High Oil Pressure

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#1
I just bought time on a 2000 Jeep Cherokee Sport. The oil pressure gauge has been inconsistently reading high since I got the vehicle. I had some electrical issues and replaced the alternator. Now the electrical problems are fixed the high oil pressure reading is much more consistent and there is a lurching in the vehicle at regular operating speeds. I plan to simply change the oil today and reassess. If anyone has any helpful tips on how to correct the problem I would be much obliged. Thank You.
 
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#2
High and erratic oil pressure is probably your oil pressure sending unit, dash gauge, or highly unlikely your oil pump, in that order.

If you do not have a digital VOM, info, or ability to check out the sending unit and gauge, I would recommend replacing the sending unit. They are cheap and easy to install.

If you have a VOM and want to check it out, somebody in here will possibly walk you through the diagnostics.
 

kev2

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#3
this is the best vehicle design/made $.02
OK this is a 4.0L correct? great old school design.... never known for high oil pressure, just like the older V8s - under 10 at idle was common.

Now I would ask what is the gauge reading hot at idle? xpsi?

The sensor/sender is above yhe starter, a single wire GRY/YEL I would suspect it is grounded or open and sending a false reading... and would set DTC - p0522 or p0524... codes set?

Also for the drivability issue -
1) the Ck eng lite (CEL) confirm it comes on when you start and goes out in @3 seconds? yes no
2) is there any codes - post them
3) vehicle is STOCK - no modifications aftermarket parts? tell us
 
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#4
The alternator is the only aftermarket part I know of. The problem was present before I installed it though. The CEL comes on when I start the vehicle and goes out immediately. I haven't checked the codes. It's a 4. 0L, but it's not V8, it's straight 6. I drained some oil out of it earlier today and the problem went from constant back to intermittent. It still lurches on accelaration though. I haven't driven it to great extent, just around the neighborhood. I'm going to check the wire on the sensor. Thanks for the help.
 

kev2

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#5
Tell us what the oil pressure reading is ?
The CEL is operating GOOD news...can you determine if the lurching is ENG or TRANS (auto?) correct...
If automatic check fluid level- keep in mind jeep uses a SPECIAL trans fluid never the universal type..
Be aware some auto parts stores do free code checks- might help us ID a code that does NOT set MIL.

FYI: I was comparing the old school V8 with your I6, and the unuasual problem of HIGH oill pressure.
 

billr

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#6
What weight oil is in the engine, and when you "drained some", did you replenish, or was it over-full, or is it now running with a low oil level? High oil pressure almost never happens, either the pressure-relief valve is stuck closed (very rare) or the oil viscosity is way too high. I always suggest installing a mechanical gauge temporarily, right away, to verify pressure whenever there is a question about engine oil pressure; it's too critical to take any chance while checking things like senders and gauges.
 
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#7
Oil pressure sensor is generally located by the oil filter, when was the last time that was changed? Also limited by the pressure regulator. And is it a real pressure gauge? Or one of those closed with 2 psi of pressure in series with a fixed resistor. Is the oil pressure constant under all conditions, hot, cold, cruising speed or idle? If so, more than likely a fixed resistor in series with a switch and not a real pressure sensor.

GM pulls that, not sure about Chrysler.
 
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#8
If the gauge reads high with warm motor, at idle, it's probably the sending unit. A "stuck closed" pressure regulator would have no effect during those conditions....a properly working regulator would be in the closed position then.

If the gauge reads too high when a warm engine is revved, the regulator may be stuck, but if it is "jumping around" at a steady high RPM, the sending unit is the most likely culprit.
 

kev2

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#9
component location....

oops having trouble with sender picture - will try again
 
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#10
Both the 2.5 and 4.0L engines use this:



Its called an oil pressure switch, and it sure looks like a switch to me, the pressure sender is much larger as contains a diaphragm hooked up to a potentiometer.

Can't find the specs on it, but typically close at 2.5 PSI, gauge is not any different than the lamp that goes on or off, needle on guage goes to zero or some positive value depending on the size of the resistor in series with it. An ohmmeter across those two contacts would verify this. Either an open circuit if opened, zero ohms if closed.
 
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#11
The oil pressure sensor has a 3-wire electrical function very much like the Manifold Absolute Pressure (MAP) sensor. Meaning different pressures relate to different output voltages.
 

kev2

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#12
Danica you sure 3 wire? As I remember and my diagram shows 1wire - I posted color above GY/YL? having problems posting diagrams today - don't know why
 
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#13
Link to diagram...

http://repair.alldata.com/alldata/imagesWLinks?file=//imagebfl300e/11/52/27_cr00cherk_8w30-012.png&width=584&height=736&displayType=display&imgRotation=&links=

Link to webpage with multiple views, including pin configuration...

http://www.ebay.com/itm/Standard-Tru-Tech-PS317T-Oil-Pressure-Sender-or-Switch-For-Gauge-/160703448404?pt=Motors_Car_Truck_Parts_Accessories&fits=Year%3A2000%7CMake%3AJeep%7CModel%3ACherokee&hash=item256aac0554&vxp=mtr

Hey Nick...I am old enough to expect a oil pressure sender to be chunky enough to contain a rheostat, but I guess they found a cheaper way to do it.
 
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#14
Okay, so it is a real pressure transducer, kind of hinted by the 35 buck price tag I noticed. Only two vehicles I own with real pressure transducers is my P-30 motorhome and 88 Supra. They both show high pressures when cold and drop down at idle. Yes, National Semiconductor and now others have integrated a pressure transducer into a single tiny chip.

Do have a real oil pressure gauge with a number of different fittings to replace that transducer to test the actual oil pressure just for testing. The original transducer should show about the same. That way you know for sure whether its your transducer or if you actually have engine oil problems.

Back in the mid 30's to about the mid 50's they were using real pressure gauges with an 1/8" copper tube to the engine, if that leaked or the diaphragm leaked, would get hot oil on your pants. Then came that switch with a lamp that was nothing short of a joke. Have on of those on my new Cruze, but least added a low oil level sensor. On the 1910 Buick with overhead valves, no valve cover, every half hour or so, had to stop and hand oil the valve train.
 
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#15
The folks at the Express Oil Change tell me high oil pressure's a good thing; it's an example of a strong engine. I believe the lurching is caused by a failing fuel pump. Anybody know if a salvage part is alright for this fix or should I purchase a new part? Fella at Express said he thinks there's a faulty ground in the fuel pump system for this make and model. I'm gonna try and take it easy gettin back and forth to work and out to our new place till I get the time and the part. Probably be a couple days. I'm gonna grab an oil sensor at the salvage yard and change that out as well.