98 Tahoe runs 1 second, goes dead

Could this be the oil sending unit ? Decided to replace it but it’s a bear to get to. Then I read on here that the oil sending unit has bypass circuitry that no longer kills the fuel pump if oil pressure drops too low, as in some earlier GM models. It has an Excalibur alarm system on it, but it seems if this was the problem it wouldn’t crank to begin with. Any ideas ?

Welcome Aboard!

If you suspect a fuel pressure problem, jumper the FP relay so it runs constantly, then start the engine. There is little sense in digging into the oil pressure switch and wiring if the diagnosis doesn't point you in that direction.

I misread the post and pointed to a starter issue, Blue Bowtie is on point.

Run 1 second and die sounds to me like the security system- not reading Passlock II resistance properly. What is security light doing? It should come on then go out after start.

BR is getting ahead of me. I was trying to get you to eliminate one item at a time.

Of course, he's correct as well. The security system will run the injectors for only about 2-3 seconds if the key transponder doesn't read. I just wanted to see if the fuel pump ran or not, taking us another step down the diagnostic path in one direction or another.

Incidentally, the auxiliary oil pressure switch does not act as a fuel pump cutoff, and it never did on domestic GM vehicles - All the way back to the 1976 Cadillacs. I believe Ford tried that for a while. It was one of their "better ideas."

Just as a side note, my 1977 Vega had the FP wired through the oil pressure switch OEM- Never had to check the oil, the 270 degree exit ramp would tell me if I was low. Engine would cut out on long curve- If I straightened up, it would cut back in again. Oil light would come on at same time.....

Vega? I'd almost forgotten about them. I guess that counted as a GM vehicle, and they did have some unique features. Good education.