'94 Cold Starting Problems

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Jun 24, 2008 | 10:51 AM

DeanRM

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'94 Cold Starting Problems

I have a '94 LT1 6-spd, and it starts hard after sitting for a few hours. It will start right up after it has been running.

I checked the fuel pressure, and that is over 40 psi while running, and it will hold the pressure after I shut it down for at least 30 minutes.

The engine cranks over real fast for about 10 seconds before it will fire, then it stumbles a little, then smooths out and runs great. Sometimes I can smell gas a little while cranking.

Any suggestions?

Thanks!

Jun 24, 2008 | 12:11 PM

FICINJECTORS

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From: Cumming Ga

Quote:

Originally Posted by DeanRM

sounds like you have to do more leakdown checks. You say it holds for how long after shutdown? It will probablly always start when the is pressure in the rail. Check that. When there is little pressure does it then start hard? If so, you have and injector or the FPR leaking.. Isolate the leakdown and post further info.

Jun 25, 2008 | 09:02 AM

DeanRM

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Ok, I did a leak-down test last night. As soon as you shut it off, it is about 38 lbs. After 30 minutes, it is 15 lbs. After an hour, it was about 8 lbs.

It starts hard when there is little pressure. How do I check the injectors and the fuel pressure regulator?

Thanks!

Jun 25, 2008 | 09:37 AM

94z07fx3

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Quote:

Originally Posted by DeanRM

How do I check the injectors

You can hear them fire with a mechanic’s stethoscope. You can verify they are getting a pulse with a noid light. You can see the magnitude and duration of the pulse with an oscilloscope.

Quote:

Originally Posted by DeanRM

and the fuel pressure regulator?

A simple test is to remove the vacuum line to it, carry it away from the car, and sniff for gas. A strong smell of gas or visible wet gas is a likely sign of a failed FPR diaphram.
Another test is to watch fuel pressure and RPMs together. Fuel pressure should rise with RPMs.

Jun 25, 2008 | 10:04 AM

FICINJECTORS

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From: Cumming Ga

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Originally Posted by 94z07fx3

You can hear them fire with a mechanic’s stethoscope. You can verify they are getting a pulse with a noid light. You can see the magnitude and duration of the pulse with an oscilloscope.

A simple test is to remove the vacuum line to it, carry it away from the car, and sniff for gas. A strong smell of gas or visible wet gas is a likely sign of a failed FPR diaphram.
Another test is to watch fuel pressure and RPMs together. Fuel pressure should rise with RPMs.

1st do the sniff test on the vac hose from the reg. But, a regulator could be leaking through the valve inside to release pressure. The hose test is for when you have a torn diaphram. You can check your injectors on an LT1 pretty easy. first clean the manifolf where each injector seats. next remove the pressure (if any) from the rail by pushing in the schrader valve. Then remove the 4 bolts that hold the fuel rail to the manifold. Lift the rail with the injectors out of the manifold and hold the rail high enough to visually see the bottom of the injectors. Now have someone turn the key to on and pressurize the rail. DO NOT CRANK THE ENGINE. If an injector is leaking you will see it drip. A slight drip is all you need to release rail pressure. Your pressure is not droping fast so take your time. Usually a bad FPR diaphram will leak quickly. This whole thing takes a half hour.
If the injectors dont leak. lube the bottom o rings and reinstall in the manifold. start looking at the fuel pump and regulator.

Jun 25, 2008 | 10:20 AM

DeanRM

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Thanks alot guy's. I will work on this tonight and let you know what I come up with.

Jun 25, 2008 | 10:31 AM

94z07fx3

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Quote:

Originally Posted by FICINJECTORS

...lube the bottom o rings...

What lube do you use for nitrile (Buna-N) o-rings?

What lube do you use for Viton o-rings?

Jun 25, 2008 | 11:11 AM

FICINJECTORS

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From: Cumming Ga

Quote:

Originally Posted by 94z07fx3

What lube do you use for nitrile (Buna-N) o-rings?

What lube do you use for Viton o-rings?

i use dish soap (palmolive) on all the rings.. soap does not leave any residue on the o ring. Just a preference. Viton can withstand any lube, Buna will dry up using lubes with certain chemicals. so stick with the soap.