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Old 05-04-2006, 07:32 AM   #1
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no oil pressure

ok so this may be long

went to wellsville last weekend..
doing good following lil stock geo trackers and even a stock blazer
i go through the same holes they go through and what not
well one hole decided when i got out of it that it wanted to screw my oil pressure... as in the OP dropped to 0 when not hittn the gas

long story short.. changed oil 3 times that day
came home and today (wednesday) dropped oil pan.. it was perfetly clean..oil pump and screen CLEAN but i bought a new pump and put it on neways
filled it back full of oil...new filter
running GREEEEEEEEEAAAAAAAAT for bout 10-25 mins around 30psi
then all of a sudden the OP dropps to ZERO AGAIN!! and u can hear the lifter

now what the hell is the problem?
it is not smoking
it is not missing
the rods are not makn a noise
no leaks nothing

this is the 2nd time this has happened to me
last year i had this happen and we replaced motor

there was no sign of anything in the oil pan just oil

someone please help me

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Old 05-04-2006, 07:36 AM   #2
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I know this may sound kinda stupid...but have you thought about replacing the oil pressure sending unit?

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Old 05-04-2006, 08:32 AM   #3
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I put on a manual oil pressure guage before I changed the oil pump and at idle it read like maybe 1 or 2 PSI
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Old 05-04-2006, 08:57 AM   #4
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Wow! If you've done all that then I have no idea! Did you replace the oil pickup tube when you replaced the oil pump? I'm just throwing stuff out there. Sorry!
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Old 05-04-2006, 09:08 AM   #5
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i would like to know what is happening with this because mine started doing the same thing the other day. it runs just fine, but the oil pressure drops considerably when i'm not up in the RPM's. when i'm at speed it's fine. i've checked the oil i don't know how many times and there's always oil in it. i think i'm gonna replace the oil pressure switch. i'll let you know if that works or not. any other help would be greatly appreciated.
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Old 05-04-2006, 10:05 AM   #6
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You guys are talking about two different things here. Zero pressure vs low pressure.
Zero pressure is bad.

97TJAC,
What did the pump drive gear look like when you pulled it out? Was it badly worn, cracked, etc...?

my98tj,
My 2000TJ with 66k on it runs about 16lb of pressure at idle when fully warmed up. When the rpm's are 1500 or above I get 40 - 50lbs. It is my understanding that this is quite normal for the 4.0.
I have read that 10lb is the low limit so if you are at 10lb or above don't worry about it.
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Old 05-04-2006, 11:10 AM   #7
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I have the exact opposite poroblem. My guage is always pegged until my Jeep warms up. Then it goes down a bit. I am 99 percent sure that it is the sending unit. I just haven't gotten around to replacing it yet!
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Old 05-04-2006, 12:24 PM   #8
Knows a couple things...

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Early TJs, maybe late model TJs too but I am not sure, had bad oil pressure senders. They'd also often wait to send erroneous zero oil pressure signals until you were alone out in the boondocks near Midnight as happened to me!

Replacing mine completely stopped the multiple zero oil pressure indications, it's been ok the last 9 years.
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Old 05-04-2006, 01:28 PM   #9
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but i have the lifters ticking now

and i took an OP sending unit off another 4.0 Jeep and it did the same thing.. this was all before the ticking

the oil pumped looke fine...although some reason i was able to take it off with my fingers.. the bolts were loose and there was evidence of "blow by" on the gaskets


I am guessing this is the start of all my problems... bought the motor used at a junkyard and the damn pump wasnt on all the way

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