High Oil Pressure

1994 XJ 4.0 200k miles. Stock daily driver.

I do not have access to a mechanical oil pressure tester.
I'm not an experienced mechanic, so I don't know what to do next.

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My oil pressure is not reading normally anymore. For the life of the vehicle, the gauge has read from 15 to 40 psi. Now, it never drops below 50, even at idle with a warm engine, and peaks at 60 when revving up.

Other than that, everything appears to be normal. The Jeep seems to drive the same, and the engine sounds fine.

I get the expected results when disconnecting and grounding the sensor wire.

I replaced the oil filter, and installed a new sending unit. Nothing changed. So I tried yet another new sending unit, still no change.

I have tested both new senders with an ohmmeter. The impedance still never drops below ~50 ohms.

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Can anyone tell me where to go from here?
Could I actually be experiencing a problem in the lubrication system?

Is it possible that I may damage the engine if I keep driving?

Likely needs the oil sending unit replaced. Get a Mopar one since the cheap Chinese ones are known to fail quickly.

How high is the oil pressure, hot vs. cold?

My first thought would be a ground issue with the sensor or gauge cluster causing an offset.

Oil pressure test kits are not expensive and can be bought online.
https://www.harborfreight.com/engine-oil-pressure-test-kit-62621.html

From your description, it's probably a wiring problem.

Ok, lets assume the pressure sender is good, you say you tested it ohmed ok.

Next to check is the wiring and gage...

Per my 1990 XJ factory service book

With 1ohm resistance at sender, you should get gage to read 0 psi, +/- 2%
With 46 ohm resistance at sender, you should get 40 psi, ×/-3.5%
With 87 ohm resistance at sender, you should get 80 psi, +/-3%

So go get a 46 ohm resistor at the electronics store, place it one end to engine ground, other end to the sender wire (sender removed). If you are not getting close to 40 psi, then problem is in the gage and/or wiring, connections. A 50 ohm resistor would work too, but then the gage will read a tad more than 40 psi.

This resistor can be a small low watt resistor, it will be flowing very little current, so low watt is fine.

The factory book lists the ohms value and gage deflection for all the applicable gages, ie.. fuel, temp, pressure.

good luck

Corrosion on contacts will always lead to an increase in resistance. I would do the following first:


1) remove the sensor wiring and try to clean the contacts really well - until you see bright copper.


2) remove the instrument panel from the Jeep and using a pencil eraser, rub the copper contacts on the panel (where the wires connect) until they are shiny. Do the same for the "wire side".


If the issue is that some corrosion has occurred, this should cover the two most likely areas which should bring the measured resistance back down to where it should be.



HTH
Todd

Black1990jeep said:

Ok, lets assume the pressure sender is good, you say you tested it ohmed ok.

Next to check is the wiring and gage...

Per my 1990 XJ factory service book

With 1ohm resistance at sender, you should get gage to read 0 psi, +/- 2%
With 46 ohm resistance at sender, you should get 40 psi, ×/-3.5%
With 87 ohm resistance at sender, you should get 80 psi, +/-3%

So go get a 46 ohm resistor at the electronics store, place it one end to engine ground, other end to the sender wire (sender removed). If you are not getting close to 40 psi, then problem is in the gage and/or wiring, connections. A 50 ohm resistor would work too, but then the gage will read a tad more than 40 psi.

This resistor can be a small low watt resistor, it will be flowing very little current, so low watt is fine.

The factory book lists the ohms value and gage deflection for all the applicable gages, ie.. fuel, temp, pressure.

good luck

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