Hi guys,
I have a 95 Z28 that I'm completely stumped with. I've replaced everything I can think of. Fuel pump and filter, MAF sensor, TPS, IAC valve, injectors, spark plugs, water temp sensor, fuel pressure regulator, etc.
Its stalling under a load but runs fine in neutral and has a slight un-consistent knock at idle. Put it to the floor and it gains speed but just isn't running wide open like it should. I've taken the front of the intake off and soaked it in carb cleaner, blew it out and got it cleaned up. Replaced the injectors with 24# bosch d3's and has new bosch platinum spark plugs. Haven't tried the opti yet but I might. Even checked for vaccum leaks and couldn't find any.
Big thing is, is that its not throwing any codes and the ses light doesn't bother to ever come on. I've had several people hook expensive code readers up to it, both OBD1and OBD2, and they say error cant connect with vehicle. Idk if it could maybe be a bad pcm? Causing all the problems.
Any advice would be very helpful

 

Welcome to the site! I see you have a 95 z28, is it an automatic or manual? Do you have any mods to the car (cold air, headers, anything at all). Listing everything you have done to the car will help us diagnose it a little better. I see you have addressed the fuel issues with replacing pretty much the whole fuel system. Using a test gauge would be another way to test the system, making sure you are getting enough pressure to your injectors. Personally, i think this could be an ignition problem, as you said there is a knock at idle. A frayed coil wire would still bring spark to the plugs, but it would be a weak spark. That or a broken spark plug itself would cause some problems as well. Looking for arching at night with the engine running will help that as well. PCM's dont generally go bad like that, it sounds more like a sensor is giving bad information or there is something funny going on with the ignition. Since opti's are expensive and it requires taking apart the front of the motor to get to, its best to diagnose if that is going bad or not. At the top of the LT1 forum, there is a sticky that explains how to diagnose if it is good or bad.

I hope this helps alittle, take a look at the coil wire and at the spark plugs to see if there is anything off there. The optispark sticky will help determine if your optispark is the problem. then get back to us with that result and some more information about your camaro.

 

Problem with scanning it is the 95's have an OBD-1 PCM, but a 16-pin OBD-2 style ALDL connector. Shoebox shows you how to scan it with a 12-pin OBD-1 scanner:

http://shbox.com/1/xraycable.jpg

Obviously, if they hook up an OBD-2 scanner (which is the only thing many auto parts stores have), it won't connect. And, some of the newer OBD-1/OBD-2 compatible scanners will not connect correctly to the OBD-1 LT1 computers. There's a very old model Auto Xray OBD-1 scanner that will work fine. But the best thing to do is download a free copy of Scan9495, get a cheap cable and use that to pull codes, and run a data log of the engine operating under a variety of conditions. One of us can help you understand the data log.

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

Note that there are some codes that do not turn on the SES light, so absence of the light is not proof-positive that there are no codes. Just a check - does the SES light turn on for a few seconds when you turn the key to "run"?

Replacing all those parts without doing a thorough diagnosis is not the best approach, and will leave you with an empty wallet.

 

I have a spectre cold air intake, and a spectra premium fuel pump. Stock manifolds straight piped to an aftermarket muffler, not for sure what brand the muffler is. Eveything else is stock on the car. It has new plugs in it and I traced most of the plug wires and didnt find any bad spots or burnt spots. And no the ses light doesn't come on at all even when you just turn the key on before uou start the car. Automatic transmission

 

If your check engine light is not working, that is making it even more important to get a scanning solution.

 

+1 Need to scan the PCM and see what's going on. That is the first place I'd start. These cars (and I'm sure others) can have poor performance caused by a number of faulty components. The scan will point you in the right direction as to which faulty component.