someone please help me fix my LT1 !!!!!!!!!!!!!!!!!!!

[PewterPan]

my 1995 z28 is a real pain in the ass. my mechanic and i have been trying to fix it for months now. it has a new coolant sensor, distributer, and its been tuned, but still no luck. there are two major problems...

the first problem is that the engine doesn't start when its cold. it cranks and cranks, but it almost never fires. however, sometimes after its been cranking for a real long time, it fires and drives absolutely fine! oh and here's the kicker...it will restart after its been running. there is a catch though, it seems to be drawing power from somewhere because whenever i try to start it again, i can hear the starter cranking super slow and the the interior lights dim. (btw, its been plugged into and the computer reads that everything is fine with it and the computer itself is good.)

the second problem is that whenever the car is running and i try to rev it, the engine chokes and lags before the rpms go up.

DOES ANYONE HAVE AN IDEA WHAT MAY BE WRONG WITH IT?!?!

[kyleozzie]

fuel issue maybe? i know my main fuel line in the take got a hole in it and did the same thing, would take along time to start then when running really doggy because it was leaning the motor out.. but i guess the easiest thing would change the filter first? its like 10 bucks lol.. hope this helps.

[JoeliusZ28]

yea, im with kyle check your fuel pressure. When my pump went bad my car would crank for 5-6 seconds and eventually wouldnt rev up anymore.

[MP81]

I'm guessing fuel pump.

Check the fuel pressure at the rail - should read around 46 psi. When the one in my '86 went bad, I'd have to crank for about a minute straight - when I did a pressure test, it had 3psi at prime.

I have a gauge if you need one to borrow, btw.

[PewterPan]

I'm guessing fuel pump.

Check the fuel pressure at the rail - should read around 46 psi. When the one in my '86 went bad, I'd have to crank for about a minute straight - when I did a pressure test, it had 3psi at prime.

I have a gauge if you need one to borrow, btw.

i doubt its anything to do with the fuel system because it runs great...when its running. lol. im thinking that its something electrical, but idk what it could be. maybe its a bad ground or sensor? are there any sensors that are notorious for going bad on these cars?

[MP81]

Mine ran fine when I got it started.

Do LT1 cars have fuel pump relays? Can you hear the pump prime?

[PewterPan]

Mine ran fine when I got it started.

Do LT1 cars have fuel pump relays? Can you hear the pump prime?

yeah, i can clearly hear it working. i also know that its getting spark because i have new wires and a new distributer on it. my mechanic thinks that its a bad ground somewhere. he also said something about a so called "map" sensor.

[2EVUL4U]

Had a similar problem right after I installed my 383-LT1 ... I modified the TPS, so the signal sent to the computer was the right voltage. Haven't had a problem since.

[JoeliusZ28]

i doubt its anything to do with the fuel system because it runs great...when its running. lol. im thinking that its something electrical, but idk what it could be. maybe its a bad ground or sensor? are there any sensors that are notorious for going bad on these cars?

nope, i still say fuel pump. When i had low fuel pressure I was still clipping off 12.90s at the track. I didnt believe it either until MP81 lent me his pressure gauge out at woodward.

[PewterPan]

ill ask my guy and see what he says. im still a little skeptical though. yeah, i guess it would make sense because the problem gradually got worse and worse, but idk.

[MP81]

I mean, it literally takes 5 seconds to check, so why not have it checked.

[JoeliusZ28]

ill ask my guy and see what he says. im still a little skeptical though. yeah, i guess it would make sense because the problem gradually got worse and worse, but idk.

mine gradually got worse too. began with hard starting and progressed to starving to the point of not being able to do any more than idle.

like kyle said its easy to check.

[meissen]

It's DEFINITELY the fuel system and it makes COMPLETE sense with your 1st problem. The fuel pump holds fuel pressure for a couple hours - I think it's only supposed to bleed off like 1PSI per hour or something like that. If your car starts immediately after running it's because the fuel system is still pressurized and you still have fuel easily available at the fuel rails. The reason it won't start after it's been sitting/cold is because the fuel pressure has bled off and now you have to pressurize the system again. Makes perfect sense.

Check your fuel pressure regulator. It's behind the intake manifold on the fuel rail - big cylindrical object with a vacuum line going to it. Remove the vacuum line from the FPR and smell for gas or check to see if it's wet inside. If it is, your FPR is bad and that's your problem. With the vacuum line still off, turn the car on and it *SHOULD* be idling at a higher RPM. While it's still running, plug the vacuum line back in and your RPMs should go down. The FPR is vacuum controlled so when there's no vacuum (IE: wide open throttle), your FPR should be letting more fuel into the rails and thus higher RPMs.

Here's a pic of the FPR:

[PewterPan]

so, it turns out that the fuel pressure and everything else is fine. my mechanic checked it out. you guys got any other suggestions? lol

[meissen]

What did he say the fuel pressure checked out at? Did it hold pressure after turning the car off?