Have a fuel related problem with my 1990 camaro 3.1 v-6 auto trans car. Drove car to library last Monday. Came out and engine would start & run for about 4 seconds then die. Would repeat this behavior on repeated start attempts.
First thought was security system failure. But when key turned on security light cycles on then off like it should. Used scanner and security checks out with it also.
Ignition system is fine. Good spark. Pulled fuel rail, attached spare distributor which I hand turned with ignition on. All fuel injectors spray with a good spray pattern when dist is turned. Fuel pump also runs for key on prime and when dist is turned. Fuel pressure at key on prime is 43 psi.
Can run engine if I spray gas into throttle body. With scanner hooked up in data mode, all sensor readings are within normal limits except injector pulse width. Normal pulse wdith at idle usually runs about 1.7 to 1.9 . With engine not wanting to run unless gas sprayed into tb, pulse width is running at 1.1 to 1.2 .
Here's the crazy thing. Last Thursday, I came out started car and it ran normally, including inj pulse widths running in the normal 1.7 to 1.9 range at idle. Had not done anything to engine to account for this change. Engine ran and car drove fine.
Went out the next morning, started engine and it was back to dying after 4 seconds run time.
I've installed new spark plugs, swapped in known good iac, 2 other ecm, with no change. Checked power supply wires and ground wires and all is good. Engine still starts and runs for 4 seconds and dies.
I need some ideas on where to take my investigation next.
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