Starter issues

[Schurkey]

That's odd, there is a start relay to energize the fuel pump on start. Typically it runs for 2 seconds when you turn the key one

Yes. Except it's not a "start relay", it's a "fuel pump relay".

then once oil pressure comes up the oil pressure switch energizes the fuel pump.

Not exactly right. The ECM powers the fuel pump relay for two seconds when the key is first turned "on". Then the ECM shuts-off the fuel pump relay UNLESS it gets a "crankshaft is turning" signal. If the ECM gets a crankshaft-is-turning signal, it turns on the fuel pump relay as long as the signal is present. This is the PRIMARY way the fuel pump is energized. The oil pressure switch powers the fuel pump as a back-up/redundant feature should the ECM, the fuel pump relay, or the relay wiring harness fail.

Usually a long crank happens when the relay fails and the engine does not get fuel until the oil pressure exceeds 4-6 psi.

True.

If the pressure senor died it would crank and seem to catch then die.

Not if the primary system--ECM, fuel pump relay, and wire harness--was working properly.

If both the primary and secondary (oil pressure switch and harness) systems are working properly, the current draw of the fuel pump is split between the relay and the oil pressure switch based on Ohms Law. If either system fails, the other supplies all the current needed.

SO: If you fix the oil pressure switch, and the fuel pump works better, you still need to fix the fuel pump relay/harness/ECM problem, because if that worked properly, you'd never know that the oil pressure switch system had failed.

[padgett]

Except if the engine looses oil pressure the oil pressure switch is supposed to turn off the fuel pump even and especially if the engine is running, at least that was the original design back in the 70s. I have seen it documented both ways.

ps ok on "fuel pump relay", again I have seen both.

pps guess the only way to be sure is to instrument and shut the oil pressure switch off.

ppps some of my terminology is from when I worked for GM and may have varied between divisions. We are in agreement on most of its purpose.

[Schurkey]

Except if the engine looses oil pressure the oil pressure switch is supposed to turn off the fuel pump even and especially if the engine is running, at least that was the original design back in the 70s. I have seen it documented both ways.

ps ok on "fuel pump relay", again I have seen both.

Look at the wiring diagram. The oil pressure switch can cause the pump to run if the other system fails. It can NOT turn the fuel pump off UNLESS the other system has failed. The fuel pump can run equally well through the relay and it's harness, or the oil pressure switch and it's harness. They BOTH have to open to shut the pump off--assuming they both work to begin with. I can't vouch for what was done on other carlines, or by hot-rodders removing an engine-driven fuel pump in favor of an add-on electric. I'm talking about first-gen W-bodies. (and also my '88 K1500) It seems to me that fuel pump relay/oil pressure switch was kind of "GM Standard Engineering Practice" at that time.

pps guess the only way to be sure is to instrument and shut the oil pressure switch off.

Or pull the wires off the oil pressure switch and see if the engine immediately dies.

[project 92z]

Today I had a remote starter installed and the small illogical part of me hoped that this issue would be bypassed and go away. No such luck. In fact the problem seems worse now because I have to wait for the remote system to reset. Honestly I don't remember if I ever tried the relay or could find one labeled starter but the other possibilities were covered. I'm just hoping someone would see this bump and remember something new.