View Full Version : oil pressure
04-03-2010, 07:46 AM
Okay, So I was having oil pressure issues with my 96 ZJ, after getting warm the oil pressure would drop to almost zero and the light would come on. So I talked to a couple techs and they said it was the oil pump. So I go down to my buddies shop yesterday and tear the old one out and install the new one, quick and simple job right......NOT. So I get everything back together and go to flash it up and now I have no oil pressure at all, it's like the pump is not priming. Any thoughts would be greatly appreciated. Oh yea it is a 5.2ltr
04-03-2010, 01:01 PM
Did you prime the Oil pump when you put it in?.........how accessible is the oil pressure sending unit?....can you hookup an rfi to it?
04-03-2010, 01:27 PM
Hook up a mechanical oil pressure gauge and check actual pressure, maybe the sending unit.
04-03-2010, 01:39 PM
Had the same issue with my 4.9 after rebuild.....good pressure when cold near 0 when hot, replaced the pump which made no difference. Pulled the engine again and found that in my hurry to get the truck back on the road I had failed to notice the main bearings were std not the 10 under that I had ordered.......Had to have the crank turned and another new set of bearings. Been good ever since.
I've had other engines do the same as yours from excessive wear on the main or con-rod bearings. Never had a pump go on me yet.
04-03-2010, 02:00 PM
Put some 20/50 in it to see if anything changes that should help you diagnose it and make sure you prime the pump
04-03-2010, 03:43 PM
I am going to guess its a crank/ main bearing problem.
04-03-2010, 08:44 PM
did you prime the pump by hand before you installed it?
if not then it likely vacuum locked..
and your gonna have to tear it out and prime it by hand then reinstal
04-04-2010, 07:46 AM
Got it figured out. First the pump input busted upon first crank, second I didn't prime the pump. So took everything back off replaced the pump put everything back on and crank it over and imagine that 65 psi.
Back on the road now, gonna post a pic of it soon, got the wheels and tires on it now.
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