So I have a 97' 4.0l and the oil pressure gauge fluctuates almost to no pressure at idle and when I start driving it goes back up , I have replaced the oil pressure sending unit twice and same problem , also checked the volts with a meter and its not the wiring. I called a Jeep dealer and asked what the pressure at idle should read , said he didn't know but from the sounds of what's happening he said sounded like a cracked head. Doesn't leak coolent either. I hope this isn't the issue.

 

13psi is the minimum recommended oil pressure at idle. Rent a manual gauge and screw it in where the sender is. It's normal for the oil pressure to go up while accelerating. Your dealer sounds like a bunch of idiots.

 

"said he didn't know but from the sounds of what's happening he said sounded like a cracked head."

^^^^^^^^^^^^^^^^^^^^^^^^^
Too funny!!! Could also be worn brake pads.....

 

could be a faulty gauge, as stated get a mechanical gauge for like $20, install it where you can watch it while you drive temporarily, and see what you oil pressure really is.

 

Couldn't I just rev the throttle from under the hood while watching the gauge?

 

Ahhh the brakes are starting to squeak a little...^^^smartass^^^

 

Yes.

Might also unscrew that oil sender again and clean out the oil passage that feeds it.
Any lifter or valvetrain noise at idle when the pressure reads zero?

 

"bring it in, we'll fix you right up".

 

When I replaced it the 2nd time I made sure I cleaned the passage out first. The engine doesn't make any clicks , clunks or taps , its at 170k and runs great besides that issue.

 

I have found that the best thing to do is drive the truck, which will get the oil at it's hottest temp compared to idling, and see where your pressures are at cold start up, hot idle, and hot cruise.

 

Then I doubt you really have zero oil pressure. Buy, rent or borrow a mechanical gauge and see what it reads.

 

Another thing I failed to mention , years ago after I first got it , I was changing the oil filter and slip and snapped the sending unit off , I was able to get the other part out then after the new one is when it started doing it. And it doesn't leak or burn oil. I will do the manual gauge method and see , thanks guys.