i have a 1987 iroc z with a 350. i have a problem with my oil pressure. when i drive my car for like 10 miles my pressure will be fine but after about 10 miles of driving when i would stop at a light my oil pressure would drop to zero and my idle is off like my car wants to die. When i step on the gas just a little at the light my pressure would go up and be fine, but when just on the brake my pressure goes to zero and hard idle, so im stuck and not knowing what it could be causeing my low oil pressure and bad idle.

 

try a thicker oil if that solves the problem then the bearings are worn out it could also be the pickup tube fell out of the pump or the pump going bad. when you do a oil change look through the drain plug hole and see if everything looks okay if you have metal shavings in the oil its going to be time for a rebuild

 

Are you talking about what the gauge shows, or the actual oil pressure?

 

Simple thing to look at is the oil level. Your oil filter might have some trash in it causing blockage. Don't know how old or how many miles are on your engine but the bearings could be shot and in turn would require an overhaul. Also if you change the oil. Cut your old oil filter open and look at the filter media for any metal. This could a strong indication of bearings going bad.

 

I am not saying this is the problem, but it was when mine started showing similar symptoms last march.

It could be the oil pressure sensor. The gauge showed good pressure until I drove it a while and then it would drop. The computer will try to make compensations when it gets bad info from various sensors. A bad oil pressure sensor can cut the car off completely when it shows pressure sinks below a certain level. I changed the sensor out and did not have that problem from that since.

 

That's the most common caust of "bad oil pressure".

The computer knows nothing about oil pressure, and low oil pressure can only cut the car off if the fuel pump relay fails.

 

Wow! I love this forum! I didn't know that the op sensor was linked to the fuel pump relay. Thanks for sharing that. I thought it strictly had to do with the oil pressure going below a certain level (thinking it is 4lbs).

So my reasoning was yes, the computer does take into consideration the pressure as perhaps a safety feature to keep a guy from burning his motor up. I thought about asking you Apeiron why and how they were linked and what the fp relay and op sensor had to do with each other, but thought I would search online first and what I found was a debate going on another forum on a chevy truck. Granted there is a slew of differences in how specific vehicles are designed and function on the detail levels, but was wondering if I got the jest of how things work there.

Those circuits both go to the ecm - the run "parrallel." The oil pressure becomes a factor to the ecm when the op sensor ( a variable resistor run by pressure) closes. So it seems like the ecm monitors the oil pressure and will shut the engine down when the pressure is low enough. This is the case only if the fp relay is not functioning? Because it serves as a back up to the fuel pressure relay as well.

Anyway, this is the link:

http://www.automotiveforums.com/t966...l_cutoff_.html

Most of what they were saying was way over my head. It started coming a little more clear when "ronaldk" came in on the post.

However, one thing that I am thinking over in my mind because I used to work at a relay manufacturer. There are so many ways for a relay to go bad, and some of those instances they won't show up in every test. Solder bridges, small cracks in the board, and other factors can cause the relay to perform differently under various operating temps. In heat, a crack or bridge can cause it to swell out of making a connection. When things cool, they can shrink back into place. Or it can be vice versa.

So the only time the computer cares about oil pressure is when it goes below 4lbs (or whatever that critical low point is) only when the fuel pressure relay does not work?

 

No, the computer doesn't care about oil pressure ever. There is no connection from the oil pressure gauge sender to the computer.

 

I see now. It isn't that the oil pressure sensor is connected to the ecm, it is just that it sort of serves as a back up when the fuel pump relay goes out. If the op sensor goes out too, I've got no fuel so that is what cuts off the motor; lack of fuel.