oil pressure problem

Well i recently picked me up a 99 xj with the 4.0 in it. Previous owner was running synthetic oil in it and it needed an oil change. Prior to changing the oil it would hold good oil pressure when it was cold but when it got warmed up it wouldn't read anything on the gauge and it would go to zero and the check gauges light would come on.

Now last night i went and did an oil change on it with a new napa filter and 10w 30 oil. Now the gauge will not come off of zero and is reading no oil pressure. Does anybody have any ideas what could be causing this and maybe an easy fix for it? I know that it has plenty of oil in it but its not reading on the gauge and don't want to risk hurting the motor or anything. It is still running great with no knocks or pinging or anything. Any help would be great.

Thanks,
Ben

Next to filter is the oil sending unit, check to see the wire is still on and tight. Some times the sender can get full of crap an make it hard for the oil to pass into it, you may need to clean the area up.Look for a write on this, i heard about it on here a couple days ago.

HTH

The Oil Pressure Sensor (Next to the Distributor - towards the firewall) may have been damaged when the oil filter was changed. Check the connector and the sensor for damage.

Ok i will take a look at it after work. Would there be that much of a difference in pressure readings going from synthetic to regular motor oil? What should i look for if the sensor is ok?

Jeepguy91 said:

Ok i will take a look at it after work. Would there be that much of a difference in pressure readings going from synthetic to regular motor oil? What should i look for if the sensor is ok?

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Viscosity and/or Dino vs. Synthetic should not make any marked difference...it hasn't on any of my vehicles.

If you change the sender and are still having pressure problems it's likely time to drop the pan and either change the oil pump or just clean out the pick-up screen...but, I wouldn't worry about it too much, it's a 99% chance that it's just the sender. I've never had to change an oil pump in over 300K miles.

Even changing the oil pump is simple, the hardest part is dropping the pan, the pump is just 2 bolts and a wimpy gasket.

If you DO drop the pan, replace the OP gasket with the one piece Fel-Pro rubber gasket, not the 4 piece cork one...well worth the extra $$

Well started jeep up after work and it held 40lbs of pressure with no problems. As soon as i started driving it for a bit the gauge started going up and down. Whenever i came to a stop it would go to zero but when i gave it gas it would start to come back up. Part of me thinks that it might be the pickup screen being plugged or maybe the pump. It just doesn't make sense to me how it could hold great oil pressure last night and not have anything today. Going to try and pick up a new sensor tomarrow for it.

What synthetic, need the specs, was the PO using, and which one did you use?

Miles?

Check the did stick for coolant?

Pull the oil filler cap and see if oil is getting to the top side.

Pull the sender and use a pressure gauge to verify oil pressure.

If the oil pressure sender reads zero or infinite ohms to ground (engine block) using an ohm meter (with the engine off, and the sensor wire disconnected) it is bad.

1. TEST IT. Buy or rent a mechanical oil pressure gauge, remove the sensor, test your oil pressure.

2. IF THE OIL PRESSURE IS GOOD with the mechanical gauge, try and verify the wiring connection and/or replace the sensor.

3. IF THE OIL PRESSURE IS NO GOOD--well, you might have to pull the pan and consider replacing the oil pump and/or gauging the crank bearing clearances.

The oil sending unit for the gauge is right by the oil filter adapter housing. If you're not careful, you can damage or jar it while removing or replacing the oil filter. Check this real close before you do anything else. A bad sender can fluctuate all over the place, stay stuck at 0, sometimes they will peg out all the way to the right as well. The sender is 30 bucks at o'reilly's, but lots of times you just need to unplug and plug the connector back in to get the gunk off the connector. If the connector is damaged or questionable at all on the end, cut it off and put a new one on.

[EDIT]: Make sure the sensor is not damaged or leaking oil out of it as well. I've seen this happen after an oil change as well.