ok , so im trying to get the oil pressure gauge in my gf's 85 12 gs working. since its never worked i started by checking to see if the wire going to the sending unit had fire on it when the switch is on and it does. i then found another sending unit (i got it in a pile of parts so i dont know if its any good or not) and switched them out started the car and it still didnt move, but i noticed when i revved it up although still staying on 0 the needle did move just a hair. so im thinking that the second unit is bad too, but before i go on the hunt for another one does anyone know what range the sending unit should read on an ohms meter at idle and revving up? thanks

 

Take the wire and ground it... The gauge should peg. If it don't you got a wiring problem or a gauge problem..

 

that wont mess the gauge up or short anything out by grounding the hot wire to the body or neg. post on the battery?

 

Grounding it will simply put the max voltage to the gauge - and that's the way it's supposed to work. You won't break it.

 

ok, so i did the test above and found that the needle goes all the way over past 110, so going by this info i just need a good working sending unit that screws into the engine. if anyone has an extra nice working one please let me know, thanks

 

ok so i got another sending unit and put it in the motor hooked it up and got in the car when i started the car the oil pressure gauge went up about 30 as it was building psi then stopped and went back to 0 and hasnt moved since. surely i couldnt have 3 bad sensors any idea what could be wrong im getting fire to the wire and when i ground it the gauge pegs out to the other side, so im lost. thanks for any help.

 

just get a mechanical gauge and the adapter that goes under the oil filter like i got and be done with it.

 

The mechanical gauge is a good idea. The stock gauge is nice for the stock look but (as you're finding) can be hokey.

If you REALLY want to keep that stock look:

Go ahead and try pegging the gauge again by hand.

Then check yoursending unit as outlined in the FSM.

If the gauge & sender are working, you may have fouled wiring or a break in a wire. A broken wire that is intermittent is a real bitch to find and, in my experience, just ain't worth it. If the wiring is the problem or if you're game for the troubleshooting, get some same gauge wire and run that, piggybacking it to the harness. Then connect it to the gauge. Then see if it works.

But, as was said by Rxtasy3 - mechanical gauge.

 

well since this is my gf's car and not mine as for now adding an extra gauge is a no go for now, we want to keep the intierior all stock. thanks for the referance to the fsm i'll get a tester from work tomorrow and check the risistance and post what i find.

 

I hear ya. Still, you can add a gauge pretty easily without drilling holes in anything. If you have to go that route, just sharpen a coathanger. ;-)

 

Hey project7s here are a few pics from a post I had up in the What did you do to your FB today? in the non-technical section.









I didn't need the oil temp sensor anymore, and the oil pressure gauge for me was pointless since the original one works just fine for me. So I took those out and went with the water temp only because it's the only one I really cared about.

I screwed that holder on the bottom facing screw of the little carpet piece.

It's relatively easy to install, and you could do the pressure gauge where I put my water temp gauge for relatively cheap and a day's work. Here's a list of parts you'd need:
-Oil filter sandwich with 1/8NPT ports eBay cheap adapter for reference
-Gauge install kit 1/8NPT Autometer pressure install kit
-Mechanical oil pressure gauge Auto Meter Ultra Light Pro Comp mechanical oil pressure gauge
-Gauge carrier Actually, this is the one I used

And just install those and you're all set!

 

ok, so i tested the gauge with a omhs meter like the fsm said to except instead of it reading numbers like it said it would it just went to ooo.o, so i tested it on my se which i know works and came up with the same reading so i just said ah screw it it aint this important, BUT tonight i got in it to go eat and noticed that when you turn the switch on the needle goes over and pegs 110 then when you start the car it goes back to 0. my first thought is the sending unit is for a car with an idiot light instead of a gauge, cause they will light up with the switch on and go off when started. i'm thinking if i get a new one from like mazdatrix it should work, right?

 

I'd sure as sh*t hope it works! Let us know if that fixes the issue, I'll look at the wiring FSM and see if there's anything there..

 

Erm. Well, you should test the sending unit, too. Couldn't find it in my FSM or my Chilton (78-89), but rule of thumb is that there shouldn't be a difference of greater or less than 500 ohms on an oil pressure sending unit between engine off and 'warmed up'. Someone please correct me if this unit is different, I haven't tested one lately.

Make sure that the connectors are clean. They can get gunked, have oxidation, or both.

You've already tested the gauge, so we know that's good. Or we hope so.

If you've got clean contacts, good resistance differential between warm and cold, the problem has to be the wiring/gauge.

If it's bad, it's bad. But before you stick a new one in, check the last time you changed your oil. ;-)

 

well i changed the oil about 3 weeks ago, and the sending unit in it now is not the original one plus i sprayed it out with break cleaner before i put it in. the reason im thinking its not a wire is as soon as you ground it to the body it pegs 110 instally evertime, and everywhere i look nothing says anything about what kind of reading the unit its self should be.

 

that's not uncommon, the connectors usually are dirty and corroded after all the years. you can always snip it off and crimp on a new female spade connector which will slide right onto the sender with a little force.

i don't necessarily like brand new connectors standing out in the engine bay but whatchagonnado.

 

im pretty sure that its making a good connection be cause if you remove the wire from the sender and turn the switch on it doesnt move at all, then hook it up and it pegs 110, then start the car it goes back to 0. it like its working as if it were i dummy light and not a gauge.

 

Did you ever figure this out? I have a similar issue with my oil pressure gauge pegging out past 110 psi once the car starts up.

 

I was hoping someone had the answer to this I have the same problem