1987 Pontiac 6000 4cyl quits, works fine after 30min w/ hood open?

Question

So I've got a 1987 Pontiac 6000 with the 2.5L 4cylinder engine and TBI. It has been sitting for a few months, so I would expect some occasional hesitation due to the old gas, and have added a bottle of Techron to help clean out the fuel system a bit. Mostly it runs quite well though.

Unfortunately, my real problem is that after driving the car for 10 minutes or so, it likes to quit running, usually in the least appropriate spot (right turn lane, merge lane, etc.) And it won't start up again until I leave the hood open for 30min or so.

The fuel pump relay may be marginal since the previous owner (a mechanic) rerouted some coolant lines and they are pressing against it, but when it doesn't run I can look and see fuel coming out of the injector when it cranks so I don't think that's the main problem.

So where would YOU start looking to diagnose this?

Thanks,
David

Answer 1

I'd think sensor problem. O2 sensor?

Since it runs OK, but dies AFTER it has warmed up and at idle speeds, you can rule out fuel system, and ignition system.

After the engine warms up to operating temperature, the computer goes into "closed loop". Meaning the air/fuel mixture is controlled by the sensors. If one sensor is malfunctioning, it will give the computer false readings.

Just for fun, disconnect the wire to the oxygen sensor next time it dies.