Question about 1999 Jeep Grand Cherokee

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99 jeep grand cherokee 4.7 v8 oil pressure drops from 40 at idle to 0 when given rpms. Will come right back to 40 when you let idle again. I have removed pan and checked screen. It was clean. Original sending unit was leaking so I replaced. Still thew same. I hooked up aftermarket gauge and pressure never goes below 40 no matter what. Hook back up sender and it acts up again. Don't think 2 senders would be bad. Could it be oil in plug in missing up current?

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  • wrench31 Jan 16, 2010

    Installed another insturment cluster. Same problem. I have an electrical problem,but haven't found it.Thanks

  • Stan Ford Jan 22, 2019

    The gauge is faulty or there is a fault in the electric circuit from the sender unit to the oil gauge.

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Oil gauge may be bad, you said you changed the oil sending unit, and tried a aftermarket which worked, so the other option is to have you oil gauge checked. The sending unit may be good but you gauge is not reading proper.

Posted on Jan 12, 2010

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1 Answer

99 jeep grand cherokee 4.7 v8 oil pressure drops from 40 at idle to 0 when given rpms. Will come right back to 40 when you let idle again. I have removed pan and checked screen. It was clean. Original...


From what you just said, it sounds like the problem may be the dash gauge itself. I have only seen one oil pump act like that (mine) .... in that case the pump drive gear was turning on the shaft and slowing down as rpm increased but that is so rare as to be a non issue, especially when the mechanical gauge reads fine. I'd either replace the dash gauge or just install the mechanical gauge permanently on the dash. Doubt if oil in the plug will do that but you can check the plug, clean it and check the integrity of the wires going into it just to be sure.

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I have a 99 Jeep Grand Cherokee 4.7 oil pressure reads 40 at idle and drops to 0 when given rpms. Pull pan screen was clean. Noticed oil sending unit was leaking, I replaced it. I still have the same...


I just had the same problem with a malfunctioning gauge with a very oily sending unit. I went to Oreilly's auto and got a replacement sending unit for $38 and put it in and got the same results you did. I would have 40 psi at idle and it would drop to zero and throw the check gauges light when giving it throttle. I found some posts online that stated to only use official mopar sending units in these vehicles so I gave that a try. Problem solved!!! I now have 45-50 psi at idle and it climbs slightly when under throttle. The sending unit from Chrysler is around $52.

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Oil gauge fluctuates back and forth. sometimes


You'll need to determine if the oil pressure is actually changing, or if the sending unit or gauge is lying to you. Be certain the oil level is up to normal, then check the actual oil pressure with a test gauge. If the pressure varies (drops) at engine idle, perhaps your pressure bypass is defective, or perhaps the oil pump is worn. Testing with a known good pressure gauge should lead you in the right direction.

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To replace the switch, under the hood look for the power steering pump on the driver side of the vehicle, to the right and under the p/s pump is the oil pressure switch, If it is wet, its bad for sure, remember to disconnect the battery before service,as not to harm the gauges.

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