88
99,000miles
Stock
Oil level is good

Drove the car 2 hours and OP was fine. Get it home start cleaning the interior and attempted to take it for a ride around the neighborhood. I let it idle and warm up and when i pulled out the driveway the OP was normal, then after about 30 seconds of cruising at about 25mph, the oil pressure would touch 30psi then drop to 0.

I shut it off and pushed it home... (paranoid)

I'm thinking OMP.
What else could it be?

 

Factory specs are in the FSM, but they're approximately 30 psi at idle and 60 psi above 3k RPM. A severe leak from an oil cooler line / oil cooler itself can drop pressure, but that would be fairly obvious from the lake of oil on the ground. The OMP/MOP does not operate under any real pressure, so that's not the problem. The oil "injectors" just drip oil with the assistance of intake air pushing it in. Don't confuse the metering oil pump with the oil pump.

A front cover o-ring failure can drop pressure as well, and that would mean removing the front cover and everything attached/in the way to get at it. Not fun.

It could also just be the oil pressure sender, or oil pressure gauge reading incorrectly. Check the wire to the sender. It is located under the oil filter, and will look mushroom-like. The wire clips onto it. Clean the contacts and reattach it. Start the car and see what the oil pressure looks like at idle and above 3k RPM. There is also a test for the gauge in the FSM, but you will have to buy a few resistors to check it.

 

FDs have similar issues with an open spade connector at the sender. It's proximity to the oil filter pedestal means it can get dirty. When that happens, indicated oil pressure is affected, usually at idle, since that's when the signal is weakest.
Most rotarys have at least some dilution of oil with fuel over time. If it's been a while since the last oil change, especially with a low viscosity oil, that can affect indicated pressure as well.
Clean as suggested above. A little sand-paper and contact cleaner. If the levels are good and it's still giving weird readings, consider a new sender.

 

No oil appears to be leaking from the front cover,
And HAHA no oil lake.

Cleaned the contact and started it.
The oil pressure rises to 30psi and then falls to ~15psi? and doesn't move from there even at 3k rpm.

After about 30 seconds it fell to right above 0.
No Change...
Bad Oil Pressure Sender?

Also, this is irrelevant but, my previous NA S4 RX7's both have had what appears to be a ground disconnected. It is in the area in between the oil filter and brake booster. What is it there for?

 

It's a condenser. There's one for the oil pressure gauge and one for the ignition system. The one for the oil gauge is Yellow/Red. If it's disconnected you might want to reconnect it. There's a debate, I'm sure, whether it would have an affect or not regarding your problem.

 

The "condenser" connected to the Oil Pressure Sender? That is what i disconnected to clean.

This is what I was curious about.

 

There's a single wire connector going to the oil sending unit. Did you clean the condenser thinking you were cleaning the connector to the sender? If that's the case, the sending unit is a mushroom shaped unit screwed into the side of the engine housing at a point below the oil pedestal. The wire is Yellow/Red and the connector slides off as opposed to being pulled off if that makes any sense.

 

Yes the single (yellow/red)wire that slides onto the end of the oil sending unit was what i cleaned off along with the part it slides onto.

 

Where can i attach that tab, Its supposed to go under the slave cylinder correct?

 

Any decent grounding source would suffice.

 

Got it grounded and still no change in oil pressure.

It rises fine on startup, but falls back to 0.

 

Oil pressure can be confirmed with a mechanical gauge. I think some auto parts stores may even rent the proper gauge setup.

This is the testing procedure for the oil pressure gauge. If you get 3 resistors with the proper resistance values, you can temporarily connect them to the wire that normally connects to the sender. Ground this wire/resistor and you should get the indicated value on the gauge. This is from the body electrical section of the FSM.

 

I experienced the same issue with my FB before the rebuild. There's an O-Ring that goes between the front cover and the the passage from the front oil pressure regulator, when it fails it gives these symptoms.

 

check your sender for sure. my car has no leaks, fresh oil, reads linear at about 1/3 too low at all times. meaning 60mph = 35 or 40 psi and idle = 5 psi. but it moves up and down with RPM's as it should.

sender in the FC sucks.

 

my 300k sending unit FAIL

 

I ordered a sender (should be in today)
Mine reads on startup but drops to 0 and hardly moves from there, 1/8th of an inch if any movement at all.

 

awesome. when you replace it - let us know how difficult it was. if it's not hard, i might replace mine too.

 

Not hard at all the only thing i removed was the trailing plug wire

Its fixed now...
BUT now my voltmeter stopped working.

 

awesome. i'll look in the FSM for mine and fix it up too.

did you get at it from under the car or above?

 

above

really only took 10 minutes (ratchet wrenches)
and about 5 minutes of that was me to cleaning the area up.