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Oil Pressure Pegged Out

Dacrane

NAXJA Forum User
Location
Calera, Alabama
Hey guys, long time lurker, first time poster. Gotta say, this forum had been invaluable in keeping my XJ running. So, I have a bit of an issue that I can't seem to figure out and I was hoping someone might have a suggestion. My oil gauge is pegged out at 80+ psi. I know it's not that high since it has been running this way for months. The old gauge was bad when I got it. I finally got around to replacing the sender, but it still does the same thing, however, now when I turn the key on, but the engine off it defaults to 0. This didn't happen with the old one. I have searched other threads, but they all boil down to replacing the sender which I have already done. My XJ is a 96 with the 4.0. thanks in advance!
 
can you check with a mechanical gauge? Maybe your OPRV is not working and pressure really is that high?

And yeah, usually if the gauge reads high, it's the sender. I ended up ordering a gauge set because nobody at my friend's shop had one, and guess what, it was the sender.
 
I like to test with a mechanic gauge first. Maybe a defective sending unit. Mopar ones tend to work better.
 
Be weary with non oem electronic pieces. I have had bad luck with them. bought 2 crank position sensors that were bad early this year...

junkyard oem replacements seem to be the way to go.

but then again. I bought 2 or 3 $10 or less ebay sensors. and they have worked fine.

but +1 on the mechanical gauge test. because you could have a blocked oil port which in the long run will cause oil starvation. so be careful with this.
 
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Thanks for the tip on the manual test. I will run by harbor freight today and pick up a test kit. The sender is just a Borg Warner from eBay, so that could be it. I'll test it and report back.
 
The oil P sensor is basically a variable resistor, and you can test it with an ohm meter. Disconnect the wiring lead and test from the battery ground to the sensor contact post. See if it changes from engine off (0 pressure) to engine running. That should tell you if it is a wiring issue. The FSM should list the proper resistance values if anyone has one handy.

Also there should probably be some thing like 5 volts at the wire, engine running, sensor wire when disconnected.

I had a pegged 80 Psi reading once on mine that was busted Cat converter, backing up the exhaust. New Cat fixed the low power, and other issues and of all things fixed the oil pressure reading. Never that before or since....
 
Thanks for the replies. I picked up an oil pressure test kit from harbor freight and checked it through the rpm range. At idle, warmed up I have a little over 10 psi. At the top end I have 60. What is weird is that once it warms up and I come to a stop it reads 0, but as soon as I give it any throttle it pegs out. Couple be a bad sensor, but I'm thinking wiring. I will test the sensor and if it is working then I will just get a mechanical gauge and mount it in front of the stock gauge. I really don't feel like trying to go through 20 year old wiring. The cat is something else I will need to check since as far as I know everything is original and it has over 250k miles :D
 
You need to worry about that 0 reading at idle hot with the mech gauge, as that is no good either for the engine.

I suggest changing the oil filter next ( it may be bad, plugged) and clean out the port on the P-sensor threaded connection, reinstall it and tests again, it may have trash in it.

There is an old thread somewhere about the sensor port and the PRV clogging and how to unclog them Cruiser54 may have it?
 
It is at 10 with the mech gauge, 0 is on the stock gauge. It is about time to change the oil anyway, so I will run some seafoam and clean the ports as well while I have it drained.
 
Much Better but 12-13 is the OEM spec minimum at idle.

What oil specs are you using.

What brand is the new sensor?

It is at 10 with the mech gauge, 0 is on the stock gauge. It is about time to change the oil anyway, so I will run some seafoam and clean the ports as well while I have it drained.
 
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Right now it has 10w-30, but this change I am going to run some 15w-40 shell rotella diesel oil to try to clean out some of the sludge. There new sensor is a Borg Warner
 
I have been trying to figure out the same problem on my 96 xj. As soon as I start it the OEM gauge pegs out. Runs fine. Have changed sensors, cheap and OEM mopar works for a day or so then pegs out. Thinking wiring.
 
Check the plug and the wires going to the sendibg unit. They get warm and the insulation gets btittle over time. My 96 does the same thing and i know for a fact its my plug/wire
 
The sender is a variable resistor as stated. The gauge has a coil that creates a magnetic field when its charged with current, and the sender is on that circuit. As sender resistance changes the magnetic field changes, stronger / weaker magnetic field.

If you disconnect the wire (open circuit) the gauge should fall to bottom. If you touch the sender wire to ground (no resistance) the gauge should peg to the right. If that doesn't happen the gauge is broken.

Oil pressure sender resistance is about 1 ohm per psi. Simple test is use a multimeter between the sender and an engine ground and see what it says. If the gauge is far off but working, the gauge cluster ground is probably screwed up and adding more resistance.
 
The sender is a variable resistor as stated. The gauge has a coil that creates a magnetic field when its charged with current, and the sender is on that circuit. As sender resistance changes the magnetic field changes, stronger / weaker magnetic field.

If you disconnect the wire (open circuit) the gauge should fall to bottom. If you touch the sender wire to ground (no resistance) the gauge should peg to the right. If that doesn't happen the gauge is broken.

Oil pressure sender resistance is about 1 ohm per psi. Simple test is use a multimeter between the sender and an engine ground and see what it says. If the gauge is far off but working, the gauge cluster ground is probably screwed up and adding more resistance.

Didn't something about that gauge direction change in 1991? Nice info!!!
 
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