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Old 11-10-2011, 05:37 PM   #1
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Oil Pressure drops to 0 when Idling

The oil pressure in my '97 2.5L just recently started dropping to 0 and tripping the 'check guages' light whenever idling or when I hit the brakes. Mileage is 123,xxx. Engine temp hot/cold does not make a difference. Pressure returns to normal 30-40 psi when engine is revved... Coincidentally, at the same time the oil pressure started dropping, every few times I try to start the Jeep, she will not idle unless I keep the throttle open. I think the oil pressure issue is the sending unit but wtf would cause it to intermittently not idle when started unless throttle is held open?? Plugs & Wires going bad?

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Old 11-10-2011, 05:44 PM   #2
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I had the same problem with my 4.0. All it was was the oil pressure sensor...Replaced it and everything was fine!

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Old 11-10-2011, 07:00 PM   #3
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I think everyone has replaced the oil sending switch at least once.
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Old 11-11-2011, 05:34 AM   #4
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I'd start by checking my oil pressure with a gauge (take out the sensor, fit a PSI gauge and start her up).

If it realy drops to '0'...you may want to drop the sump and check your rod bearings. If those are ok, you may have an oilpump problem.
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Old 11-11-2011, 05:39 AM   #5
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mine drops when i brake hard. enging check alarm sounds then pressure climbs right back up.
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Old 11-11-2011, 07:51 AM   #6
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If your engine had 0 oil pressure it wouldn't be running for more than a few seconds! It's the sensor...they all go bad. That is the reason that Jeep went away from the gauge and did the idiot-light instead.
Change it out!
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Old 11-11-2011, 12:23 PM   #7
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I had to change the sending unit on my old 77 Power Wagon every year or 2 like clockwork. It would get where it read 0 at an idle and about 15 at 60 MPH. Most vehicles will have the problem eventually, just some are more prone to it that others.
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Old 11-11-2011, 01:04 PM   #8
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Quote:
Originally Posted by Punisher-One View Post
If your engine had 0 oil pressure it wouldn't be running for more than a few seconds! It's the sensor...they all go bad. That is the reason that Jeep went away from the gauge and did the idiot-light instead.
Change it out!
This same thing is notoriuos on the Ford Rangers, and why they too went to an idiot 'gauge'. It always point to the same direction, or doesn't point at all.
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Old 11-11-2011, 10:56 PM   #9
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Our old 64 CJ did that the whole time we owned it but i dont think the new jeeps are supposed to do that.
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Old 11-14-2011, 05:24 PM   #10
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@bagged92sdime: Good to know I'm not alone. $25 from Napa for a new one. Gonna put it in 2nite.
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Old 11-15-2011, 10:17 AM   #11
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Not trying to hijack this thread, but what if I have the same problem with my 2002 4.0L however the oil pressure rises as the engine rpm is increased and drops again at idle? Would this point more towards an oil pump problem instead of a sending unit problem?

Again, sorry for the hijack
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Old 11-15-2011, 11:40 AM   #12
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Oil pressure should rise with RPMs. Does it drop to zero at idle or does the max pressure drop the further you drive it? If so replace the sending unit.
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Old 11-15-2011, 11:49 AM   #13
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If the oil sending unit is bad, does that mean the gauge is reading wrong or does the pressure actually drop? If its just an incorrect reading due to the sensor gone bad, then the pressure only appears to be low, when in fact it probably is good, is that correct?
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Old 11-15-2011, 11:55 AM   #14
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The sending unit just tells the gauge what to display.
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Old 11-15-2011, 12:46 PM   #15
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psi rises with rpm and stays just below 40psi and only drops to zero at idle.

Is this a normal reaction of a bad sending unit?
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Old 11-15-2011, 01:01 PM   #16
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Yes.
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Old 11-15-2011, 02:00 PM   #17
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The stock sending units are crap. Hook up an actual Gauge make sure it really isn't going to zero. If not either replace the sending unit or leave the gauge in it so u know what its really at.
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Old 11-15-2011, 09:51 PM   #18
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The sending unit was in fact bad. The wire harness clip was full of oil, however my battery also went bad at the same time and this threw me for a loop because of the way the gauges were reacting. My 2006 Dodge Ram Megacab acted the same way when one of the batteries went bad, i.e. gauges started acting up and indicating erratic values. Thanks for helping me stay the course with the sending unit
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Old 11-20-2011, 12:56 PM   #19
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I think my sending unit is going as well added oil and then noticed the gauge goes to 0 after about five minutes of driving. Glad I checked this thread first before taking it to my mechanic since it sounds like an easy fix
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Old 04-14-2012, 09:45 PM   #20
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Mine is doing the same thing, 94 YJ 4.0L! I replaced the sending unit with a direct pressure guage and it still drops to 0 for a second and then rises to about 10psi. As I rev the engine it raises to about 25-30.

I'm not really sure what to do because every forum I look at says this is common, however they also say its the sending unit. I am not so sure the sending units are the issue here.

My 4.0 doesn't make a sound! No knocking or valve chatter! What do you guys think? Should I change the oil pump?
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Old 04-15-2012, 08:59 AM   #21
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bump!
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Old 04-15-2012, 11:07 AM   #22
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I would change the pump, and if that don't fix it, it is time for a rebuild.
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Old 04-15-2012, 01:01 PM   #23
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Where and how do you replace the sending unit? Any links to a write up or video?
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Old 04-15-2012, 01:33 PM   #24
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Quote:
Originally Posted by doolyd View Post
Where and how do you replace the sending unit? Any links to a write up or video?
Search here, there are HUNDREDS of threads on this.
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Old 04-16-2012, 07:42 AM   #25
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Sending unit is easy to change. Its located right at your oil filter with a wire connector on it. Just un-screw it and install the new one. I dumped a bottle of lucas in it and oil pressure is holding strong at 20psi now. I am going to ride it until it makes noise.

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