Try cleaning the connections and check your dash ground. I believe you can find the ground wire for the dash at the dash speaker on the driver side.

 

The dash pod is mounted with fixed connectors, I would pull the pod loose and exercise the connections, possibly the connections have corroded.

I too have had oil pressure gauge issues as most here have had, remember these engines have 'Hydraulic Valve Lifters' if you had no oil pressure, the lifters would collapse and you would hear a lot of clatter under the hood almost immeadiatly when there is no oil pressure.

 

Thank you for the responses. I know the oil pressure itself is ok as the engine runs well and sounds good. I will dive into the dash tomorrow and see what I find and update it here. What is puzzling to me is how changing the sending unit has temporarily solved the problem twice now.

 

After taking out the instrument cluster it seems that there may in fact be a grounding issue. There is a large ribbon-like grounding cable connected to the bracket which the instrument cluster connects to. The cable is connected to the bracket at one end as show in the attached pics. However the other end is literally connected to nothing. Now my problem is that I can't seem to locate where it should actually bolt into place... Anyone know where it goes?

 

You have to use the Mopar switch and no aftermarket switches. It was a nightmare changing out the auto zone switch every time and never working . I wasn’t sure after manually checking oil pressure what the problem was. I talked with my mechanic and he said it was the switch u just have to use mopar. I went to the Jeep dealer and got the switch for $104 and took the switch back to auto zone and they did give me my money back. The mopar switch did the job

 

I don't know where it was suppose to go, how long is it, and can you find a good ground w/ screws to mount it to?

 

I am just going to attach it to the firewall and see if it fixes my issue. I cannot find a bolt that matches the size of connector on the end of the ribbon wire anywhere within the 2 foot length of the ribbon wire.....

 

Still at zero pressure on gauge

The ribbon cable is attached to a bolt on the firewall now at one end and to the bracket that holds the instrument cluster on the other. I believe this ribbon cable may have gone to the factory radio originally but it's a guess.

I checked the instrument cluster by holding the odometer reset while putting ignition to on and it passed all. I cleaned off the connectors for the instrument panel and very slightly bent the prongs with needle nose pliers to insure a tight connection. I reset the ecm as per instructions on this site. Started up the jeep and it still runs/sounds great but instrument cluster gauge still reads zero.

I decided to disconnect the wiring harness to the oil pressure sending unit to see if maybe this was not seated correctly. I noticed that there is visible engine oil in this wiring harness although I have no idea if it SHOULD be there. Started again after cleaning off this wiring harness and still shows zero. The harness seems to be in good shape and snaps into place nicely.

I still show zero pressure and it seems I have run out of things to try. Any ideas?

 

Any ideas?

Hi Zicknak,

Wondering if you had any resolution to this old oil pressure gauge issue? I'm experiencing the same issue and have replaced the sender which only solved the problem for a few months. I'm showing (intermittently) max pressure and then no pressure, then max etc. Seems random and is inaccurate as engine is just fine.

Thanks,

Scott.

Sent from my HTC U Ultra using Tapatalk

 

I have a similar problem on a 2017 JK, the engine light comes on, the computer scan says bad oil pressure sending unit, I replace it, 150 miles later back to square one.

What will fix this?

Jim

 

Out of curiosity, do you also have an oil temperature gauge?

Sent from my HTC U Ultra using Tapatalk

 

My gauge went to 0 while on the interstate. Turns out it was a faulty oil pressure switch. Pretty easy fix and 40 bucks.

 

Thanks weldit, yeah we've replaced the switch already, however the issue just recurs again after a while. I'm now investigating electrical issues, and possibly some sort of interference with the a possibly faulty oil temperature gauge probe plugged in near the pressure sender.

 

This is, unfortunately, a common issue. I hooked up a mechanical gauge to my 2000 4.0l, and while the pressure does drop off quite a bit when warm, it still reads about 5-7 PSI at idle, which is essentially the minimum the engine should have (10 PSI per 100 RPM). It comes up as I drive it.


I don't think the factory gauge is equipped to read such low pressure at idle, and just drops to zero, even though it has 7 or 8 PSI at idle. When cold, my pressure is up near 60.

 

Same Issue, any resolutions?

1998 TJ
Hey fellas, I'm having the same issue. My oil pressure was reading 40 at start up and it would slowly go down until it was at 0 as it was warming up, my check gauges light was also coming on once it would get down to 0. I replaced the sensor and now it is always at zero, pressure never moves even with a cold start up. Traded sensor in for another new one thinking it was just a bad sensor and the new one is still doing the exact same. I'm at a loss.

Thanks, Dylan

 

1998 TJ
Hey fellas, I'm having the same issue. My oil pressure was reading 40 at start up and it would slowly go down until it was at 0 as it was warming up, my check gauges light was also coming on once it would get down to 0. I replaced the sensor and now it is always at zero, pressure never moves even with a cold start up. Traded sensor in for another new one thinking it was just a bad sensor and the new one is still doing the exact same. I'm at a loss.

Thanks, Dylan

Welcome to the Forum.

 

In my case on a 99 TJ, the solution was to replace the actual wiring harness that connects to the oil pressure sending unit... If you see oil getting into the harness that connects to your sending unit (I did), this is most likely the solution. It's been several years now and gauges/check engine light are still fine.

 

Fix low oil pressure after engine warms up trick

I was seeing my oil pressure drop to 5 and below after the engine warmed up with no tapping sounds and I replaced the oil pressure switch as well with no change.
What worked for me, and I saw recommended by someone else, was to try blowing out the oil from behind the oil pressure switch for a few seconds. I took the oil pressure switch to Homedepot to get the thread type (I don't remember thread size but attached a picture) and then went over to the plumbing section and bought this brass piece and some rubber hose shown in picture. I screwed this on the block in place of the pressure switch and ran the tube into a bucket and started the engine at idle for 10 seconds, then gave the engine one quick rev and shut it off.

I topped off the oil again and my oil pressure was fine after that. Unfortunately I had already ordered a new oil pump and my rear main oil seal was leaking so I replaced both a month later. But that first trick really seemed to work.

 

When you blead the oil pressure switch port on the block, did you get any sludge out or was it only motor oil?

 

Nothing stood out as the cause as I pored the oil from the bucket into the my recycling container. Maybe I should have pored it into a pan first. At that point I had not started it yet. But changing the oil and changing the oil sensor did not make a difference to the oil pressure dropping after it warmed up.

 

Thanks for posting this. I have the same issue on my 4.0 with only 105k miles on it. All Blackstone reports have come back clean. I refuse to believe that every rig that has this problem are worn bearings.


My question, did you blow the oil out when engine was warm (i.e. showing low pressure) or cold?

 

two issues,
Yes the oil pressure senders, both Mopar and after market are trash.
I went to 15w/40 Rotella, and my problem with hot engine oil pressure at idle went away....at least for a while, I'll let you know.

 

To answer whether the oil was warm or cold when I flushed the oil out the oil sensor hole, I don't remember. I think it was cold. My guess is there was either an air bubble, or sludge in the oil pump, in behind the pickup screen, which feeds that sensor. Like I mentioned it was someone else's trick I read about and it seemed to work for me. My part was finding the tubing and brass fitting at Home depot which made the job a lot less messy than just blowing oil out in the engine bay. I'd say try it cold first so you don't get burned. You can always try it again warmed up if needed. Hope it helps. Really changing the oil pump isn't all that hard either but that is messy a getting the oil pan back on is easier with two people.