98 XJ no oil pressure according to cluster

[hxcjohnny]

Ok, I'm not getting any reading at all on my oil pressure gauge in my XJ. its a 98 with 110k miles. I've replaced the sender twice and have checked pressure with a mechanical gauge. I replaced the sending unit about two months ago for the first time because my gauge was dancing around and not reading right. That sensor lasted about a month until the second one started doing the same thing. Over the weekend it completely quit reading, so i warrantied it out at Oreillys for a new one. According to my mechanical gauge, Oil Pressure is just under 60 at idle when cold and drops down to 40ish when warmed up, so i know the engine is ok. I did the little cluster test by holding the trip button in while turning the key to the ''On'' position, so I know the gauge cluster itself is work, and I even used electronic cleaner to clean the connection on the sensor.

My question is, has anyone else had this much trouble? If so, what'd you do to fix the issue? The only thing i can think of is to get a wiring diagram and find the pinout on the PCM and run new wires from the sensor to the pcm.

Can anyone help me out on this one before I start wiring crap i dont need?

 

[Flyfisher]

I haven't had that problem, but seems to me that if replacing the sending unit fixes it, then the problem is with the sending unit. Cheapo part? Not sure what they cost, but maybe OEM would be the best bet here.

 

[old_man]

Did you install it using teflon tape. There has to be a good ground through the mounting.

 

[hxcjohnny]

I didn't add any extra teflon, but the sender did have some on it from the factory. Is that causing a ground issue?

 

[98NWCherokee]

Sounds to me like bad sending units. Awhile back I tried to replace mine with one from Schucks.....It was Borg/Warner, which I thought was a decent brand. It literally fell apart in my hands as I tried to install it. I just re-installed the OEM unit and will replace it with another from the dealership. Last I checked, they're around $60.

 

[kastein]

Factory thread sealer should be fine.

Might be yet another flaky sensor, you could also have a wiring issue from the sender to the ECU. ECU to IP is definitely fine since your other gauges work, and all the gauge signals are multiplexed over the CCD bus on 97+.

Try this:
* unplug ECU
* find the pin on the ECU connectors for the oil pressure sender (FSM will help here)
* measure resistance from ground to oil pressure sender wire.

If you see infinite or near zero ohms here, try unplugging the sender end as well next, you should now measure infinite ohms to ground. Then measure end to end on the wire and you should get near zero. Clean the sender connector, maybe retension the terminal wipers, add some dielectric grease and reconnect everything.

If it still happens you probably have another bad sender. They are not very reliable and VERY easy to break so I would not be surprised. I actually bought a wrench (1 5/16" or 1 1/16" iirc) sized for these because I got so tired of putting them in with a pair of pliers and risking cracking the plastic. NEVER tighten them by grabbing anything but the metal portion of the sender.

EDIT: 99 and later also have a special sender, I believe 91-95 are all the same, then some 95s, 96s, 97s, and 98s seem to have their own unique one, not entirely sure. The 99 and up ones are a much improved design that is more like a MAP sensor (integrated electronics and none of the goofy membrane and variable resistor nonsense), sadly not compatible with earlier jeeps.

 

[birchlakeXJ]

Agree with Kastein.

If you get stuck, buy a sending unit from Jeep. There are bunches of threads of people having problem with certain (not all) aftermarket oil pressure sending unit problems.

Count me amongst the group that have problems. Because of that, (and I buy plenty of aftermarket parts) the oil pressure sending unit and the crank sensor are two sensors that I ALWAYS purchase directly from Jeep.

I believe the price of an oil pressure sending unit from Jeep is around $61. Extra money is money well spent in reliability/longevity.

 

[hxcjohnny]

Factory thread sealer should be fine.

Might be yet another flaky sensor, you could also have a wiring issue from the sender to the ECU. ECU to IP is definitely fine since your other gauges work, and all the gauge signals are multiplexed over the CCD bus on 97+.

Try this:
* unplug ECU
* find the pin on the ECU connectors for the oil pressure sender (FSM will help here)
* measure resistance from ground to oil pressure sender wire.

If you see infinite or near zero ohms here, try unplugging the sender end as well next, you should now measure infinite ohms to ground. Then measure end to end on the wire and you should get near zero. Clean the sender connector, maybe retension the terminal wipers, add some dielectric grease and reconnect everything.

If it still happens you probably have another bad sender. They are not very reliable and VERY easy to break so I would not be surprised. I actually bought a wrench (1 5/16" or 1 1/16" iirc) sized for these because I got so tired of putting them in with a pair of pliers and risking cracking the plastic. NEVER tighten them by grabbing anything but the metal portion of the sender.

EDIT: 99 and later also have a special sender, I believe 91-95 are all the same, then some 95s, 96s, 97s, and 98s seem to have their own unique one, not entirely sure. The 99 and up ones are a much improved design that is more like a MAP sensor (integrated electronics and none of the goofy membrane and variable resistor nonsense), sadly not compatible with earlier jeeps.

Thanks, I'm going to get the multimeter out next chance i get. i'm stuck at school for the next week or so and wont have time to work on it. At least i know the engine has pressure, so its safe to drive.

 

[hxcjohnny]

Switched it out last week with a mopar unit and its working great now. Crappy Oreilly parts!