Need help with highway cruise problem

[Pacific_L36]

Got a 1996 3.8 Camaro, with a 97 pcm. When I'm on the highway holding steady throttle, it'll suddenly peg my WB rich or lean (random). If I let off the gas, or bump the throttle just a bit, it'll pop back to where it should be, but not for long. On occasion it tries to die, or looses power as a result of this. In the case of pegging rich, I'm told that it starts blowing a gas cloud out the tail pipes. This problem has been around for a long while, during the duration of this problem I got rid of the cat, and unplugged the egr (made all necessary adjustments for this I believe). Driving around town is fine. I'm entirely lost on this problem. Another person on another forum is having the exact same problem, he figured out that if you force open loop (by setting the CL enable temp high) that it runs fine, no problems. He also said the he replaced the MAF, MAP, 02 sensors, PCM, and several other items to no avail. I tried forcing OL myself, and got the same results as he did. Both cars have 97 pcms, the difference is that his has a holden intake conversion vs my engine is still bone stock, same exact problem with both.

Is there a hidden table in HPT that I can't see possibly? I have HPT pro and an AEM UEGO WB plugged into it. I really need help with this problem, this is my main source of transportation.

I have attached a scan and the tune to go with it, this is before I learned about forcing open loop.

[Perforator]

Maybe a CAT test? I know some people on the GP board found a problem with some years where if you removed the rear 02 sensor it caused the PCM to continually run these CAT tests that commanded funky af/ratios.

[Pacific_L36]

I've got 4 o2 sensors, 1 in each header, and pre-post cat. The pre o2 has been removed to gain a bung for my WB, the post is still in there. But I had this issue before I touched any of that, so I don't think it's the issue.

[Perforator]

What was the last thing you changed before it started happening?

[Pacific_L36]

I believe it started happening the first time I touched the pcm. It originally came from pcm4less, and never ran right ever since I installed it. That sparked my purchase of this software and the wideband. But pcm4less flashed my 96 vin into the pcm, so I couldn't tune it. What we ended up doing was finding a complete 97 stock auto tune, did a write all, and I zeroed out the tranny tables (have a manual). Ever since then it's done this weird thing on the highway. And now that I think about it, we shut off all the dtc's for the soon-to-be deleted cat and egr when I did the write-all.

[Pacific_L36]

I looked up the Cat test you told me about, and enabled all the factory o2 codes, but set them to not light the mil. Seems to have fixed it so far, I'm gonna drive it some more before I start counting my chickens.

[Perforator]

Sweet! Let us know if that did the trick.

[murphinator]

COT = cat overtemp protection

my understanding is it runs a test every so often where the pcm dumps fuel and monitors the difference between front & rear 02 sensors to make sure the cat is doing its job

double check your COT settings in the engine tab , nobody from hpt can give advise on it because to get around it your defeating an emmisions device

if you have no cat you dont need it running this test so set parameters that will never be achieved and the test will never happen

[Pacific_L36]

COT isn't the cat test, completely different judging from what I've been reading. I have it disabled also.

[GTPNoga]

I had this same problem. Let me find the post, at one point the PCM was commanding 16.4 AFR..

http://www.hptuners.com/forum/showthread.php?t=17538