1989 IROCZ TPI 350 Oil gauge is reading good when cold after warming up the pressure goes way down. I put in the oil pressure send unit and didn't work. Is there a senor under the hood and if there is where is it? Please help.:confused:

The oil sending unit is on top of the block, at the rear, drvr side, under the distributor.

If you have low oil pressure, you should have gotten a "Check Engine" light.
For troubleshooting purposes, sub in a mechanical pressure gauge, indicating from 0-100 PSI. Normal hot oil pressure at idle I would expect would be 20 PSI.

Ev, I thought the engine won't run without it... I thought fuel pump latched via OP sender? Or am I fubard again?

That's a 2 or 3 wire sensor on a 86(Idunno on 89)305, huge compared to older senders. I have one somewhere:). Not fun to r&r on this model.

pretty sure there are 2 sensors, 1 for the guage, one for the ECM?
Also not all cars have a low oil pressure shutdown, those that do have a switch type sender wired into the fuel pump circuit. Not sure if this one has that.

what are your gauge readings, hot and cold idle, and hot @ 2000 rpm?

It's pretty normal for hot idle to be considerable lower thatn cold idle.

Parallel path, one is ECM controlled f/p relay, the other is thru o/p sending unit bypassing the relay.

So what you are saying if I replaced the oil pressure sending unit and didn't fix the problem then the problem is the F/P relay switch. No "Check Engine" light but my son said the car stalled already two to three because of this oil pressure being low, I think
Hot idle is almost all the way to 5 or lower and cold idle is 25 or better.


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sounds like it might be time for engine repair if the oil pressure is that low

or as a bandaid you could try thinker oil, say 20w-50
I am doing it right now to put off a rebuild until I can better afford it

Possible oil pump installation? I'll clean the F/P relay switch connections and then I'll put in 20-50w oil. I don't think the oil sending unit is on top of the block, at the rear, drvr side, under the distributor. I installed a new oil sending unit and it's on the side of the car engine drivers side. Correct?

You probably are correct. I'd pour in a can of STP Oil Treatment.
Fuel pump switch at the dist, two wires, maybe four?

I looked behind the dististributor, nothing on the block. The one I replaced was in lower block on the left lower side, it's black plastic. 3 inches long and screw in the block and has wire that plugs in. I did try a can STP oil treatment pressure a little better and will also pour in 20-50W oil. The question is does it need an oil pump or rings or something else?

Reads like you'll need a crankshaft kit, comes with a ground undersize crankshaft & fitted oversize bearings. Complement the kit with a new oil pump.

But then you're this far, either a short block rebuild the heads, or buy a long block (short block with heads and a camshaft & lifters, no sheet metal, to finish it off and do it correctly.

I looked behind the dististributor, nothing on the block. The one I replaced was in lower block on the left lower side, it's black plastic. 3 inches long and screw in the block and has wire that plugs in. I did try a can STP oil treatment pressure a little better and will also pour in 20-50W oil. The question is does it need an oil pump or rings or something else?
I think my 92 is the same place, just above the oil filter, nothing at the dist. If I was doing a rebuild I'd put new cam bearings too!

Jeff