Sounds like your mechanic is right about addressing DTC 300 before worrying aout 132/152. The section on DTC 300 (page 6-450, step 2 of the action table) states "Important If any DTC are set (except DTC ...132...152...) refer to those before proceding with this diagnosis."

I gotta read the FSM better.

Eric

 

Knowing all you've been through on the car... I just honestly don't think the PCM is the cause if the problem... maybe the tuning of the PCM, but I think a defective PCM is an issue. My car had the same shuddering you saw tonight even with the stock PCM after the hotcam went in.

What it could be Im' at a loss for thou at his point...

 

Wow, sounds alomst like my problem.
I would be very interested to hear the solution.
I have a stock L98, and while cuising at 2k rpm or less when its 60 degrees or less I get a stumble and SES light for a few seconds. If I push the throttle, the problem goes away.
The issue never seems to happen when its warm out.
replaced tps, maf, wires, plugs... Seriously considdering a crate motor at this point.

 

I swapped out back to the Ed Wright PCM and no change. His program apparently turns off ALL misfire detection because I see nothing like with the other PCM. I even pulled off one of the plug wires and it still showed no misfire!

 

Well I'm gonna go out on a limb here and say that it's not cause by the Hot Cam directly. Mine has given me some odd driveability issues but never to the extent that you have described. Also I just installed heated O2 sensors and the car behaves MUCH better with them. I had some really bad misfire crap once, but it was accompanied by all of my gauges going crazy, this was the ECM. I can't see you having 3 bad PCM's there, so I really don't know what to tell you. I would be inclined to agree with whoever mentioned it that it may be a wire got burned on the headers.

I feel your pain man, I hate stupid problems like this, they are the hardest to find. Best of luck :cheers:

 

In the thread title, "Closed loop" is specifically mentioned. That begs the question of how does the car run during initial start-up while it's in Open Loop?

I had a '90 L98 that exhibited similar symptoms. Ran fine/idled fine during Open Loop. As soon as it went to Closed Loop, the idle went to poopie and I'd get bucking/stumble during cruise. Turned out to be a couple bad injectors. The real kicker is that the injectors tested good when cold. They only tested bad after running for a couple minutes.

Just one of those odd-ball / darn near impossible to find problems I thought I'd mention.

 

I thought I mentioned this before but I apparently did not. The problem now exists all the time closed loop or otherwise except during acceration. This board is not the only place I posted this problem.

Sorry for the confusion. I just bought some new plug wires and will try them out. They are a inexpensive next step I guess. :rolleyes:


[Modified by ericcer, 4:55 PM 11/29/2002]

 

Where can you get a new ecm for $90.00??

 

I can get a new PCM for mine for $115. There is a $200 core.

Jason Cromer
Sam Taylor Buick Cadillac
329 Miracle Strip Parkway
Fort Walton Bch, FL 32548
1-877-726-8295 http://www.samtaylor.com

I get all my parts from them. No one can beat their prices and there in my state so shipping time and cost is minimaul.

 

Have you worked through the action table for DTC 300 (page 6-450)? That would be my first step to investigating this problem. Step 3 (for multi cyclinder misfires) addresses several systems that were removed/reinstalled when you put in a HOT cam. I have my doubts it's the PCM since both banks have the 132/152 DTC.

Eric

 

Had a similar problem just last week. It was getting progressively worse for about a month. Turned out that the O2 sensor's pigtail connector got fried on a the exhaust pipe. I replaced the O2 sensor with the AC Delco brand (had Auto Zone in there) and it appeared to temporarily correct the rough idle, surging at cruise, near stalls at idle etc. The problem came back two long trips later. I took a shot in the dark and replaced the weatherpack connector that the O2 sensor connects to and for the past week the rough idle, near stalls, and surging have dissappeared. I'm glad that did it because my next guess was going to be fuel pressure and fuel related fixes. Good Luck!!!

 

Changed plug wires and no different. I looked at the O2 wires and they don't look burned.

As a side note, my mechanic used a Tech2 to test things out. That is when he saw misfies all over the place but zero on acceration with the PCMforless PCM. The Ed Wright PCM I have in the car always will read zero misfires.
Is a Tech2 going to give a true reading or is it reading from the PCM just like Autotap?


[Modified by ericcer, 1:26 PM 11/29/2002]

 

This weekend I added an adjustable fuel pressure regulator (played with various psi), new plug wires, swapped MAF, fuel rails with injectors. The problem is still there 100%

Tomorrow, off to the local Corvette mechanic again.

[Modified by ericcer, 6:32 PM 12/1/2002]


[Modified by ericcer, 6:33 PM 12/1/2002]

 

What brand o2's?

 

I have tried my original Delco, new Bosch, new OEM Delco. AutoTap shows them jumping around (mv values) at idle like they are suppose to.

 

possibly a bad vacuum leak somewhere?

 

I've known of a couple & also read of many LT series cars that have had problems with the Bosch 02's. The cars exhibit the exact problems you describe. When the Bosch's are removed & replaced with the AC/GM units the problem often goes away. Not all of the people/cars that use the Bosch have the problem. o2's operate at very low millivolts, I've always suspected it has something to do with quality control issues during the manufacture of the offending o2's. I would suspect variance from lot to lot. It appears you have covered that base though. Just a thought.

 

along that line of thinking...

a friend of mine has a 95 Z-28 that once upon a time gave him a horrible fit trying to run. We just knew it was the opti but replacing that wasn't the problem. We replaced almost everything on the car except the O2 sensors. Finally we decided to replace those, and we also bought an A/C recharge kit. We changed the O2's and fired it up, sure enough it was still stumbling and acting all kinds of stupid at idle.

We said screw it and just wanted to see if the A/C recharge kit would work. We started fooling with it, engine running, and by the time we finished with the A/C the engine was running smoothly. We were like WTF? Took it for a test drive, worked like a charm. Turns out it was the O2's all along but the computer had learned so much bad info from the faulty O2's that it had to re-learn with the new ones.

 

Very good point, have you been resetting the PCM by disconnecting the power for awhile after swapping parts. It takes time for the short term integrators to correct the long terms. I believe there is a time something like 30 minutes, you are supposed to leave the power off for? Not sure of the exact time. :iagree:

 

I resealed the intake and cannot find a leak. Howerver, I have not put a vacuum guage on the car.

Last time I reset the PCM was when I replace the plug wires this weekend. I did not do for the fuel rail swap and only drove it for about 5 miles.

I spoke with a experienced speed shop guy this weekend and he said I should of glued the optispark rotor on even though it was new. He even pulled out a aftermarket instruction sheet that mentioned that you should do that when replacing an opti. He has had some odd experiences with the optisparks. I have read about problems that are the reverse of mine. In other words problems occur with load/acceleration. All I can think of is to replace the opti again. It is under warranty so It is a day job for me.

I can say that this problem is really a cutout not a stumble. It sure feels like electrical. I forgot to menetion that I hooked up a timing light gun to each of the plug wires and it flashed light on all of them.

Just got back from the mechanic and he pointed out the my coil was buzzing. That is an indication that it is being overworked. I told him I have NGK TR55 in there with the standard gap of 55. He thought that was to much and suggested 35. I will be done that tonight. I thought I read that many of you guys running these plugs with the unmodified gap of 55.

[Modified by ericcer, 7:03 AM 12/2/2002]


[Modified by ericcer, 11:39 AM 12/2/2002]


[Modified by ericcer, 11:40 AM 12/2/2002]