Help me determine if my 17 year old OE oil pressure gauge is failing
 

Please help me determine if my 17 year old OE oil pressure gauge is failing.

Recently ive been noticing from time to time my oil pressure gauge will jump. By this i mean that it will be steady just below the 60 mark then fall below the next mark (im guessing this is 30 or 40psi) and immediately jump right back to where it was and hold steady.

Even more recently ive noticed my oil pressure gauge will read just (maybe 1/4 - 1/2in) above 0psi. This has happened to me 2 or 3 times now. It happened to me this morning on the way back from class. It was reading good pressure on the way to school but on the way back it started reading low but not at first. I made it a few miles from campus and then while sitting still it noticed it was reading low. Each time im usually sitting still at a light. I dont notice any knocked in my engine when this happens and my oil levels are fine which makes me believe its the gauge or the sending unit. The sending unit is only 2 years old as i ordered a new one from mazda while doing my engine swap. However the sending unit is close to the y pipe (lsx swap) which does put off some decent heat but i doubt its hotter then the rotarys temps.

Any advice is greatly appreciated!

If i were you, before saying your guage is faulty I would check the oil level/pressure sensor first. Is it the same sensor as the stock or a different sensor you have for the LSX swap? But I believe you check the resistances in the sensor and see if it is out of spec or not. A weird sensor can do that and it's easier to replace that sensor than replacing the gauge itself.

-AzEKnightz

Your oil pressure sending unit is bad if the needle on the gauge "jumps" around or if it reads linear but is lower than normal. It's very unlikely the gauge went bad. Good luck.

Is there a resistance spec on the sending unit? or a way i can check the sending unit?

oil pressure
 

The oil pressure sending unit is one of the parts on a FD that commonly goes bad. Even if you replaced it, you still used the same Mazda replacement part that is apparently poorly designed. I have replaced the sending unit on my 93 FD twice in the last ten years. A sending unit on most American cars lasts forever. You might want to see if you can get a sending unit from Autometer, Kelsey Hayes or some other after market vendor and trash the Mazda one, especially since you have a bow tie engine in the car.

The stock sender is a POS. I had the exact same symptoms with a NEW sender. My gf's car has the same issue. I went thru the wiring, on my car, and still had a very intermittent issue... there was no pattern to it at all. Just to be sure, I hooked up an aftermarket one to my car and ran around with that for about a month... not once did the oil pressure do anything funny (as indicated on the aftermarket gauge). I'm going to remove the OEM gauge and run an aftermarket one from now on.

Im not going to purchase another sending unit as i can buy a nice gauge set for what that thing costs from mazda. Will an after market sending unit work with the stock gauge? If so which ones will work?

The 1994 Body Electrical Troubleshooting Manual (page C1-16) gives only a three-point calibration of gauge to sensor:

Gauge Reading (psig)............ Resistance to Chassis (ohms)

............ 0............................................. Infinite
.......... 60............................................... 28
........ 120............................................... 10

Thanks!!

Will any after market sending units work with the stock fd oil gauge?

my sender is bad too. 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.

I don't know of an aftermarket sender that works. New one from Mazda will do the trick and last for a good amount of time. They're about $80 or so new.

I put one in my car about 3-4 years ago and it's still doing fine.

Really, I would just put in a new sensor and call it done.

Dale

^Agreed.
The sender in my car is at least 8 years old. Occasionally I'll see abnormally low or irregular indicated pressure...usually at idle. Then I'll spend about 5 minutes cleaning the spade connection and all is good for another year or better.

my 300k sending unit FAIL

yeah, but that's 300k...

lol. it very much is