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Joe, ASE Certified Technician
Category: Chevy
Satisfied Customers: 7251
Experience:  ASE, electronics, Marine inboards and electronics, automotive drivability, all around repair tech,
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1991 Chevy truck 5.7 tbi. All of a sudden in the morning

Customer Question

1991 Chevy truck 5.7 tbi. All of a sudden in the morning truck would crank up and go dead after several attempts it would crank up run ruff then even smooth out , and also its idling up and down. OK change tps , map, tune up, coolant temp sensor, egr valve , idle control valve , fuel filter and pump.
Submitted: 1 year ago.
Category: Chevy
Expert:  Joe replied 1 year ago.


Thank you for allowing me to assist you, my name is Joe and I will be happy to assist you with your concern today.

You stated you changed the tps, did you use an gm part or aftermarket?

This year the tps sensor should not be adjustable I do not believe.

Have you watched with a voltmeter to see if the tps voltage is fluctuating?

Have you checked for air/vacuum leaks such as the iac, throttle body gasket and intake manifold gaskets?

Next using a fuel pressure tester (requires the in-line adaptor) check fuel pressure to be around 12psi and that it holds pressure, preform a fuel system leak down test. These are known for injector and overall tbi system problems. DO NOT change the spring for the regulator unless it is bad and only use an oem spring, the rest of the rebuild parts in the aftermarket kits are ok to use when rebuilding the tbi throttle bodies.

Thank you!
- Joe

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