SKmaroZ28

Hello. We are Sean and Kathy. We have a 1994 Camaro Z28 LT1.

We are new to posting but not new to reading the forum. We have been trying to troubleshoot this car for 2 years now. The first project was the transmission. We noticed it slipping and instead of waiting for it to go out we replaced it. A few months after the main bearing went out, lost oil pressure and stopped the car before the motor seized. We bought another engine last spring and replaced it. We bought new parts where needed and did not do any modifications. Everything is stock. The car ran well for a little while then we noticed that it was hesitating on acceleration and was running rich. We have been trying to troubleshoot it since. We checked the fuel pressure and it was steady at 40 psi. It has had very few miles, probably less than 200, and we can't seem to figure it out. We are afraid to drive it too much and cause more problems. We have talked to several mechanics but most don't know much about the LT1. We recently bought a cable and downloaded Scan94/95 so we can see what the computer sees. The problem now is we can't find much information to what the normal parameters are for a stock motor. Most on this forum and others have done mods so it hasn't been very helpful. We did finally take the opti off last week, we had just replaced it in the last year but had to go cheap at the time, and when we took it apart it was definitely made cheap and was bad. I won't go into details about that now. We won't do that again. We put on a new opti, MSD vented. Yes it is for a '94 but modified to be vented. We do know that the '94 LT1 is "special". We also replaced the water pump because we noticed a leak. That was not affecting the performance as it wasn't leaking bad enough to make it hot but it did leak on to the opti. Anyway, we got the car put back together and she started right up. Ran great!, til she got to operating temperature. In park the hesitation at 1300-2300 rpm's and popping through the intake. We are at a loss. We don't know where to go from here.

We need someone to look at a scan for us that knows LT1's. What are we missing? We don't want to start just throwing the parts cannon at it either.

I am posting this today to see if anyone will respond. I don't have access to the scan we already did until tomorrow, but that was before replacing the opti so I'm guessing we should probably do another. We did scan it last night after replacing the opti but the car was in park. What I could see was that there were no changes from the scan before the new opti to after the new opti. They appeared to be the same, but as I said we are not quite sure what to look for either.

Questions....

What type of driving is needed to get a good picture of what the car is doing?

How long should the scan be?

Does it make a difference if the car is going down the road or in park?

Please, if anything is unclear just ask. Any and all help will be appreciated.

Thanks,
Sean and Kathy

parkers Z28

are the plugs and wires in good shape .... When its dark outside look for any arching from the wires
Did you use lock tight when replacing the opti ?
Are you sure you installed the opti correctly ? I'm assuming you did since this was your second install however lots of people get it wrong
Water is very bad for the opti !!!
clean opti wire harness connections
Do a search on here for shoebox click on the link in his signature.

SKmaroZ28

Yes we used lock tight.

Yes we made sure the opti was installed correctly. This is the 4th or 5th opti, lost count, in 3ish years so not a new repair experience lol.

Yes water is very bad for the opti. That is why the water pump was replaced.'

It's been checked and cleaned. The new opti came with a new wire harness.

We have been on Shoebox many, many, times. It's bookmarked.

So it's not the opti. Any other suggestions?

Thank you.

parkers Z28

If one of the resident experts don't come along post this in the LT1 section
sorry I'm not much help but I'm no mechanic Lol.
there are some guys on this site that REALLY know there stuff
have you checked the ICM ??

SKmaroZ28

That's what I'm hoping is that someone can point us in the right direction. I'll check in the morning and if there is no response I'll move it. We weren't sure where to start and figured this was as good a place as any.

Pretty sure the ICM has been checked. There have been so many checks and rechecks it's hard to keep it all straight lol. We have checked and rechecked everything electrical and then some.

Thanks for the input.

Injuneer

Let's move this from "New Member Intro" to "LT1 Based Engine Tech", where it will get the attention it need.

Injuneer

To run a scan, do NOT reset the PCM before the scan. Start the car cold, let it warm up at idle, long enough to go into closed loop. Typically, you want the coolant temp above 140*F and the open loop timer to time out (206 seconds). Do not play with the throttle while it's warming up.

Then drive the car normally, with a wide variety of throttle positions and RPM. If you know you have a problem in a specific RPM range, try and replicate those operating conditions, hoping the problem will show up. At some point, do a full throttle acceleration from a low MPH roll, taking the engine near redline (5,800 RPM) in one gear. At the end of the log, park it, let is idle for 30 seconds and shut it down.

Upload the competed data log to an FTP site, and post the address here in this thread. There are several of us who can look at the data and see if the problem is apparent.

I have a 26 page writeup on interpreting the LT1 scan data. I can send you a .pdf file via e-mail.

SKmaroZ28

Fred, Thank you so much! Finally a place to start.

I will be leaving work here shortly and I will do the scan as suggested.

I would greatly appreciate the .pdf file for interpreting LT1 scan data for now and for future use.

Again, thank you so very much!

BTW I forgot to mention that there are no DTC's. The last DTC was for an O2 sensor and that was replaced with AC delco parts.

Injuneer

Please send my you e-mail address in a "Private Message". Alternatively, I can use the e-mail you used to sign up at this site, but I have to use the Moderator screen to access that. The e-mail we can send by left clicking your screen name does not allow attachments.

97WS6SCharged

Not sure if Scan 94/95 can export the data but if you can, upload a copy of the scan in .CSV format.

Injuneer

Scan9495 produces a .csv record of the data. Very easy to work with.

SKmaroZ28

I did a scan yesterday and I could not duplicate the problem....which is a good thing. The car ran great!

I don't have the data log on this computer so as soon as I get it emailed to me I will post it here. Hopefully sometime today. I would still like someone to take a look at it just to make sure everything is doing what it should or if we need to be aware of something that may go wrong and we won't have to pull our hair out anymore.

We do have some questions about the car for a better understanding....

Does the PCM need to "learn" after replacement of a part, motor, transmission etc.?

We do have other questions but I will wait for those when I post the scan since they are more related to that.

Thank you for the quick response and assistance.

Injuneer

The PCM doesn't learn a whole lot. Primary function is to learn the fuel corrections required over a wide range of RPM and engine load (MAP), to keep the A/F ratio at 14.7:1 where the combined emissions (CO, HC and NOx) are minimized. It also learns the idle air control setting for starting, and will retard timing long term in response to extended use of low octane fuel. If you "reset" the PCM by pulling the power, you lose that learned data and it will need to be relearned.

Replacing most hard parts will not affect A/F ratio, IAC counts or the low octane toggle.

There may be some adoptive learning related to the 4L60E trans, but I'm not familiar with that.