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Unread 04-27-2013, 09:17 PM   #1
TheFryer
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96 XJ 4L 4x4 oil pressure issue

ok to start off i had a slight bottom end knock, so i replaced the rod bearing's. now i still have a light knock when cold only. as soon as the temp moves the knock is gone. running 10-30w castrol gtx high millage as i have 197k miles. i did a decent trip on the HWY this week and i have noticed the cold knocking sound is gone. how ever my oil pressure is no longer steady.

normally ran 30-40 cold, 50-60 hot, and was steady with the rpm. now is it 40-50 idle and 40-65 hot, but not steady, it bounces around bad. i am using an aftermarket oil psi Gage, and have replaced it because i thought it might have had an issue, new fittings, lines and everything, even made sure there are no kinks in the plastic tube.

Any idea's? i did notice when i did the rod bearings they was very worn, to the copper so i went .001 over stock. and the timing chain has almost 1/2" of play turning the motor one way then the opposite.

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Unread 04-28-2013, 08:13 AM   #2
CJ7-Tim
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If the knock goes away, I wouldn't worry, especially at 197K miles. If necessary find a good used 4.0.

Your oil pressure should greater than 13 psi at warm idle and 30-60 psi at 60 mph. 35-45 psi at 60 mph is typical for any of the 6 XJ's I have owned. Cold oil pressure doesn't really mean anything.
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Unread 04-28-2013, 09:24 AM   #3
M35A2
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You should have used plastigauge on the bearings. Just because the old bearings were into the copper doesn't mean the crank was worn and needed an oversize set.
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Unread 04-28-2013, 02:49 PM   #4
TheFryer
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i went 1 thousandth over. on a motor with 197k i figured it wouldn't hurt. if anything prolong me to save up for a full stroke out. she still have a ton of power and no issues hitting the rev limiter when i play around on the road/ dirt/mud. i have been taking it easy on her though as i want to get another block and build it so all i have to do is a swap out.
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Unread 04-28-2013, 07:17 PM   #5
AZ Jeff
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Just to be sure===you are not mistaking piston slap for rod knock, are you? Piston slap tends to go away on a warm engine.....
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Unread 04-29-2013, 08:54 AM   #6
TheFryer
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hmmm that could be it AZ Jeff. i am not sure how to check that without pulling the head off though. the motor has the normal lifter tap, but the cold knock sounds like it is from the lower to mid block so it is possible. any way to find out without pulling the head? i would just prefer not to sense i am trying to save to make a stoker to replace it.
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Unread 04-29-2013, 07:35 PM   #7
BIGBADWOLF
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Quote:
Originally Posted by M35A2 View Post
You should have used plastigauge on the bearings. Just because the old bearings were into the copper doesn't mean the crank was worn and needed an oversize set.
ABSOLUTELY Going .001 over without measuring could be catastrophic.
You have to have enough clearance for the journal to lube. A fluctuating oil pressure is a good sign that the bearing are too tight.
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Unread 04-29-2013, 09:29 PM   #8
Cmense
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Sorry to jack the thread but if oil pressure is low at idle when warmed up and only around 40 at 65mph is that bad? It sits at the first hash after 0psi when at idle. My guess is faulty sending unit?
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Unread 05-04-2013, 07:59 AM   #9
TheFryer
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honestly i do not trust the factory sending units. i had bought 2 from having odd issues with reading's in the first 4 years i had the jeep. then i went to an after market mechanical, i like to know actual numbers, not lines. i also have an aftermarket A/F ratio, engine temp, trans temp gauge. when i change motors i will also be adding a voltage and boost gauge. but that's because of my stereo system draw and i will be running a turbo on the new motor for a little added fun. how ever if you do go with aftermarket gauges make sure to keep the factory sensor's hooked up and working. if not it can tell the computer odd things and it will not run right or get horrid gas millage.
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Unread 05-04-2013, 08:32 AM   #10
CJ7-Tim
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Quote:
Originally Posted by Cmense View Post
Sorry to jack the thread but if oil pressure is low at idle when warmed up and only around 40 at 65mph is that bad? It sits at the first hash after 0psi when at idle. My guess is faulty sending unit?
Your oil pressure should greater than 13 psi at warm idle and 30-60 psi at 60 mph.

35-45 psi at 60 mph is typical for any of the 6 XJ's I have owned.
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Unread 05-04-2013, 10:52 AM   #11
Cmense
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Quote:
Originally Posted by CJ7-Tim View Post

Your oil pressure should greater than 13 psi at warm idle and 30-60 psi at 60 mph.

35-45 psi at 60 mph is typical for any of the 6 XJ's I have owned.
Thanks for clearing that up
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Unread 05-04-2013, 12:00 PM   #12
BIGBADWOLF
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Originally Posted by Cmense View Post
Thanks for clearing that up
Yeah but that does not mean your motor will grenade if it is lower. 5psi at idle is freaky but it is enough.
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