In my 1988 XJ, sometimes my oil pressure drops to 0 when i turn the ignition to run, and then when i start the engine it goes way past max and stays there... then other times, it goes up then down then back up to max, either way it always ends up maxed out, past 80psi. is the oil pressure sending unit bad or something else like grounds or other electrical bad?

After going on an hour drive on the highway mostly, its now its going in and out of working

 

Could be any of the above. I suggest getting a mechanical gauge and verifying your actual oil pressure and proceed from there,

Basically, the oil pressure sender is a pressure variable resistor. The resistance values to "calibrate" are:

0 (zero) PSI ----- 1 ohm
40 psi ----------- 46 ohms
80 psi --------- 87 ohms

So anything higher than 87 ohms would peg the gauge. Higher as in open circuit. A short to ground would go to zero. So check the wire and the connector.

 

Thanks, the wiring looks fine and all that, the plug is really clean too. I'm gonna look into it more, do some testing. I'm also trying to clean the dipstick ground but I'm having trouble removing it, which is not helping

 

If all the testing mentioned doesn't yield any results, get a genuine Mopar oil pressure sending unit. They are a common failure on the XJ.

A Mopar sending unit will be the most reliable and also the most accurate when mated with the factory gauge in your dash. Good luck and keep us updated!

 

alright thanks for everything! So far so good, i just cleaned the dipstick ground, replaced it with a bolt and washers. Then (completely unrelated im sure) it randomly started working again and hasn't freaked out again yet. We will see. It still looks like its a little inconsistent and has a delayed response time to rpm.