PCM Electronic Wizards and DTC Codes

[Fbody383]

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?

[GlennCMC70]

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

[mitchntx]

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

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

[AllZWay]

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.

[Fbody383]

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

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.

[Casey_SS]

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. choldway@yahoo.com
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.

[GlennCMC70]

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

That is a big negative Ghost Rider.

[Fbody383]

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

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.

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

That's why I asked.

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

[mitchntx]

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.

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

[Fbody383]

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

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.