1990 Chevrolet C2500 Idle Surges and Floods Out

Reader Question: I have a 1990 Chevrolet C2500 5.7L fuel injection truck that has started having starting problems. It does not start as it used to (or starting at a fast idle and then slowing to a slow idle), then as it warms up it starts flooding out.

I thought maybe it could be an oxygen sensor, but I can find none on the exhaust manifolds. Is this my problem? If so, where is the oxygen sensor on this truck?


Hey Brian,

I’m not really sure what to tell you to do with this issue, except get a mechanic to read your computer codes and hook up a hand scanner to see what is happening. You did not mention anything about the check engine light coming on, or the engine dying unless the flooding out part causes the engine to die.

I would want to also hook up a manual fuel pressure gauge on the engine itself to see what fuel pressure from the pump is doing. This sounds like a lack of fuel pressure/delivery problem to me.

You probably do not have an oxygen sensor problem, but could have an issue with the coolant temperature sensor, the fuel pump, MAP – Manifold Absolute Pressure sensor or maybe just a dirty throttle body. You might want to clean your throttle body (or pay a mechanic at a fast lube place to do it for you) and see if that helps.

Here is more about the throttle body:

Dirty Throttle Body

In addition, just for grins try banging on the bottom of your fuel tank with your fist or a rubber hammer next time the engine starts this flooding out problem. If the engine performance changes when you bang on the fuel tank, you might have a weak fuel pump.

Austin Davis

Posted in: Reader Questions

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