Oil Pressure Gauge (Page 1/2)
Rhodesia1977 JUN 01, 03:38 PM
I have tried to search the forum for this answer but for some reason, nothing will come up. I am probably not doing something correctly. Here is my question:
I have a 1986 GT with about 93,000 miles on the odemeter. Last year the oil pressure gauge would work fine until the car warmed up after about 10 minutes of driving then the gauge would stay pegged all the way to the right. The next day, it would do the same thing, work for a while until the engine warmed up. I checked oil pressure with a pressure kit so I know I have good pressure and my oil level is always spot on. I checked and cleaned all grounds and wires. Now lately, as soon as I start the ignition, the gauge pegs all the way to the right and stays. When ignition is turned off it goes back to zero. Any ideas? New oil sensor maybe? Any help would be appreciated. Thanks for your time!
hunter29 JUN 01, 03:49 PM
Upgrade to the 88 sender, see cave, then go from there, you likely need it anyway.
Rhodesia1977 JUN 01, 04:16 PM

quote
Originally posted by hunter29:

Upgrade to the 88 sender, see cave, then go from there, you likely need it anyway.



I will check that out. Thanks for answering!
theogre JUN 01, 04:50 PM
OP sender or wire(s) to it are bad and cause same as you unplugged the sender.

First get engine hot that causes this... Unplug sender. Check for ∞ Ω between OP pin and engine block.
Likely Can turn off engine but turn on key right after shutdown to keep gauge hot for other test later.

See cave page above for which pin to test. (Because Both Fuel Pump pins should read ∞ Ω to the engine.)

If it have 0 to 90Ω then likely not sender but wiring problem and can have worse problem or fires depending what other wires are bad.

Could be the gauge is hot and get bad connection...

Check by unplug the sender. ground pin in the in the plug w/ small wire. Should instant drop to 0 pressure on the gauge.
No?
Then pull gauge pod leave wires connected and short ground (black) to OP (tan). (pink/black is "12v" thru gauge fuse.)
If that drops then have wiring problem.

If have an old sender... then have old plug and they go crap and won't work right at best.
Upgrading to 88 sender solves several issues at same time but may or not fix you gauge pegging problem.
One issue if 88 sender dies won't leak oil 99% of fails like old senders often do just that and empty the oil pan. Worse, Old senders can work perfect and leak till oil pan empties then finally read 0 psi and can "burn" the engine w/ no oil fast.

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

Rhodesia1977 JUN 01, 05:02 PM

quote
Originally posted by theogre:

OP sender or wire(s) to it are bad and cause same as you unplugged the sender.

First get engine hot that causes this... Unplug sender. Check for ∞ Ω between OP pin and engine block.
Likely Can turn off engine but turn on key right after shutdown to keep gauge hot for other test later.

See cave page above for which pin to test. (Because Both Fuel Pump pins should read ∞ Ω to the engine.)

If it have 0 to 90Ω then likely not sender but wiring problem and can have worse problem or fires depending what other wires are bad.

Could be the gauge is hot and get bad connection...

Check by unplug the sender. ground pin in the in the plug w/ small wire. Should instant drop to 0 pressure on the gauge.
No?
Then pull gauge pod leave wires connected and short ground (black) to OP (tan). (pink/black is "12v" thru gauge fuse.)
If that drops then have wiring problem.

If have an old sender... then have old plug and they go crap and won't work right at best.
Upgrading to 88 sender solves several issues at same time but may or not fix you gauge pegging problem.
One issue if 88 sender dies won't leak oil 99% of fails like old senders often do just that and empty the oil pan. Worse, Old senders can work perfect and leak till oil pan empties then finally read 0 psi and can "burn" the engine w/ no oil fast.




Thanks for the tips!
greenturnedblue JUN 01, 08:09 PM
If its the original sender its probably toast by now. This was mine that I replaced two weeks ago, it was causing similar issues
Rhodesia1977 JUN 02, 06:38 AM

quote
Originally posted by greenturnedblue:

If its the original sender its probably toast by now. This was mine that I replaced two weeks ago, it was causing similar issues



Thanks for the reply and pic. I am trying to figure out how to remove that sender. There is nothing in my Haynes repair book about it. Was it difficult to remove ? How did you do it? Thanks for your time.
theogre JUN 02, 02:18 PM
Look at side for old type.
Small wrench fits the nose. I think 9/16" (Somethings Are Not Metric.)



If have AC and Sender on top of engine, Should use second wrench etc to hold the "box" so don't wreck the tube even tho is "bolted down" to engine.

V6 AC can rot like above because pins at top lets "water" inside. Even 88 sender installed this way can have same problem because new Metricpack plug is better "Weather Resistant" but not "Water Proof." Is why TSB to relocate it.

Many failures for old type is leaking diaphragm while rest still "works."
Other times FP switch "burns" or OP resistor wears out.

When FP switch or relay burns... often other things are problems making it burn.
See my Cave, Electric Motors

[This message has been edited by theogre (edited 06-02-2022).]

Rhodesia1977 JUN 02, 10:09 PM
Thanks for the tips. They are really helpful for me. I am far from a mechanic, I am just a beekeeper! I will attempt it and if I think it's not going well, I will take it to a shop. The pics from everyone really helped. I can't believe my Haynes manual had nothing about it! I used to like the old Chilton manuals but don't have one for Fiero. Thanks again. I will let you all know how it goes!
Rhodesia1977 JUN 02, 10:11 PM
One more dumb question! How do I pull off the top with the wires? Is is just a straight pull or some kind of twist and pull? Thanks.