1991 Chevy S-10 Will not start when cold

WUKONG

MEMBER
1991 CHEVROLET S-10
4 CYL
2WD
MANUAL
174,000 MILES

My S-10 will not start when cold. It will start if I prime by pouring a small quantity of gas down the TBI. When warm it will start without the prime of gas. I can shutdown and shop for 10 to 15 min and it will restart. When I leave it for an hour, it will not start without priming. In the past I experienced this problem if I did not start it for a period of several weeks or on cold mornings. The symptoms would be stalls during cranking and muffler pops.

I have replaced the fuel pump, fuel pump relay, and the fuel pressure regulator.

Can someone help me locate the source of my problem.

5 Replies

RACEFAN966

MECHANIC
5,029 POSTS

Have you replace the fuel filter? Have you checked the fuel pressure when it won't start?

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Friday, February 5th, 2010 AT 9:41 AM

WUKONG

MEMBER
3 POSTS

I have not replaced the fuel filter and I have not checked (or know how to check) the fuel pressure. I did replace the fuel pump so I assume that a fuel pressure is not the problem.

If it will start and run after a bit of gasoline down the TBI, could there be a fuel pressure problem?

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Friday, February 5th, 2010 AT 11:15 AM

RACEFAN966

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Well it could have a problem with pressure when it is cold. It is throttle body injection so it could also be the fuel filter sense the fuel pressure is lower then multi port injection. Your fuel pressure should be 9-13psi. So if you would change fuel filter and then check fuel pressure when it is cold and lets see what it is.

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Saturday, February 6th, 2010 AT 8:41 AM

WUKONG

MEMBER
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I will somehow try to get a pressure check somewhere.

I just replaced the fuel filter and I loosened the B-nuts on both fuel lines at the TBI individually and got gushes of fuel. I did this while jumping the orange and brown/white wire at the fuel pump relay. With my jumper is in place I can hear the fuel pump run.

With the jumper in place the engine will not start with out a prime. With a prime the engine will start and run normally.

When I remove the jumper and reinstall the fuel pump relay, I do not hear the pump run with the ignition in run and the engine will not start. When I prime the TBI the engine will start.

One significant difference that I noted today is that with the hood up the engine would not start after shutdown when warm. In the past it would start when the engine was warm with the hood down. I'm going to go and refuel and check to see if it will restart warm with the hood down.

Under the front of the air filter housing are two small plastic tubes. One of the tubes runs to a sensor that has three wires connected to it and this sensor is attached to the Air Filter housing. The other tube is longer and wraps around to the rear of the air filter and is not attached to any device that is clearly visible. I have yet to find any device to connect with this tube. Can you tell me where to connect this tube?

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Saturday, February 6th, 2010 AT 2:30 PM

RACEFAN966

MECHANIC
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That tube goes to manifold or constant vacuum from the engine as that sensor is the map sensor. This could be the problem but get vacuum to it and see what it does.