Oil pressure issue.

[Immortal]

On a 1999 Grand Cherokee Limited with the 4.7L V8.
Oil pressure drops off to 0 when the oil has warmed up. First happened when my wife was driving to work. Towed it home, checked oil. Lots of oil, doesn't smell burnt. Started up the truck, oil pressure was good for about 10 seconds, then dropped like a rock.

Any thoughts?

[Gearhead]

Likely the Sending unit , I like to connect a real pressure guage on a hose to the port where the sendingunit threads into the block to confirm a bad sender.

[Immortal]

k...
guess I had better buy a Haynes manual to find that port.

TY!

[WhiteOut]

Hey Trevor, you can borrow mine if you want.

[Bnine]

Hopefully its the sender but I doubt it. Bad sender should be more erratic, or just not work at all.

I have had this issue with a 4.7 before. The rod bearings were. Its a pretty light bottom end in those motors.
If the mechanical gauge has the same problem, you will need to drop the pan and start checking bearings. The furthest to the rear are always the worst, so start there.

If there is sludge or scale in the pan, that is another hint the bearings have been beat out due to oil starvation.

Lastly, the sender will drop to 0 with any pressure below 10 lbs. You may still have some pressure.

[msakatch]

i have a dodge 1500, with the 318, started out similarly with the drop in oil pressure when warmed up, and then eventually became erratic, it was the sending unit, about 50 bucks from the dealership, put it in, good as new. I was worried it was not the sending unit and something wrong with the oil pump, or with a buildup of sludge like oil in the oil pan, or something wrong with the oil pan, but thankfully it was just the sending unit, and its all fixed, probably the cheapest fix i have ever had on my truck to date

[Immortal]

UPDATE!!!!

Oh, my LORD!
What started out as an oil pressure issue just kept on escalating. The guage was not reading oil pressure, but lots of oil in the pan, so I parked the WJ until I had time, and a garage to look into it (wifey drove the 99 XJ in the meantime). The WJ sat for a week and a half (during the lovely -30 weather). Finally convinced the wife that IF she wanted her baby back, I would HAVE to get it into the warm garage to work on it. Go out, start up the beast. Trouble starting.... then a REALLY rough idle. Put into drive... didn't even feel like the transmission loaded up. Touched the throttle (didn't stomp on it, as I was still unsure if there was any oil being pumped through the system)..... nada. RPMs didn't go up... in fact it sounded like it was going to stall. Pushed the WJ into the garage. Let it warm up. As per a mechanic on this site, I pulled the plug on the Oil Pressure Sending Unit. Some oil was present on the inside of the plug, indicating that the OPSU was shot. Replaced OPSU and oil filter (hella easy to get at the sending unit with it out of the way, with a 1 ¹/₁₆" deep socket).

Now, to tackle the rough idle/no want to drive issue. Thankfully the mechanic neighbour brought home a scanner. "Crankshaft Position Sensor Faulty" is what it told us. Tested the CKPS while rotating the engine. Nada. Removed CKPS, rotate engine while feeling for crank movement. Crank was turning (ffwew!!). Replaced stupid sensor. Reassembled everything. Replaced battery, as it no longer wanted to hold a charge. Crossed fingers, held tongue in correct position, turned key. VROOOOOM!!!! It now has oil pressure on guage, and drives. What a fiasco. I am soooooo thankful that this was not a larger problem, and was relatively easy, and cheap to fix.
Parts from Chrysler were approx. $5 each more expensive than from AutoValue. I like to go OEM with sensors.

Cheers, and thanks for everyone's input. 

[sylvrinvader]

so your story goes like      :'( :'( :'(     and now the wife  you  . aww how sweet

[Immortal]

more like
  :'( :'( :'(
 
 
 

[FiEND]

we all love "happy ending"

[Bnine]

Awesome, congrats on the simple fixes.

[hps4evr]

hehehehe... glad to hear you came out with the big "W" in the end.

next time i charge for my cheap advice;)