SO i had a terrible running 1995 LT1. At first i noticed when driving the pitch of the exhaust went lower and not near as crisp, sounded muffled, then it sounded like it was down a cylinder when i hit the gas. It made that muffled acceleration noise. So i changed the Opti. Brand new GM top one from rock auto. I also changed the 2 top oil seals and water pump and ignition coil. After putting it all back together i cranked it up and the car sounded better than ever, very crisp clear throttle response, the best its ever sounded. That lasted 5 minutes, back to all the original symptoms, exactly the same. Its still all assembled. Im thinking bad opti. Any other suggestions?

 

Did you check for a plugged cat (if you have one)?

Did you do any diagnostics on the first Opti to verify it was defective?

 

I've seen a lot of problems caused by burnt plug wires or something that's easy to check. It's just an example of where someone replaced expensive parts without knowing for sure they were the problem. Make sure to eliminate cheap fixes before jumping to the expensive stuff. Getting it checked for codes may help solve the mystery.

 

Thank you for replying. No i did not diagnose the old opti, i will when i learn how over the next day or 2

 

I agree with what your saying. The new opti did make a big difference for the 5 minutes it was running good, there was a clear obvious difference. Also, the old one was packed in oil. The opti i took out was one of the yellow backing ones, and i couldn't see any yellow with all the oil on it. i have no leaks under the car now, it was leaking bad. So im glad i changed it.

 

Since it ran better for a few minutes until it warmed up, the cause may be related to the PCM transition from open loop to closed loop. That may point to an O2 sensor problem.

While it would be useful to check the Opti-to-PCM-to-ICM integrity, using Shoebox’s procedure….

4th Gen LT1 F-body Tech Articles

….. it may also be useful to run a PCM data log and gain insight to what's going on:

https://www.camaroz28.com/forums/com...95-lt1-874306/

If you can generate the log, I can help you interpret it, and look for problems. Here's a recommended driving procedure to produce a more useful set of data - see post #2:

https://www.camaroz28.com/forums/com...-guide-886891/

Note that post #1 has a download of a guide to understanding the data available from a log.

I will caution that assisting with interpreting the data log may take a while, because it seems like at this point, I'm the only one who is willing to spend the time, and there can be a waiting list.

 

I will do this and get back to you. Thanks for the replies so far.

 

It sounds like the running bad issue could be from a bad O2 sensor if it only runs good in closed loop. Does the vehicle set a code for a bad sensor? I'm also wondering if starting it cold a couple times and see if it runs great until it goes into closed loop would also indicate a bad O2 sensor or could other things be the cause? Looking for ways to diagnose this without doing a datalog for people without the ability to do one.

 

If you determine the opti-spark is bad contact Petris Enterprises. If he does not have available distributor then expensive MSD. I had an MSD installed for 10 years with no problems until a few months ago. SEnt to MSD to have rebuilt, $150.00, but it was going to take 1 month or two so I ordered one from Petris. I now have a backup if I ever will need it. Call first and discuss what you have if you decide on Petris

https://petrisenterprises.com/

 

My 97 had original O2 sensors in it at 150,000 miles when they started throwing codes. First was driver's side upstream. I ended up replacing all 4 but never had the same issue you have. I'm not saying a bad O2 won't cause that problem. They really don't last more than 100k miles so surprised they lasted that long. Stick with ACDelco if you replace them. My car has been a Texas car its whole life, might have something to do with it.

I now have a Petris opti. Original at 153,000 was still running fine so it's a spare. Also replaced ICM, coil, wires and plugs just because. Didn't have ignition issues, believe it or not, my reasoning was preventative maintenance. Also sent the injectors to be professionally cleaned, turns out they needed it. All this was done recently. Car sat on jacks for 4 years until a couple of weeks ago.

 

I have a file now. I have a file named "DLOG-Save-2021Dec13-172854-2G1FP22P3S2188132" Would you like me to email it to you?

 

Attach the file to a post right here.

 

I uploaded a file.

 

I'll download and take a quick look. I've got one person ahead of you who's been waiting since befor Christmas.

 

All good. Thanks for the help so far.