ok, here is my problem.
my 91 z (305 tpi) just had the intake resealed. there had been coolant in the oil and vise versa. i am 99.999% sure that this was b/c of the intake, bc the car was fine before. now since i got it back, it wont hold an idle when you first start it, unless you rev it a little. once you drive it for a few seconds it holds it idle fine (about a couple hundred feet of driving), but still idles a little funny-but barely noticeable.
also, the oil press. gauge reads about 45 psi at cold startup, then as the car warms up, it drops to about 30 while you are driving, and when you come to a stop, and the car is idling in D, the pressure gauge drops to zero

any help would be greatly appreciated, thanks

 

 

since the battery was unhooked for a long time when you had the intake resealed, the computer has to relearn idle. sometimes it can take a day or two. some people dont have a problem with it though. my iroc ran terrible for a day when i changed the computer. oil pressure problem seems normal when you said it was cold and hot, but when idling, it seems funny. if the engine had zero oil pressure, the engine will not run cause the fuel pump runs off an oil pressure switch on the engine. so you got to have some oil pressure at idle in D or the engine wont stay running. i would check your oil pressure with manual gauge to compare it with the indash gauge.

 

Incorrect, the fuel pump relay keeps the pump running, not that pressure switch. That switch is for when the relay fails and will run the pump for emergancy use. This will be noticed by the longer crank times because the engine must build oil pressure before the pump will run.

 

if your oil pressure is dropping to zero, id be worried your bearing clearances are too big. might be rebuild time.

 

the relay is for priming the fuel system. when you turn on the key before you start the engine, you will hear a click(relay) and the fuel pump run for 2 or 3 seconds. this is to get the engine started and when its gets oil pressure, the oil pressure switch takes over suppling the fuel pump with voltage to run the pump. if the switch fails or if the engine has zero oil pressure, the engine wont run. it will still start up cause of the relay priming the fuel system but die right after it starts.

 

That is incorrect. The oil pressure switch is the backup if the fuel pump relay fails. You want proof? Start up your car. Disconnect the oil pressure switch. Gee, the engine keeps running, doesnt it?

Of course it will not stay running if the FP relay is bad.

John is correct.

 

i am in the process of rebuildin my 305. my intake was leakin too. i had no antifreeze in my oil but it was still enough to contaminate my rod and main bearings. if your leak was severe enough to see coolant in the oil, your bearings may be on their way out. mine were severly contaminated from just a small leak. rod and main bearings dont like antifreeze

 

ok, the running problem is gone at startup, it starts fine with no pumping of the gas.
but the oil pressure problem does worry me. one of the problems it could be is the oil pan has a dent in the underside.
but i dont know if i should replace the pan, or start saving for building a new engine.
when its warm, and at idle, the oil pressure is at zero, but i doesn't make any noise, or die
hopefully ill get this figured out

 

If your oil pressure really dropped to zero, I cannot believe your lifters would stay pumped up and your rockers would begin to make a very loud racket. I'd try the mechanical oil gauge to see for sure.