balky oil pressure reading in 94 FD
 

So, it's been a long standing issue that these FD OP gauges are prone to being totally bogus. I see from searching that a lot of people say 'clean the conductor contacts at the sensor' or 'get a new sensor' fixes it. Well, I've done both, AND installed a secondary oil pressure gauge (which reads much higher than the dash cluster oil gauge all the time), so now I want to tackle whatever the issue is with this OP instrument. I recall some time ago, there was a 'fix' similar to the 'linearizing of the water temp gauge' discussed. Is there an archive on 'fixing the oil pressure FD gauge', and if so where can I find it?

See my post at the end of your other thread...

I have a '94, my oil pressure was flaky when I got the car back in '04. Bought a new sender and have been good to go. Only recently it started reading a little low, pulled the sender, cleaned out the passage going into the sender with brake clean, good readings again.

What exactly are your readings?

Also the oil pressure gauge really isn't that important on a rotary. Mazda designed an awesome oil pump that makes good pressure even if it ate half a bearing through it. I just like having a gauge that doesn't look broken.

That said I also see zero reason for an aftermarket gauge.

Dale

DId you test whether the other oil pressure gauge is accurate?

Yes, the secondary sender is mounted on a T that the EOM sensor is also mounted on now. The OEM sender reads 0 when I'm at idle, while my secondary sender is around 10 psi or so, and it goes up to 60/70 while driving. The OEM gauges reads maybe 15-30 at most. Wildly off. I also have another gauge that I have checked this with, it's the OEM unit. I will remove it again, clean it out, and the terminals and see if that makes any difference.
A long time ago, someone used a flex pipe to the block and remote mounted the sender on the body.....He said it was both a vibration and a grounding issue.....

Interesting... I wonder if there is an issue with the OE gauge in the dash... The odo and tach fail occasionally. Why not the other gauges too...

Here's an excerpt from the FSM/Body Electric Manual that covers testing to isolate problems with the pressure sender from the OEM gauge in the dash. The gist of it is you substitute the SST (which is apparently just a resistance substitution box) for the pressure sender in the circuit, and check that the gauge reads where it should for the resistance values shown.

https://cimg5.ibsrv.net/gimg/www.rx7...ee6cb4af19.png

subbing as i think my sender will likely need cleaned as well for starters

A healthy FD should be about 30psi at idle, 60 or a bit more at 3000 RPM.

It's EXTREMELY hard to have low oil pressure. The biggest cause I've seen (that I have done myself) is a bad, torn, or missing O-ring between the front cover and the front iron. In general, it's good to verify oil pressure on a new engine and once the break-in and debugging process is over there's not much that would cause any substantial oil pressure drop.

With some resistors or a variable knob-type resistor you can duplicate the Mazda SST to test the OEM gauge.

Dale

Well, learned about a new tool thingy today :)
​​​​​​​Hopefully, I'll never need to learn how to use one.

Resistance substitution boxes/circuits come in super handy for troubleshooting various automotive problems like gauges. Here's the one I've been using for many years - still cheap, but looks like Amazon doubled the price since I got mine!

This has been a reoccurring problem with my 92 FD. The first time I installed a new pressure sending unit. Then after a few years, it had the same problem.
That time I crimped the female spade connector so it had a tighter fit. This worked for a while.
Since then when the problem occurs again, I just remove the sending unit and clean it out by spraying WD-40 into it and slinging it out.
The oil that goes inside the unit stays there and after a while it must deteriorate and causes some gumming or something.