here's the deal... on my '91 Z28, 5.7, when the car is shut off the pump was still running for a few seconds, but not steady - it was intermittent, like it had a loose wire. i changed the relay, the amount of "run time" has decreased significantly and i haven't noticed if it was intermittent or not. i posted a thread on this in the electronics forum, and somebody there said that it is not supposed to run at all when the engine is shut down. a possible cause also would be the oil pressure switch sticking also. i have heard of this switch, but don't know where it's located. is it the same as the oil pressure sending unit? i have changed that one before, a couple of years ago, for spastic indications. so my questions are (1) is the pump supposed to shut down upon engine shut down, and (2) where is that oil pressure switch located? i have the same issue with my '90 IROC, as well, so i need to resolve this one day... the pump on the IROC runs for a long time, though - like 5 seconds... thanks...

KAM

 

That is fairly normal. As long as the engine has oil pressure above 4-7 PSIG, the pump will operate. Since the oil pressure must bleed off through bearings after the engine is shut off, it can take a few seconds, and even longer if the oil is cooler or more viscous. Mine does the same thing. As a matter of fact, all my vehicles do that, sometimes for 7-10 seconds in cooler weather.

If it really bothers you, you can remove the oil pan, install some worn out bearing shells (I can get you a set), and the oil pressure will bleed off faster after the engine shuts off so you don't have to listen to that nasty pump sound any more.

If the pump stops and starts again, that's a different issue. That could indicate a sticking/failing oil pressure switch, or an accumulation of sludge in the oil passage to the switch. Your's might be located near the distributor, right near and under the one for the oil pressure gauge. Since you have a later engine, it also might be mounted near the oil filter/cooler adapter. The switch you are looking for should have a large gauge orange and a large tan/white wire connected to it.

 

thanks, vader... no, it doesn't bother me at all, really. i was just trying to determine how it's supposed to operate. i was more concerned about the intermittent issue, so will try to locate the switch and see what i can find with it...

KAM