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Wired Wrong 12-13-2010 06:13 PM

Check Gauges/Zero Oil Pressure
1999 Grand Cherokee 4.0 4x4 auto.94,000 miles. Recently when at stop the check gauges light comes on and the oil pressure drops to zero,When you accelerate the light goes off and the oil pressure rises.This only happens on very cold days (below freezing).Once the temps outside warm up this does not happen.I am thinking the oil pressure sending unit may be going out.The engine runs fine ,no knocking etc.

cheapjeep 12-13-2010 07:20 PM

Re: Check Gauges/Zero Oil Pressure
Yeah 94K isn't much on these motors. I'd try a new sensor and change the oil and use a good filter. You could have a filter issue because you would think your pressure would be higher not lower in cold weather.

Frango100 12-13-2010 07:22 PM

Re: Check Gauges/Zero Oil Pressure
As long as the engine sound doesn´t change, its most probably the oil sending unit. Change it ASAP, just to be sure that not something else is wrong and would ruin your engine.

Wired Wrong 12-13-2010 08:31 PM

Re: Check Gauges/Zero Oil Pressure
Thanks for the replies.I only use Wix or Napa Gold filters and Valvoline oil.I never go over 4000 miles between OC. Oil and filter only have about 2000 miles on them.I think I am going to check the sending unit first and go from there.Thanks again.

atommota 12-15-2010 03:16 PM

Re: Check Gauges/Zero Oil Pressure
Did it turn out to be the filter or sending unit? I'm having a very similar problem (2000 WJ 150k miles) I get zero pressure in very cold weather, some times the throttle will bring the pressure up, sometimes not. I have a new oil pump, but its behind 8 hours of labor so I'd like to make sure that its not a filter or sensor first.



Wired Wrong 12-15-2010 04:55 PM

Re: Check Gauges/Zero Oil Pressure
In the shop now,Think it is going to be the oil pressure switch, from what I can find from talking with people.I will post results later.

svt393 12-16-2010 07:39 AM

Re: Check Gauges/Zero Oil Pressure
Same thing happened to me ended up being the sensor. Only use oem mopar sensor the napa and advanced sensors were crap and didn't work right.

atommota 12-21-2010 09:22 AM

Re: Check Gauges/Zero Oil Pressure
good call svt393...i had a discount at advance auto to use so i thought what the hell ill get the sensor there. Turns out it is wired in reverse. RPM goes up, Oil Pressure goes down...I plumbed in a T fitting to a mechanical gauge and sure enough, pressure actually goes up with rpm like you would expect. Pics of my setup here if anyone is curious.

Now I have to convince Advance to take the sensor back...I might just drive over there with the gauge attached to my windshield and tell them we are going for a ride if they wont take it back.


atommota 01-03-2011 09:27 AM

Re: Check Gauges/Zero Oil Pressure
ahhh replying to myself. :)

anyways, just wanted to confirm for anyone who might come across this in the future...It was indeed my sender unit, and as mentioned earlier, the advance auto sensor is wired backwards, but the OEM jeep sensor solved the problem immediately.

Advance auto took their sensor back, no questions asked...but it may have helped that I am kind of a regular in the store.


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