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?

Oil sending unit is bad. usually by the oil filter.

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.

Check the type of oil you are using as it clogs the pin in the oil poressure sender unit.

check the oil descending unit or ur oil pump might b clogged up with soot, just some advice hope it works

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.

If you got the same oil pressure reading with the new and old sending unit, more then likely your oil pump pick up tube is clog up, remove oil pan and clean or replace pick up tube also replace pan gasket.Goodluck.

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.

the first i would do is to see if the oil sending unit is ok and if you gage is working right and if they are then checkout the oil pump.

how many miles are on the vehicle this usually happens when the oi; pump or engine is wore out.

The most common problem is a bad oil pressure switch on the 99-02 grand cherokee with the 4.7l v8. The part has failed on 90% of all 99-02 grand cherokees I have worked on. The housing is junk,but since it has lasted longer then 36,000 miles the factory would not issue a recall. The oil pressure switch can be purchased at any outlet. but have found the duralast was decent. that being said Go to autozone and get part # PS471 (oil pressure switch for 1999-2002 N code 4.7L V8.) chances are if you encounter the same problem after replacement you will need to drop the oil pan and un clog the oil sump.

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.