day at Grandsport Speedway, CCW if that matters, on Sunday, 5/22. Gotta make sure I have something to drive at Hallett.

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Originally Posted by Fbody383

(NOTE: I called the local muffler place and was told the owner won't let them cut out cats even on off road vehicles. So I called my State Rep to complain about increasing government intrusion. And why in the hell does the fair state of Texas need to collect 6.25% sales tax on every used vehicle sale? BS, I say.)

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I had the same issue trying to get a muffler installed. I had to goto a few places. First time around ended up at a "speed shop" (that did not end well)because the regular shops said I'd need to get a waiver from the state. This last time I had better luck, two places said they'd work on it. Settled on a one off place, not a chain.

"(NOTE: I called the local muffler place and was told the owner won't let them cut out cats even on off road vehicles. So I called my State Rep to complain about increasing government intrusion. And why in the hell does the fair state of Texas need to collect 6.25% sales tax on every used vehicle sale? BS, I say.)"


Sawzall baby! Handiest tool in the shop and very therapeutic as well.

Not sure if you want to bring it to me in Luling but I can do your "custom" cat jumper pipe next week. I should have my lift installed this weekend.

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Originally Posted by Hood

Not sure if you want to bring it to me in Luling but I can do your "custom" cat jumper pipe next week. I should have my lift installed this weekend.

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I'm probably gonna break out the sawzall this weekend, get an appropriately sized muffler, and weld it up. I'll probably add a new driver side panhard bar mount and reinforce the upper panhard support bar while i'm at it.:cool:

Yeah, your logs looked perfectly fine. All the sensors are doing their job and reading normally, indicating a "mechanical" i.e. non-computer related issue. The fact that it ran good cold and then started screwing up made me automatically think something was changing when the PCM went into closed loop mode but I couldn't find a smoking gun in the logs at all. Bad cats could do the same thing though as they warmed up and made the clog worse. I think that's a pretty logical next step and a "safety" upgrade regardless in case you find yourself parked on some dry grass against your will ;)

Tomball Muffler & Brake - $100.
major tool used - Sawzall & welder
At the least, remove the cats, and knock the membrane out of them, and remount the hollowed out cats. See if it runs.

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Originally Posted by rleng1

Tomball Muffler & Brake - $100.
major tool used - Sawzall & welder
At the least, remove the cats, and knock the membrane out of them, and remount the hollowed out cats. See if it runs.

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Oh it will "run," in the sense that will move the car. I figure if I'm going to the trouble to get the exhaust out and cat cut out, I might as well put a muffler in. Then I'll sound cool like all the other mid-pack slackers.

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Originally Posted by casey_ss

I think that's a pretty logical next step and a "safety" upgrade regardless in case you find yourself parked on some dry grass against your will.

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I'm pretty good about getting into the grass on my own.

Dude, I up'd your off in turn 1 at TWS on Sunday. Look at #84 Sprint's last vid at about 12 mins.
I go off big and deep right in front of Mitch. I got to a point where I had to make a decision to go around the building or in front of the building.
Either my cool shirt leaked or I messed myself.

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Originally Posted by rleng1

Dude, I up'd your off in turn 1 at TWS on Sunday. Look at #84 Sprint's last vid at about 12 mins.
I go off big and deep right in front of Mitch. I got to a point where I had to make a decision to go around the building or in front of the building.
Either my cool shirt leaked or I messed myself.

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I thought ... wow, you go Randy.

He was driving it in DEEEEEEP.

Then ... where'd he go?

The inner Randy

BACKPRESSURE

So I drop the exhaust; I needed to check on the cat and it would give me a chance to pretty up the turndown I welded on a couple years ago.

I picked up the Y-pipe and cat assembly and it sounded like a case of spray paint. I didn't think they were supposed to do that. I'm taking her down to Grandsport Speedway next Sunday for a little caress/test -n- tune.

*** FOR SALE: One catalytic convertor refill kit ***

Since the beginning of time, men have often ascribed certain female traits to their cars; usually dealing with beauty and temperment.

This B$tch is pissed.

It may be the first time in a long time the motor has not had excessive back pressure. I may be joining the Proctor Fire club at Hallett since I know from the scans it goes rich off throttle.

Good news for you guys is the new motor will get to wait until next year.

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Originally Posted by Fbody383

I know from the scans it goes rich off throttle.

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Which is why your cat has no more lives... unburned fuel completes combustion in the exhaust and is a death sentence to the catalyst.

At any rate, you may blow your dyno numbers with this fix.

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Originally Posted by Hood

Which is why your cat has no more lives... unburned fuel completes combustion in the exhaust and is a death sentence to the catalyst.

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I'm sure banging it on the ground doesn't help it either

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Originally Posted by Hood

At any rate, you may blow your dyno numbers with this fix.

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I've thought about that a little; it was never a screamer even when the cat was "ok." Might have to put that cool suit cooler in now. Besides, I can always throw in a restrictor.

when i removed my cats, saw an increase of about 10hp. went from 249 to 259 hp.

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Originally Posted by rleng1

when i removed my cats, saw an increase of about 10hp. went from 249 to 259 hp.

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But that is the mighty-mighty LS1. Maybe now I can get to 250...

Good News... Hopefully that fixes the problem.

I hope to fire mine before the weekend is over with the different engine.

I would really like to see you re-dyno prior to Hallett. Your call.
The CAT could have been clogged from day one, thus the reason it was never a screamer.

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Originally Posted by GlennCMC70

I would really like to see you re-dyno prior to Hallett. Your call.
The CAT could have been clogged from day one, thus the reason it was never a screamer.

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It is certainly possible; it did pick up with the new valve springs for 2010 but has been running somewhat warmer at the last couple of events.

If I can squeeze in an official dyno, I'm open to it especially if it seems pretty snappy after I drive it this weekend. Plan B might be to put the "black box" on it Friday at Hallett and Plan C would be put in an SWAGed sized plate.

I'm aware of the risks.

Good deal.

Very good news man. I'm a little surprised about your choice of welding projects (yes to cage, no to exhaust) but to each their own ;) Glad you'll be making Hallett!

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Originally Posted by Al Fernandez

Very good news man. I'm a little surprised about your choice of welding projects (yes to cage, no to exhaust) but to each their own ;)

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Falls into the mandatory vs. optional category. And with the time it took to troubleshoot, I may have run out of days to get a muffler in it. We'll see how it runs/sounds Sunday after some laps at Grandsport.

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Originally Posted by Al Fernandez

Glad you'll be making Hallett!

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There are races and then there are RACES; given my experience to date, I might have to bring "spares."

Ok, so I have a couple of new rules to live by in my racing life:

1) The Mitch Rule: Cats, furry or otherwise, have no place in or near a race car.

2) The Gas Rule: For some explainable reason, probably already covered by Dr. Pederson in the forum, race cars stop running when they run out of fuel... regardless of the position of the needle in the fuel gauge.

3) The Infinite Rate Spring Rule: Again, Dr. Pederson has probably already discussed the change in spring rate when one attempts to compress a spring laying on it's side. So now I know, a rear pigtail spring in a 4th gen can fall over sideways without falling out of the car.

I also learned (again) that there should be a test given to drivers before they're allowed to purchase a German car with 400 or more horsepower; I didn't know that my little, cat free, 114k mile hot rod would outdrag an M5, oh well.

Looks good for Hallett.

Thanks again to Casey, the LAW, and everybody else that helped troubleshoot the car at TWS.