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Unread 12-16-2006, 09:31 PM   #1
Kornik
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Oil pump replacement in 4.0 - any hints?

Hi guys!

Today, on my way to the movies I've notices that my oil pressure dropped down to 20psi when idling. And the engine started to make some sound, which (forgive me my English) I would call chirping. Like I have small bird in the engine, somewhere in the middle (between 3rd and 4th cylinder) definitely on the right side.

As the pressure wasn't to high before (around 38psi when hot comparing to my XJ's 42 at hot) I suspect that my oil pump is dying.

Now:
a) Is my diagnose right? or is there something else going bad in those engines?

b) Is there anything I should be aware of before I'll take the old one out? Anything to check while I have oil pan down?

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92 XJ Laredo Mods: bored TB, 3" lift, 1-ton steering
93 ZJ Limited Mods: bored TB, K&N insert, e-fan; prothane bushings, NP242J, 3" lift, 1-ton steering; Atlas winch
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Unread 12-16-2006, 09:52 PM   #2
JFM626
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Don't rely on the electrical gauge to be accurate. Use a mechanical one to be sure before tearing into your engine.
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Unread 12-16-2006, 10:00 PM   #3
-Joe-
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20 psi isnt low..

I believe something like down to 13 is supposed to be normal..
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Unread 12-16-2006, 10:06 PM   #4
Kornik
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Quote:
Originally Posted by JFM626
Don't rely on the electrical gauge to be accurate. Use a mechanical one to be sure before tearing into your engine.
Of course I will, but what about the sound? To me it's like a shaft turning without lubrication in it's bearing.
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92 XJ Laredo Mods: bored TB, 3" lift, 1-ton steering
93 ZJ Limited Mods: bored TB, K&N insert, e-fan; prothane bushings, NP242J, 3" lift, 1-ton steering; Atlas winch
Some ZJ parts for sale
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Unread 12-16-2006, 10:10 PM   #5
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Quote:
Originally Posted by -Joe-
20 psi isnt low..
I believe something like down to 13 is supposed to be normal..
For me anything above and below 40 psi is not normal - that's why the pressure relief valve is there. I accept up to 50 psi when it's 15 degrees outside. But after it's warmed up it should stay level no matter what. And I know it can, as I have XJ with same engine and similar millage and there the pressure is staying on 42 all the time no matter if I have 650 or 3000 RPMs.
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92 XJ Laredo Mods: bored TB, 3" lift, 1-ton steering
93 ZJ Limited Mods: bored TB, K&N insert, e-fan; prothane bushings, NP242J, 3" lift, 1-ton steering; Atlas winch
Some ZJ parts for sale
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Unread 12-16-2006, 10:18 PM   #6
-Joe-
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Quote:
Originally Posted by Kornik
For me anything above and below 40 psi is not normal - that's why the pressure relief valve is there. I accept up to 50 psi when it's 15 degrees outside. But after it's warmed up it should stay level no matter what. And I know it can, as I have XJ with same engine and similar millage and there the pressure is staying on 42 all the time no matter if I have 650 or 3000 RPMs.
Im just stating what the manual says..

Mine has always changed according to temp and speed. ITs never been steady.
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'95 Jeep Grand Cherokee Laredo I6 4.0L
242TC - Extreme Engineering 2" Front Lift/1.75" Rear Lift - ES9000 Shocks + JKS BPEs
Moog Cargo Control Springs
Magnaflow Converter - Dynomax Muffler
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Unread 12-16-2006, 10:24 PM   #7
Kornik
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Quote:
Originally Posted by -Joe-
Im just stating what the manual says..
Mine has always changed according to temp and speed. ITs never been steady.
So maybe I'm overreacting, but
a) as I said before it's staying level in my XJ after warm up on 42psi,

b) next Monday I'm going to make some 2000 miles trip to Colorado, and I would love to make it safely back and make it in my ZJ. If I won't be sure about it's being reliable enough I'll be forced to take XJ and it's something my wife won't like.
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92 XJ Laredo Mods: bored TB, 3" lift, 1-ton steering
93 ZJ Limited Mods: bored TB, K&N insert, e-fan; prothane bushings, NP242J, 3" lift, 1-ton steering; Atlas winch
Some ZJ parts for sale
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Unread 12-16-2006, 10:37 PM   #8
-Joe-
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Not about the noise.. I would be concerned.. But my 4.0 is loud anyways.

