1995 LT1 383 stroker troublshooting

[steiger99]

I have a 1995 LT1 with a 383 stroker (pretty much brand new) just installed. I have done pretty much everything possible to the fuel and spark system trying to fix this problem. My issue is this:

The car starts right up when it is cold. It revs very crispy and the throttle response is immediate. As soon as the car gets close to normal operating temperature, I have major issues. I think it is going into closed loop and I am not sure why. Once at about 180 degrees, the car start to bog down and run really rough. When I rev it or tap the gas it almost stalls out before it finally revs up a bit (almost like the gas being dumped in by the injectors is drowning the spark out. Eventually the car falls flat on its face and stalls out really hard once its warmed up. It wont start until it is cold again and then runs great until it gets hot again. (When it is warm and decides to stall out, black smoke comes out of the intake filter so something is causing that to happen.)

The car has a brand new MSD coil, new plugs, new msd wires, new MSD opti_spark, new injectors, new walbro fuel pump, adjustable fuel pressure regulator, compression checks out perfectly, fuel pressure holds strong at the 43 psi I have it set at, custom computer tune by Brian as PCMforless.com, new coil wire, TPS is adjusted to .67 volts and verified... The compression is 12.5 to 1 and it is setup to run on 94 octane gas. I have tried running 110 octane to see if it made a difference and it did not make a bit of difference. Stock MAF, stock MAP, stock ICM module, new waterpump... brand new o2 sensors.

Any ideas as to why the car is going into closed loop (if it even is) and stalling out when it gets warm? Why would it run so perfectly while it is cold and then just completely run like crap as it gets warmer?

What can I do to track down the issue here and fix this problem that is driving me crazy?

Thanks for your suggestions and ideas.

Steiger99@hotmail.com




What could be causing it

[bigrondownhiller]

The easiest way is to hook it up to a scanner and get a log of what is doing when it is warm. No reason to just start throwing parts at it.

[steiger99]

any idea of what type of scanner I would need that would give me the information I am looking for? Would it be a simple $100 scanner that you can buy at autozone or would I need to go to someone at a performance shop and use one of their $1000 scanners to diagnose something like this.

Sorry if this is a rookie question but I have been to 4 performance shops, including Livernois Motorsports in Detroit, and nobody has been able to diagnose the problem for me. I have already thrown every part known to man at this car so I am out of parts to throw at it.

Thanks again for any more ideas.

[5.0THIS]

A good GM tech with a Tech2 should be able to track down this issue.

[JaycenK]

Why are you using an adjustable fuel pressure regulator?

[Firebirdjones]

Didn't see any mention of 02 sensors.

I would assume those have been replaced too but that's the first thing that popped in my mind when you mentioned closed loop and running poorly.

In closed loop the 02 sensors become active in trimming the fuel. A fouled sensor, bad wiring, slow switching etc....any one of these should have thrown a code.
A scanner is your best friend.

[steiger99]

The o2 sensors are brand new (less than 20 minutes of run time on pretty much everything else I have just replaced and mentioned in the original post is brans spanking new as well). I will try to find a GM guy and see if they have the scanner I need. The car is not throwing any codes (no check engine light). I live in Brighton, MI and have been to the 5 performance shops within a 30 mile radius so if you have any suggestions on a good shop that might be able to diagnose this, please let me know. Thanks

[steiger99]

Why are you using an adjustable fuel pressure regulator?

1. Because it allows me to adjust the fuel pressure to the perfect setting... The car barely runs with the stock regulator so I went adjustable. I assure you this isn't the problem. I have done a fuel pressure test and the pressure holds strong overnight (by the 3rd day the car drops to 20psi but I'm ok with that because you will always have some pressure loss when the car is just sitting there like a paperweight, (at least I think ??)

2. Because chicks love adjustable fuel pressure regulators (Just kiddding)

3. What would be a reason not to have it if you had the choice between a non-adjustable and an adjustable?

[JaycenK]

1. Because it allows me to adjust the fuel pressure to the perfect setting... The car barely runs with the stock regulator so I went adjustable. I assure you this isn't the problem. I have done a fuel pressure test and the pressure holds strong overnight (by the 3rd day the car drops to 20psi but I'm ok with that because you will always have some pressure loss when the car is just sitting there like a paperweight, (at least I think ??)

2. Because chicks love adjustable fuel pressure regulators (Just kiddding)

3. What would be a reason not to have it if you had the choice between a non-adjustable and an adjustable?

Well everyone I talk to says stay stock and don't F' with it because it leads to problems that just can't be solved all that easy.
Again what in your setup requires you to run an adjustable regulator? Or is this just preferance?
Also have you had the tune checked? Who did the reprogram of the PCM?

