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Unread 10-12-2008, 01:10 PM   #1
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2006 WK 
Join Date: Oct 2008
Location: San Antonio
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High oil pressure - 2001 Cherokee 4.0

Hi, all.

First, I also posted this in the Comanche forum...so I apologize for double posting something - just want to get this in the right place.

Second, I'm new...so I'll introduce myself first. I live in San Antonio and own a 2001 Cherokee Sport 2x4 that mainly serves as a glorified station wagon to haul my kids and big dog around. I've had her since she was new...and she has about 115k miles on her. She's simply been the very best vehicle I've ever owned.

But she's a bit under the weather right now...at least I think she is.

Started her up this morning to go to the gym. Normally, her oil pressure is around 30 when idle...revs up to about 45-55 when under a acceleration onto the freeway. Today, however, she started out running at 45 when idle - and pegged at 80 when I was accelerating.

Worried about damaging my Jeep, I turned around and went home.

I let her sit for about 30 minutes and then started her up. Revved the engine up to about 5k RPM and she only pegged up to 60 on oil pressure. After reading my owners manual, I found that 60 is the top end of normal range. Thinking I was OK, I took her over to the gas station and filled up. Problem returned...she was pegged at 80 the whole time I was hitting the gas.

Took her back home and let her sit for a while, wiped down the sending unit and started her back up. Let her run a bit, then revved her up to 5k RPM...back down to 60 max on oil pressure.

So...took her around the neighborhood and opened her up on the two lane that goes through the subdivision. Still only at 60 max on oil pressure.

Next, I expect that she'll be back at 80 when I fire her up to go to work tomorrow.

Bad sending unit?

Or something far worse?

For what it's worth, she's had her oil changed religiously every 3500 miles and had her last oil change two weeks ago. It does look like the oil change guys were pretty sloppy that day...there was oil on the sending unit...and I had a drip on my garage floor. In addition, my wife had the oil changed on her 2007 Pacifica the same day at the same place...and they failed to screw the plug back in all the way.

I look forward to hearing from you guys...and contributing my lessons learned as I get the chance.


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Unread 10-12-2008, 03:17 PM   #2
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1997 XJ Cherokee 
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Mine did the same thing. It was the sending unit. It's a very common problem.
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Unread 10-12-2008, 04:38 PM   #3
It's the crank sensor!
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1999 XJ Cherokee 
Join Date: Nov 2007
Location: Central Minnesota, MN
Posts: 8,434
Definitely suspect the sending unit (aka: oil pressure switch in some parts stores) It is one of the most common hardware failures on the 4.0 and replacements are cheap. I recommend purchasing one directly from Jeep for best accuracy with your factory gauge. I've had mixed luck with aftermarket sensors. If you have the ambition, you can install a mechanical oil pressure gauge where the sender goes to verify your pressures. They aren't too expensive or some of the big box auto parts stores rent them and the adapters needed to mate up properly. Good Luck!
99 Cherokee, 4.0 AW4, NP242
Past Jeeps: 49 Willys, 81 Scrambler, 88 Comanche
Without "data", all you have is an opinion!
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Unread 10-12-2008, 05:36 PM   #4
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Thanks, guys.

I'll swap it out as soon as I can find one at the local auto parts store. The motor sounds fine - and none of the idiot lights are going off - so I am hoping it's the sending unit providing bad data to the gauge. More to follow.

Jeep on!
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Unread 10-12-2008, 06:09 PM   #5
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1998 XJ Cherokee 
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Even if you had no oil pressure your jeep will still run. We had a 4.0L that was about to be scrapped and we drained the oil replaced it with windshield solvent and removed most of the coolant. We then took it for a ride for about ten miles before the outragous smell made us come back. We then let it idle in the driveway for another 20 min. or so, occasionally reving the gas. it was begining to get pretty noisy in the lifter area and a horrible yellow smoke was coming out of the outta the oil fill hole. We finally shut it down when the scrap yard wrecker got there. The driver had a good laugh as he hauled the still smoking wreck off to the junk yard. Best part, we still got 100 bucks because she was still drivable. I dont think your Jeep will mind too much pressure.
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Unread 10-13-2008, 07:11 AM   #6
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I checked the Jeep before starting the motor this morning...the oil pressure read at 15 before I even turned on the motor. Then, as I was driving...it initially spiked up to about 75, but dropped down to 60 the balance of my commute.

I'm really thinking this is a bad sending unit now.

Think I'll blow it off until our next holiday weekend and swap it then.
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Unread 10-13-2008, 12:14 PM   #7
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Mine did the same thing a few years ago, thought about replacing it but after a few months it leveled back out. Still reads about 5 PSI higher than it did the first 7 years (at idle and at highway).
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2000 Sport 4X4 4.0 inline six, AW-4 Automatic, stock
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