oil pressure fake-out....

so an aquaintance of mine bought an 88 xj, 4.0 4x4 w/ 242.... and he immediate ran into problems, trans, and a valve cover gasket that dumped oil..... So today we fix the valve cover gasket, and now we are getting finicky oil pressure readings. you start it up, it goes to like 20psi, then it slowly starts to drop.... eventually droping to zero... if you rev it up, it raises a little bit, but not back to full 20psi or so. im in a bad situation, because its getting driven to work tommorrow, how do i know? wait for the call that its dead on highway? btw, autozone lists a oil pressure SWITCH... i assume thats the one? hard to beleive its only $13...

I'm sort of having the same problem. I checked to make sure she is pumping oil and it is. When I change the oil my pressure goes up to 30 then drops after it warms up. Is that the same isue your having?
87 4.0 auto

Not to sound like a smart ass but what is the oil level. 88's have oil sender's no?

My oil pressure rarely goes below 40psi, only at hot idle after a highway haul. 60 on cold morning drives.

My pressure 'needle' is currently sitting at 3 o clock . My sender is bad. Didn't start happening until I started having to disconnect it for the oversize 5.0 oil filter.

sounds like the sending unit is bad. easy fix if that is the case.

You want the sending unit for a gauge, not the light which I assume is the "switch". They are not expensive.

I'm not sure where the sensor is on an 88, but on the later models it is right by the filter. Right where you can easily muck it up trying to remove a stubborn filter. (Been there done that) Did you change the oil and filter when you did this work? This could easily explain getting incorrect pressure readings. And Yes. They are inexpensive and easy to swap out.

Not to sound like a smart ass but what is the oil level. 88's have oil sender's no?

Click to expand...

Yeah on a renix it's right by the filter. For my 87 I replaced it, and also mad sure it had oil. It' full. I am wondering if the screen on my oil pump is plugged up, or the pump itself is bad? Is the sender just for the gauge. Meaning can I put an aftermarket gauge in without any trouble with the computer and such?