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Old 01-13-2007, 08:47 PM   #1 (permalink)
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4.0 oil pressure WTF

Long story short, I went wheelin a couple weeks ago and on my way back home my oil pressure dropped to nothing every time I came to idle at a stop light/sign and ran like crap. I had to rev it up to get any pressure at all which was still minimal. So next day I did a complete oil change and everything seemed fine. Drove about 15 miles to my buddy's house and I lost my oil pressure completely. Ended up getting to his house with the thing sounding like a diesel. So we swapped out the oil pump for a new one (screen was in perfect shape so re-used that) and started it up today. No oil pressure at all. I'm at a loss now as to what it could be. Any help is appreciated!
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Old 01-13-2007, 08:56 PM   #2 (permalink)
 
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well using a heavier oil could help for a temporary solution. oil pump does not create the pressure, how many miles are on your 4.0 ? could be worn main and rod bearings and crankshaft journals on a high mileage engine.

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Old 01-13-2007, 09:14 PM   #3 (permalink)
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Quote:
Originally Posted by billythefoo View Post
well using a heavier oil could help for a temporary solution. oil pump does not create the pressure, how many miles are on your 4.0 ? could be worn main and rod bearings and crankshaft journals on a high mileage engine.

It just turned 90,000 miles. It's a 2000 TJ by the way. I was hoping it wasn't something like that
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Old 01-13-2007, 09:16 PM   #4 (permalink)
 
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Here is the link to a site that i found for you to read up on i didnt read the entire thing but it sounds like he knows what hes talking about.

http://www.aa1car.com/library/us1097.htm
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Old 01-14-2007, 08:49 PM   #5 (permalink)
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Thanks for the link, thats a lot of useful info. Don't know if it really pertains to this problem or not though.

Today I decided to see if any oil was getting to the rocker arms. I started it up and had a buddy look for oil up there and nothing. The next thing we tried is taking the filter off (there wasnt much oil in there at all btw) and starting the engine up. If it were working correctly oil should have been spewing out of there, but nothing. Then we made sure the new pump was installed correctly, etc and it was. It looks like theres some kind of clog or something between where the oil pump is and the top end of the engine. We put a air hose where the filter goes trying to blow some air in there to free up anything but still nothing. Anyone know what the hell the problem could be?

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Old 01-14-2007, 09:21 PM   #6 (permalink)
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does it have internal or external relief valve? could be a broken relief valve spring
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Old 01-15-2007, 04:15 PM   #7 (permalink)
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stupid question, u did prime the pump in oil before u put it in right?? like put it in a bucket of oil and turn it till it spews oil? it wont move shit if you didnt. my pickup started leakin at about 150K miles, was doing much the same thing you describe. remember factory spec on these engines isnt much to start with, 13-17 psi i think.
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Old 01-15-2007, 04:58 PM   #8 (permalink)
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check where it runs off the distibutor, i cant say ive torn into the bottom end but i know that the new 4.0Ls had an issue with a crappy plastic drive wheel that ran the oil pump off the crank or distributor/cam position sensor.
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Old 01-15-2007, 09:24 PM   #9 (permalink)
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I did prime the new pump. Checked the crank bearings, checked the CPS and everything seemed fine. One thing that I did do that is baffling me now though is I pulled the oil pump out and blew some air up through there. Air came out of where the filter goes. Yesterday, I turned the engine over with no filter, and zero oil came out. I'm wondering if I unclogged something or what I might have done. Tomorrow I'm going to try to prime the engine by pulling out the CPS and using a drill with a long rod to turn the oil pump. See what happens then.
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Old 01-20-2007, 03:25 PM   #10 (permalink)
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Mine did the same thing a while ago....

oil pressure sensor was bad, put a new one in it and everything went back to normal.
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Old 01-20-2007, 03:37 PM   #11 (permalink)
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Really? That's a hell of a thing for a sensor to make happen. I'll def give that a shot though. I read that they are known for going bad but I just figured it would make the gauge read low.
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Old 01-20-2007, 04:03 PM   #12 (permalink)
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Yeah, from reading your first post it is exactly what happened. On mine I may have bumped and broke it while changing the oil filter...fragile little thing. Hope that solves your problem.
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