Okay, my brother-in-law asked me to come look at and scan his truck today (1992 Chevrolet 5.7-liter TBI). It WAS giving codes 12 and 15 (15 - coolant temp sensor) and he THOUGHT a 21 (throttle position sensor) - turns out the 21 was a hallucination. NOW, it flashes 12 good and solid twice, then gives a quick, weak 1 and a strong 2 for a code 12, then gives a 5, long pause, 4, long pause, 3, then nothing. And if you turn off the key, then turn it back on, it doesn't give any codes at all. This can't be right - I know that valid codes have two digits.

Under the hood, with the engine running, when the CHECK ENGINE LIGHT starts to flash on and off, you can watch the injectors start dumping fuel, then trimming it back. Naturally, when it does this, the idle speed comes up and the exhaust gets black. This problem appears after the engine has warmed up for a considerable time. We swapped the broken temp sensor for one out of an '88 Chevy 1/2-ton with the 5.0-liter TBI, and it didn't really change anything. Unfortunately, my scan tool won't log data on this engine - don't have the TBI cable.

A little history on the vehicle - after it first started exhibiting symptoms, and I suspected fuel supply as the problem, the owner changed the fuel filter, and it was WAY past time. During the diagnostic process, however, I noticed that the engine had been started with the jumper stuck in the ALDL. I remember reading that this is not good for the ECM. Later, after the filter swap and during a test drive, I'm told the engine quit twice and that a fuse replacement both times allowed it to limp home. It was first thought that the fuse was the fuel pump fuse, but it turned out to be the ECM fuse. Is my brother-in-law looking at replacing the ECM on this truck? That's what it's beginning to sound like to me. Any input is greatly appreciated. Thanks - Chris