99XJ4.0

Hey everyone I wanna see if anyone else out there has seen the problem that I am having hopefully someone me can give me some ideas on which direction to go. I just bought a 99 XJ with a 4.0 and the oil pressure gauge doesn't seem to be working. I could not find my manual gauge but I am confident that the engine has oil presure because it sounds good and when I pulled the sending unit and cranked the engine oil came out. What the gauge does is the needle always seems to stop just before the the first line so about 8 lbs. When you shut the key off the needle returns to zero and I have done the gauge test where you turn the key on while holding the odometer trip reset button and everything seems to work. Also when you turn the key on without the engine running the gauge also reads about 8lbs once again and with the sending unit unplugged the gauge goes to zero and the check gauges light comes on. I have tried using two other sending units with the same result. They were both used ones but I highly doubt that three sending units would do that exact same thing. I have even gone as far as to try a whole different gauge cluster that I had lying around with the same result. Does anyone have any ideas on where to even start troubleshooting? Any ideas would be appreciated.

Pigeon

My mechanic rating would land somewhere in the Moderate Shade Tree range. It may be a wiring issue. There may be a plug near the firewall that has the sender wire in it. If so, you could isolate it and do a continuity and resistance check. I believe if the wire has been compromised it could cause this issue. The gauge could also be defective, even though it passes the self test. Hopefully someone with better experience will be along soon to help. This link is to a free online factory service manual. It is for a 1997, but the wiring may be the same or very similar. I hope this helps.1997 XJ Service Manual

Pigeon

This is a 97 parts list. 97 XJ parts list

dave1123

LGBT= Liberty, guns, beer, and ****.

If the 99 still uses an old school gauge, clean and tighten the 3 nuts on the back of the gauge. There is a shunt resistor in the delta circuit inside the gauge that may have come loose.

99XJ4.0

Thanks for the info I doubt if the problem is in the gauge though since I tried a spare gauge cluster that I had and got the same result and I looked found four phillips screws directly behind the oil gauge. If I can't figure this out I my pull the original cluster back out and check them.

99XJ4.0

I thought I would post an update and maybe it will help someone in the future. I did some more research about the wiring and found out that the sending unit has three wires one of the outside wires should have ground going to it and the other outside wire had 5 volts going to it. Which leaves the middle wire which is the signal wire and I checked my plug with a volt meter and I had the correct ground and voltage so I decided look up some wiring diagrams before tearing the wiring harness all apart in an attempt to find a problem with the signal wire and lo and behold the signal wire goes the the pcm which then tells the gauge what to do. I happen to have another 99 xj which is a parts Jeep and I took the pcm out of it and put it in my good Jeep and started it up and the gauge worked perfectly so if anyone else is having problems with their oil pressure gauge the sending unit is usually the problem but if its not and before you tear you wiring harness apart check your pcm. Thank you to everyone for the advice.