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Oil pressure drop when stopped


Scout425

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Nov 22, 2018
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As the title suggests, today my oil pressure has been plummeting when stopped. As soon as I take off it returns to normal. Placed the Jeep in neutral while moving and the pressure remains normal. Searching this forum did not turn up and threads on this issue. Has anyone run into this issue and resolved it?

2006 LJ ~ 145,000miles
4.0L
NSG370
 

CodaMan

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also, the oil pressure sending units have been know to fail. You could always try replacing it.
 
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Scout425

Scout425

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I guess I should have clarified a bit. The pressure falls enough to set off my check gauges light. Ill look into the oil sending unit.

After letting the engine cool down I let it idle for 10 minutes with no issues. I also have not been able to replicate the fault.
 

Andrew Mac

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Experienced the same issue around 150000 miles. Replaced the sender (switch). Problem went away. I did confirm that it was not a pump issue by checking with a calibrated pressure gauge prior to replacement. Pressure was good.
I will also suggest spending the extra money for the factory Mopar switch. Avoid the knock off's. There is a difference.
 

bromel

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You have a late-model TJ, so it has a dummy oil pressure gauge. It will always read around 40 psi unless something is wrong. The oil pressure sending units are notoriously finicky, so that is almost certainly your problem. Replace with mopar, not aftermarket.
 

Jerry Bransford

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You have a late-model TJ, so it has a dummy oil pressure gauge. It will always read around 40 psi unless something is wrong.
It's definitely not a dummy gauge, it's just programmed in such a way that some think it is. The programming is that the computer looks at the real pressure coming off the sender and if it's within acceptable limits it moves the pointer to mid-scale, or about 40 psi. It drops or raises if the true underlying pressure is below or above the acceptable limits.

Why did Jeep do that? Because with the introduction of the '97 TJ, sales took off and people started buying them who had never had a vehicle with an oil pressure gauge. They saw the oil pressure going up & down as a problem and many of them complained to the dealers who were not always successful in convincing them it was normal and how it is supposed to be. Dealers were complaining to Jeep who then reprogrammed it as it is now to stop the complaints.
 
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texvet

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Figured I would add to this thread as I had the exact same issue hit my LJ today after a run out to the shooting range. Almost crapped my pants when the red check gauges light came on and I saw my oil pressure at zero when I rolled up to a stop at a stop light.. Exact same scenario, pulled into parking lot, checked oil level to make sure I missed something like a giant oil cloud behind me as I burned off all my oil via a leak while driving down the highway, got in started up, O.P. back at normal operating level, then pulled out of parking lot, came to a stop and pressure dropped to zero with check gauge lights. revved engine a little light went off O.P. back to normal. Several more stop lights on the way home without any repeat of the zero O.P. I currently have 83,555 on the clock.

Ordered MOPAR part # 5149097AA (replacement for 4868672AA) today and will install later this week. I'll report back after the install and few days of driving to see if the issue returns for anyone in the future that has this type issue.
 

Jerry Bransford

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Figured I would add to this thread as I had the exact same issue hit my LJ today after a run out to the shooting range. Almost crapped my pants when the red check gauges light came on and I saw my oil pressure at zero when I rolled up to a stop at a stop light.. Exact same scenario, pulled into parking lot, checked oil level to make sure I missed something like a giant oil cloud behind me as I burned off all my oil via a leak while driving down the highway, got in started up, O.P. back at normal operating level, then pulled out of parking lot, came to a stop and pressure dropped to zero with check gauge lights. revved engine a little light went off O.P. back to normal. Several more stop lights on the way home without any repeat of the zero O.P. I currently have 83,555 on the clock.

Ordered MOPAR part # 5149097AA (replacement for 4868672AA) today and will install later this week. I'll report back after the install and few days of driving to see if the issue returns for anyone in the future that has this type issue.
Good decision, that is what fixed mine. My red Check Gauges light went on and alerted me to the 0 oil pressure on my then-new '97 TJ's oil pressure gauge and it freaked me out since I was way out in the middle of the desert on a dark deserted road with no town within 10-15 miles of me. It was right after that when I discovered faulty oil pressure sensors are common.
 

tnpete

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Watch removing the old one. Mine snapped the elbow going into the block. That 10 minute job, turned into 2 hours +. But on the bright side, I did go ahead and change out the 3 piece motor mount on the pass side. :rolleyes: Also local Napa had the elbow. Put a left handed drill bit into the part left in the block. And it screwed out easy as could be.
 

Bootheel Boy

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My 2005 had an issue years ago where randomly it wouldn’t show oil pressure at startup. I could shut it off and restart it and everything would be fine. New Mopar oil sending unit fixed the issue.
 

texvet

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Replaced the oil pressure sending unit and was trouble free until after a two hour drive today. Pulled up a stop light after an hour of freeway driving and I was met with the 0 oil pressure, check engine, and audible alarm. slight rev of the motor from neutral and pressure back to normal with no more issues on the way home. As of today I'm thinking either possible harness issue or I received a bad part; not the first time something like that has happened to me.

@Jerry Bransford is there a way to bypass the electronics on the sending unit to not throw the check engine? Thinking about wiring up a temp mechanical gauge into the dash to monitor for a few days to be on the safe side.
 

ItchyDong

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Sounds like you could have an intermittent short in the signal wire. The higher the pressure, the higher resistance in the sending unit. If you short the signal to ground, there's zero resistance, or zero pressure according to the PCM. I'd backprobe the signal wire and go to battery ground with a multimeter set to beep with continuity while I wiggled the harness.
 
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Goatman

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Have you checked your oil? Is it full? Smells gassy? Does the engine start to make any knocking sounds when displaying no pressure? Because with no oil pressure the hydraulic lifters will start to deflate and make noise. If none of these issues are happening you can be confident it's just the gauge or sending unit.
 
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Scout425

Scout425

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In my case, oil is good. Just went through a thorough tune up a few weeks before this symptom started.

I do not get a change in sound when the pressure drops. Only the gauge flatlining and warning buzzer.

I have not attempted to resolve the issue yet. Simply started keeping the revs close to 1000-1200 to keep the buzzer from going off. Next week Im going to pick up a new OEM sending unit. Gotta get ready for the drive to TN to pick up Bulldawgs new LJ hardtop.
 

John Scoggins

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Had the same issue, ended up that cleaning the two connections behind the instrument cluster and the center connection on the PCM cleared up the problem.

I did change the sending unit with a Mopar one prior to cleaning but had same problem until cleaning.
 
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Assforkr

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Good decision, that is what fixed mine. My red Check Gauges light went on and alerted me to the 0 oil pressure on my then-new '97 TJ's oil pressure gauge and it freaked me out since I was way out in the middle of the desert on a dark deserted road with no town within 10-15 miles of me. It was right after that when I discovered faulty oil pressure sensors are common.
Jerry, I know this seems like a fool's errand but are you aware of any way to bypass the factory controls and have the gauge read the actual pressure?
 

Jerry Bransford

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Jerry, I know this seems like a fool's errand but are you aware of any way to bypass the factory controls and have the gauge read the actual pressure?
Not that I'm aware of. I'd like that too. Though I'm comfortable with it as is, it only reads mid-scale if the underlying oil pressure is ok.