so i was searching around other threads that have similar issues, but i have yet to find one like mine

on friday, i took my car to the local mechanic to have the oil pan redone because it was leaking oil and an oil change while it was there. i decided to go with 10w-40 since it's been a bit colder from 20w-50. after a bit, the shop manager came out and told me the oil pressure sensor was leaking so they had that replaced and the old mount that bolted to the oil pan.

let me say my car ran normal, had 20-30 oil pressure at idle and around 50-60psi at 3k rpm. after i got the car back, it was fairly normal but yesterday while driving to my dads house, i noticed the oil pressure gauge was sitting at less than half between 0 and 30psi and when i jumped on the freeway, it barely reached 30psi at 3k. the car also stumbles when coming to a stop, the RPMs drop then come back up.

i plan on taking the car back after class monday morning, but i was hoping someone someone could answer a few questions.

1. can lower viscosity oil cause this much of a change in pressure?

2. why would the old leaking oil pressure sensor give good readings while the "new" one give worse? shouldn't it be the other way around?

3. i cleaned the clip that attaches to the oil pressure sensor and i noticed it protrude a bit further out than the old one. i can still see the threads on it. does anyone think this can cause faulty readings?

just a bit more info on my car, 1986 GXL automatic, 84k miles, recently took off the UIM, replaced a good majority of the vacuum/coolant/fuel hoses.

 

1) Yes.

2) No.

3) Possibly.

 

That's not the oil pressure sensor. That's the oil level sensor. Double check the oil level, as that can affect the readings like you are describing.

 

wait, i thought the oil pressure sensor was mushroom shaped right under the oil filter? that's what was replaced. the oil level is fine even when i check it a few hours ago.

 

the wire for this sender is spliced just a bit further down
and tees to a connector that clips onto a small black square condensor that is bolted to the firewall adjacent or to the clutch slave on some manuals
this is a dampening circuit , and unclipped can make the sender erratic

 

You are correct. I think I mis-understood your description of the work done.

 

Well, it starts up fine going to 60psi on cold start up. After warmed, a smidge below halfways between 0 and 30psi. It still fluctuates when I accelerate. Class is about to end so Im about to leave...i hope its nothing too serious *crosses fingers*

 

Last thing to do will be to pull the front cover and check on the front cover o-ring. When it is warmed up, and you increase the revs, does the oil pressure increase as well?

 

The stock gauge is extremely unreliable, please attach an oil pressure/line pressure gauge to the pressure sensor port and record readings before doing anything.

And lower viscosity oil will not cause a massive difference in pressure.

 

I would never trust the stock oil pressure gauge.
Get a oil pressure test gauge and hook it up to the stock pressure sensor location. Mines has a pretty long hose which I can route it through the hood near the firewall so I can see the pressure while driving temporary.

I would just get an aftermarket gauge and sensor.

My stock gauge and sensor says at 3k rpm I am at 40psi, and at idle its basically at 0....
With an aftermarket gauge and sensor, even the test gauge, it shows at 3krpm I was at 80psi (FD regulator) and at idle 24psi.

If you do check the front cover o-ring, remember to hold the clutch in the entire time of the removal!!!!

 

when warmed, the pressure still increases when i rev. it still runs normal, except for the funky idle when coming to a stop.

thanks for the inputs so far as well

 

I am having the same problems as you are having my oil pressure is almost non-existant and the idle is off when stopping o was just wondering if you ever found out what your problem was?

 

As stated, verify pressure with a decent gauge. The stumbling RPMs are more than likely due to your TPS sensor being out of whack. Simply adjust it and it should be fine. Here is a link on how to do it if you don't know.

2nd Gen TPS Adjustment

 

The most obvious that comes to mind...

Check that the "ground" that connects near the slave cyl. that falls off during maintenance is there... Nearly every RX-7 I've owned was missing, dirty, or relocated to a poor spot.

Taken from Aaron Cake...

There is a semi-ground that can usually be found on the slave cylinder mounting bolt closest to the drivers side. This is a capacitor to filter the signal to the oil pressure gauge. It connects to a single spade style connector on the yellow/red wire found on the engine harness. While not super critical, strange behavior on the oil pressure gauge can result if it is disconnected. These like to disappear after a transmission or clutch job so don't be surprised if yours is gone. This ground is serviced as described above. Clean the contacts, cover with dielectric grease on both ends and reinstall with clean hardware.