[5.0THIS]

1. Because it allows me to adjust the fuel pressure to the perfect setting... The car barely runs with the stock regulator so I went adjustable. I assure you this isn't the problem. I have done a fuel pressure test and the pressure holds strong overnight (by the 3rd day the car drops to 20psi but I'm ok with that because you will always have some pressure loss when the car is just sitting there like a paperweight, (at least I think ??)

2. Because chicks love adjustable fuel pressure regulators (Just kiddding)

3. What would be a reason not to have it if you had the choice between a non-adjustable and an adjustable?

There are plenty of people running 383s with the stock FPR and stock fuel pressure settings. You either had (or have) a problem in the fuel system or in the tune if you require an adjustable FPR.

[steiger99]

The tune was done by brian at pcmforless.com. Then I sent it back to him to double check it twice after that. Could it really be the tune if the car runs so perfectly when it is cold?

Also, about the adjustable fuel pressure regulator, as long as I have the correct pressure set and the pressure is holding, isn't that what I want. Chad at Golenengineservice.com, (he built the motor for me), told me I definitely needed to have one so that is why I have one, no other reason. The fuel pressure is set to 43psi after the fuel pump primes. The priming pressure is 50 psi before it drops and holds at 43 psi.

I have a new fuel filter and ( a new in tank 'mini-strainer' that hooks to the bottom of the fuel pump itself), new 30lb injectos and I have checked to see if they are all pulsing correctly and they are. I am having a hard time believing it is a problem with fuel. I am leaning more towards a tuning issue if anything.

As far as tuning goes, doesn't the tuner program the PCM to match the motor specs and accessories and then that is pretty much all that car be done or is there a way to make changes to my PCM with a scanner if someone can find the underlying issue? Can you adjust the timing with a scanner tool or is that a preset setting in the PCM that once it is set, it stays unless re-programmed?

Thanks again for all the helpful ideas and thoughts, I wish I could find a place that has the ability to diagnose the problem. Anybody know if a good shop within 100 miles of Brighton/Ann Arbor/Detroit, Michigan area???

[JaycenK]

Have you tried starting the the car with out the o2's attached? If you have nothing to do verify all the primary O2 wires and make sure that they are all attached and not damaged. You really need a tech 2 so you can see what is going on when it runs good and then when it runs bad. As far as the FPR I don't know if that is it but isn't fuel pressure suposed to be like 50 60 psi? or am I having a brain fart and confussing my outboard motors fuel pressure here?

[Sleeper101]

I just done a lt1 Stroker for a buddy.

First off is the Tune. Im sure the guy tuning it is using lt1 edit as the tune Program?

2nd, he should be using a Wideband when Tuning the car If not then Take it to a new tuner b/c they cannot tune the car without it.

3rd If your tuner is using a wideband I hope he is not Just sticking it in the END of the tailpipe.

You NEED to get an o2 bung welded in the exhaust as SOON as both pipes combine into 1. This will give them the best a/f readings!

4th. DOUBLE AND TRIPLE check all Grounds on the motor. I highly suggest adding a few extra's. We had a MAJOR grounding issue's on this last one we done.

5th. With the LT1 edit software the tuner can watch the ignition system to see if it was breaking down.

6th. If you had a MAP sensor breaking down or even the MAF sensor breaking down. The A/f would show it on the wideband when Hot. The Tuner should be able to trace down that problem pretty simple if he knows what he is doing.

If he says he can't find anything wrong. Take it to a new tuner. Im telling you they CAN find that problem.

It really sounds like the ignition system is breaking down.

Check your plug wires VERY closely and make sure they have not gotten nicked or is laying on a header.

Hope this helps.

[heavychevyrider]

hey buddy i have a 95 caprice with the lt-1 and one older mechanic told me when running the 383 I would want to change maf sensors and put a cold intake on it because the car runs alot better with the much denser air. Not only that put you changed the compression ratio so you need to get more air in the vehicle. do you have a bigger throttle body and after market intake on it.

[camaro2000ss]

Have you tried starting the the car with out the o2's attached? If you have nothing to do verify all the primary O2 wires and make sure that they are all attached and not damaged. You really need a tech 2 so you can see what is going on when it runs good and then when it runs bad. As far as the FPR I don't know if that is it but isn't fuel pressure suposed to be like 50 60 psi? or am I having a brain fart and confussing my outboard motors fuel pressure here?

On a lt1 fuel pressure should be 41-47 psi (key on,engine off) and decrease by 3-10 psi (at idle).

[97bluebird]

I had pcmsforless tune my car too. All I can say is that it started and got me to a guy that could tune it. I basically wasted the $190 or whatever it was that I paid them. I got mine tuned by someone else and it was a night and day difference.