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LT1 Not starting

Old 01-06-2019, 12:55 PM
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LT1 Not starting

Working on a project car and having some problems. It will turn over and wont start I have scanned it with no trouble codes.
So I started with the normal (spark and fuel) I'm getting spark but when I check the fuel pressure I get 40 psi when I turn the key on.
Now after the pump primes and it sets a few seconds the pressure will drop around 30psi or so. Is this normal or should I be looking for a leak?

I pulled the fuel rail off and primed it to see if any of the injectors are leaking and let it set for a few hours and they seem fine.
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Old 01-06-2019, 02:42 PM
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Re: LT1 Not starting

If it only drops to 30 PSI, and holds, should not prevent starting. Cycling the key quickly a few times before turning it to “start” will usually minimize the loss of pressure. Pressure loss can also be the result of a faulty check valve in the pump, a leaking fuel pressure regulator (check for fuel in the FPR vacuum line) or a leaking line, including the flex line in the tank.

Do you have a noid light, or a stethoscope to check whether the injectors are pulsing? Or if you still have the rails off, put a jar under each injector and BRIEFLY watch for injector pulsing when it’s cranking. Do that outside, no flames, minimum possible time, and have the proper extinguisher handy.

The PCM will not turn the fuel pump back on when you turn the key to start, unless it gets the fuel enable signal from the theft deterrent module.
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Old 01-06-2019, 04:15 PM
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Re: LT1 Not starting

I have to go out of town most of this week for work but I will try the noid light or the others when I get back home. Thanks Fred!!
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Old 01-12-2019, 11:47 AM
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Re: LT1 Not starting

I got some time to check it. I am getting power on the driver's side of the injectors but none on the passenger side. So I checked and swapped the fuses with no luck. So I guess it's time to dig into the wiring?
I used the noid light but with a test light I am showing power on the pink wires on the passenger side.

Last edited by chevyowner02; 01-12-2019 at 11:49 AM.
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Old 01-12-2019, 04:47 PM
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Re: LT1 Not starting

See if you can trace the pink wire for the driver side back to connector C100, pin A:

courtesy of Shoebox

http://shbox.com/1/1995_pcm3.jpg

1995 Z28 A4 Engine Harness



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Old 01-12-2019, 06:39 PM
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Re: LT1 Not starting

What kind of test light was used? If it isn't a low-resistance one, it may not help. Leave it connected while the engine is cranking. It should not flicker.
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Old 01-13-2019, 11:18 AM
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Re: LT1 Not starting

Originally Posted by GaryDoug View Post
What kind of test light was used? If it isn't a low-resistance one, it may not help. Leave it connected while the engine is cranking. It should not flicker.
It was a low resistance but I took a meter to the pink wires today and I'm getting 12.1v at every one of them. But when cranking the car over it drops to around 9v.

Last edited by chevyowner02; 01-13-2019 at 11:31 AM.
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Old 01-13-2019, 01:28 PM
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Re: LT1 Not starting

Originally Posted by chevyowner02 View Post
It was a low resistance but I took a meter to the pink wires today and I'm getting 12.1v at every one of them. But when cranking the car over it drops to around 9v.
OK then, that seems to be a problem. It should remain at 12v even with the injectors working. I suspect a bad connection somewhere for the 12v. Compare it with the pink wire on the other side while cranking.
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