1995 XJ 4.0L Oil Pressure Gauge maxed

[Shoresy_GCo]

Hi All,

The oil pressure gauge on my 95 xj (4.0L) is always pinned at max. It does move a little bit during operation. Does anyone have a good idea where to start to fix this?

Even with no power on in the jeep, it’s above 80, kind of just pointed straight to the right at the screw holding the gauge in.

Thanks!

 

[Rob Mayercik]

Maybe start with checking the instrument panel ground, and the grounds in the engine bay.

links for info:

Renix Ground Refreshing

The Renix era XJs and MJs were built with an under-engineered grounding system for the engine/transmission electronics. One problem in particular involves the multiple ground connection at t…

cruiser54.com

Improving the Instrument Panel Ground

The ground point for the complete instrument cluster on your XJ or MJ is located up under the driver’s side dash. If you lay on your back and look up under there with a flashlight, without w…

cruiser54.com

 

[Shoresy_GCo]

Maybe start with checking the instrument panel ground, and the grounds in the engine bay.

links for info:

Renix Ground Refreshing

The Renix era XJs and MJs were built with an under-engineered grounding system for the engine/transmission electronics. One problem in particular involves the multiple ground connection at t…

cruiser54.com

Improving the Instrument Panel Ground

The ground point for the complete instrument cluster on your XJ or MJ is located up under the driver’s side dash. If you lay on your back and look up under there with a flashlight, without w…

cruiser54.com

Good tip on the grounds! I’ll definitely look into it this weekend.

Do you know if the grounds differ on the 4.0 H.O. vs the Renix significantly?

 

[Ralph77]

In a '96 I used to own it was pegged too.
I just ignored it.
Engine wasn't making any weird noises so....
In my '00 that happened too.
Replacing the sensor fixed that.
Having said that I would check grounds and wiring to the sensor itself first like everybody else said.

 

[Ol Blue]

Replacing the sensor fixed my issue. Maybe try jiggling the connection and give the oil pressure sensor a few taps. Mine would read true momentarily if you tapped it just right.

 

[Rob Mayercik]

Good tip on the grounds! I’ll definitely look into it this weekend.

Do you know if the grounds differ on the 4.0 H.O. vs the Renix significantly?

Probably, but I've never owned a Renix so can't say for sure. Your 95 should be the same as my 92 for engine bay grounds - a body ground near the battery, the dipstick mount grounds, and a braid that runs from the rearmost bolt on the valve cover (driver's side) to the firewall. Think the starter grounds to the bellhousing/block, but not sure.

Instrument panel ground should be similar to the Renix, I would imagine.

 

[Saudade]

You can test the sender with an ohm meter. Take the connector off and check from the terminal on the sender to ground with the engine off/key off. At 0 psi, the resistance should be 1 1 ohm (essentially continuity). If significantly higher or even shows Open Loop, the sender is bad, or you've chosen a bad ground point.

You can also start the engine and measure the resistance. You can interpolate to estimate your oil pressure based on the ohms measured. Of course, if it's still way high, it's bad.

40 PSI should be about 47 ohms
80 PSI should be about 89 ohms

So the higher the ohms, the higher the PSI reading. So if you have a bad ground (very high to infinite), the gauge would peg. Just like if the sensor is bad (open circuit internally) you'd peg the gauge.

You can verify you have oil pressure removing the sending unit and put in a mechanical oil pressure gauge so you know what you actually have.