I changed my oil pump due to a noise i thought was it.. My pressure still remained the same with the new pump, its just never been steady. Could be my worn engine though.
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'95 Jeep Grand Cherokee Laredo I6 4.0L
242TC - Extreme Engineering 2" Front Lift/1.75" Rear Lift - ES9000 Shocks + JKS BPEs
Moog Cargo Control Springs
Magnaflow Converter - Dynomax Muffler
235/75/15 AT Uniroyal Liberator Tires
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Unread 12-16-2006, 11:24 PM   #9
anticrombie
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Oil pressure shouldn't stay the same. It fluctuates with the RPM's of the engine.
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Unread 12-17-2006, 05:47 AM   #10
greasefingers
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Basically the oil pressure gage tells you that the oil pump is working. That’s about it! The gage is not necessary to have. That is why most vehicles don’t have them. If however you notice that the gage is reading different than normal, then I would replace the filter, no matter how old it is, and then I would have a good look at the sending unit (transducer). They are known to act up. Unplug the electrical connector and inspect it for oil leaking into the connector. I would replace the transducer first before replacing the oil pump.

From the FSM: For the model years (1993 to 1996) 4.0L engine: the oil pressure at 600 rpm should be around 13 psi. At 1600 rpm and higher the pressure should be between (37 – 75psi)

So Anticrombie is very correct. Oil pressure is directly proportional to rpms. Temperature and viscosity will have a minor effect on it as well.

The only time I heard a bird chirping in the engine bay area, was when my friends Jeep had a bad distributor bearing!
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Unread 12-17-2006, 08:09 AM   #11
Katesdad
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Distributor bearing would be easy to check, just remove cap and rotor and see if there is any play in the shaft. One thing that helps alot is using a long screwdriver as a stethescope <-- not spelled right? You can zero in on the sounds inside the engine. My two chirping noises have come from the A/C compressor clutch and the idler pulley. Oil shavings will show up pretty quick in the oil if its a bad bearing within the engine. Just keep a close eye and ear on it and change the oil soon.

My oil pressure is all over the place too.
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Unread 12-17-2006, 08:21 AM   #12
SnaFu2
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Quote:
Originally Posted by Kornik
Hi guys!

Today, on my way to the movies I've notices that my oil pressure dropped down to 20psi when idling. And the engine started to make some sound, which (forgive me my English) I would call chirping. Like I have small bird in the engine, somewhere in the middle (between 3rd and 4th cylinder) definitely on the right side.

As the pressure wasn't to high before (around 38psi when hot comparing to my XJ's 42 at hot) I suspect that my oil pump is dying.

Now:
a) Is my diagnose right? or is there something else going bad in those engines?

b) Is there anything I should be aware of before I'll take the old one out? Anything to check while I have oil pan down?
OIL PUMP PRESSURE
The MINIMUM oil pump pressure is 89.6 kPa (13
psi) at 600 rpm. The MAXIMUM oil pump pressure
is 517 kPa (75 psi) at 1600 rpm or more.

The above was taken from the '97 FSM.
Didn't see anything about a "chirp" though.
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Unread 12-17-2006, 09:11 AM   #13
Kornik
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Quote:
Originally Posted by greasefingers
The only time I heard a bird chirping in the engine bay area, was when my friends Jeep had a bad distributor bearing!
OK maybe I'm a little bit overreacting, but I don't believe in coincidences and that sound showed up exactly at the moment the pressure gauge started to behave as I said. Before that readings were steady around 38-40 psi almost like in my XJ. That's why I'm suspecting oil pump. Anyway, I'll closely examine everything today before I'll tear down oil pan and pump. I'll drain oil and will look for metal in it. I think I will even drop down the serpentine belt and examine idle puller - as you suggested.
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92 XJ Laredo Mods: bored TB, 3" lift, 1-ton steering
93 ZJ Limited Mods: bored TB, K&N insert, e-fan; prothane bushings, NP242J, 3" lift, 1-ton steering; Atlas winch
Some ZJ parts for sale
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Unread 12-17-2006, 10:01 AM   #14
Kornik
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Quote:
Originally Posted by greasefingers
The only time I heard a bird chirping in the engine bay area, was when my friends Jeep had a bad distributor bearing!
That will be easy to check, I will swap them between my XJ and ZJ and see if the sound goes ofter :-)
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92 XJ Laredo Mods: bored TB, 3" lift, 1-ton steering
93 ZJ Limited Mods: bored TB, K&N insert, e-fan; prothane bushings, NP242J, 3" lift, 1-ton steering; Atlas winch
Some ZJ parts for sale
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Unread 12-17-2006, 04:03 PM   #15
Kornik
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Quote:
Originally Posted by greasefingers
The only time I heard a bird chirping in the engine bay area, was when my friends Jeep had a bad distributor bearing!
That's why I love this forum - I swapped distributors with my XJ (actually I just put the XJ's one in the ZJ) and sound stopped! Now I have to find new distributor for my XJ :-)

As for now I will leave the oil pump intact closely observing how it behave in near future.

Thanks again!
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92 XJ Laredo Mods: bored TB, 3" lift, 1-ton steering
93 ZJ Limited Mods: bored TB, K&N insert, e-fan; prothane bushings, NP242J, 3" lift, 1-ton steering; Atlas winch
Some ZJ parts for sale
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