Josh198816

Hello all. New here and have a friends lt1 trans am here. It's a 95. It will start if you pedal it to keep it going, randomly pops through exhaust and will die if you let off throttle. Changed plugs wires optispark coil and had to rewire tps. New aeromotive fuel pump. The optispark is the splined one. How would I go about diagnosing this as spark or fuel related.. When I rev it and drive it seems smooth doesn't feel like a misfire or anything. It's got me stumped here. He says it's 425 hp to the wheels but everything on it seems stock except a lingenfelter throttle body.. And by driving it to me feels stock. Any help would be greatly appreciated. Thanks in advance!

Injuneer

Splined drive (unvented) Opti was only used 93/94. 95 was the first year for the cam dowel pin drive (vented) unit. Has the engine been changed?

Hard start could be as simple as a faulty coolant temp sensor.

What does the fuel pressure prime to when you turn the key to "run" (not "start"), and how fast does the pressure drop when the pump shuts off after two seconds?

Josh198816

That's what got me. When I went to get the distributor I got the wrong one.

Coolant temp sensor is working according to gauge and my matco scanner. It runs like crap cold or hot no difference

I'll have to double check the fuel pressure again in the morning and see if it drops and how fast. I'll post the results in the morning.

Injuneer

But "runs like crap" only at idle? And this is ALWAYS the case, not just at startup?

Probably the best way to analyze the problem:

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

Free download, buy a cable.

Josh198816

Yes it's always the same. Not just start up not just warmed up. Always. I've got $3000 matco scan tool. No reason to buy that. But thanks for showing me that.

gaedbo

So what does your $3000 Matco Scan Tool say is wrong with your engine ?

Injuneer

OK.... sorry to insult your $3,000 scan tool, showing my ignorance. Do you have a data log showing vital sensor readings and PCM parameters, at least 5 frames per second that you can post? Or have you already analyzed that?

Just trying to help, if you actually want help.

Josh198816

Im getting ready to check fuel pressure and when I get that we can go from there. I can do data logs with the scan tool no problem. Its dealer level diagnostic. I'm used to working on European cars gm doesn't have near as much in the ecu diagnostic area so it's alot harder to see what's wrong.. I didn't think you were being insulting I just don't see the need to buy a cable to use free software I could be wrong though..

Josh198816

Lost the little valve in my fuel pressure tester. Didn't have time to grab another one today. I'll get it in the morning and if I can figure out how I may post a video of what it's doing so it makes more sense what I'm saying.. Thanks guys been alot of help so far

terminal_crazy

Coolant temp sensor according to guage is in drivers Cylinder head.
CTS for PCM is in water pump and not connected to guage in any way.
What does your scanner say for CTS temp?

Try cleaning the plug connector and wiggle plug/lead whilst scanning!

Mitch

Josh198816

The cts is reading same as gauge. I would have thought if that was the problem it would only do it warmed up.. Maybe I'm wrong. Fuel pressure key on engine off it primes to 50 then immediately drops to zero without turning off the key. Could that be the fuel pressure regulator? It's an aeromotive adjustable one. Already tried adjusting it and it doesn't hold the pressure.. Also I put in a new pump so I wouldn't think that would be the cause but anything Is possible..

gaedbo

Check the fuel pressure by turning the key to Run Without starting the engine. Fuel pump will run for 2 seconds then shut off. Pressure should be at least 40 PSI when the pump shuts off, and Hold.

I think I remember others having problems with the Aeromotive units. Are you using instructions that came with the unit when making the adjustments ?

Josh198816

That's how I tested it. It went to 50 as soon as it shut off it dropped to zero. It has aeromotive stealth pump and aeromotive adjustable regulator. Probably needs adjusted but it still drops immediately.. Could that be the cause of the way it's running?

gaedbo

To prove that it is not the fuel pump, you can do the following...

You can bypass the fuel pump relay and the SECURITY system interlock by supplying 12 volts to the fuel pump prime connector near the PCM. That will tell you if the pump is working.

Courtesy of Shoebox:

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

Josh198816

Ok. I'll do that first thing in the morning. I know when the pump is running I'm getting 50psi.. Is that test going to tell me if it's the pump or the regulator that's not holding the pressure? Something is bleeding it off.. Immediately after the prime cycle. Or maybe because we have too much pressure could it be running overly rich causing the popping out the exhaust and not staying running?