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Old 10-27-2010, 12:40 PM   #1
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"low oil pressure in the cylinders?"

Just got word back from the stealership about my fiance's TJ.

According to the guy I talked to we've got "a serious issue."

The oil pressure gauge doesn't always work, so they put their "machine" (whatever that means) on the truck and it told them the motor has low oil pressure in the cylinders. I know there isn't oil in the cylinders, so he must be confusing something, but I don't like hearing "low oil pressure."

Factory specs are suppose to read a minimum of 13 psi of oil pressure from where ever the "cylinders" are located. The TJ is running 8 psi.

It could be something like an oil pump pickup, or even the pump itself. The service writer (i assume that was his job title) said that at very worst the bearings could be going bad which would require a total motor rebuild.

The motor doesn't tick, it sounds and runs healthy, save the ONE time it misfired for a few miles. I know what a bad motor sounds like, and this TJ sounds nothing like a bad motor.

Currently I'm not 100% sure what my next few moves should be. I know the factory oil pressure gauge setup is garbage in comarison to other options, so I think my first move is going to be the purchase and install of a mechanical gauge.

Does anyone have any other suggestions? This Jeep is ours for life, so trading up isn't gonna happen.

Can I diagnose a bad oil pump somehow? Is there something else I should look into?

Thanks in advance for the help!

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Old 10-27-2010, 12:48 PM   #2
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Before you do anything else, and I'm assuming you've checked your oil level, install a new oil pressure gauge sending unit. That might be the only thing wrong.

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Old 10-27-2010, 12:53 PM   #3
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Originally Posted by hellhound94 View Post
Before you do anything else, and I'm assuming you've checked your oil level, install a new oil pressure gauge sending unit. That might be the only thing wrong.
You assume correctly, sir, oil level is indeed correct.

I don't wanna use the factory setup. Its weak and known to be problematic. I'd rather go with a mechanical setup and ditch the factory gauge alltogehter.
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Old 10-27-2010, 01:10 PM   #4
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Oil pressure sending unit is well known to fail on our Jeeps. I bet that is bad and nothing else is wrong with the engine.

And the guy who told you there is low oil pressure in cylinders doesn't know ANYTHING! DO NOT go back to that dealership to get anything fixed!

You can go to mechanical gauge route but make sure you set it up properly (no kinks in the line or air .. etc).
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Old 10-27-2010, 01:35 PM   #5
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Originally Posted by banipal19 View Post
Oil pressure sending unit is well known to fail on our Jeeps. I bet that is bad and nothing else is wrong with the engine.

And the guy who told you there is low oil pressure in cylinders doesn't know ANYTHING! DO NOT go back to that dealership to get anything fixed!

You can go to mechanical gauge route but make sure you set it up properly (no kinks in the line or air .. etc).
Yeah, I have no idea where he got the "cylinder" thing. But in his defense he was just a service writer, not a tech, so he probably just misspoke.

I'm hoping to find a gauge with a metal line instead of plastic, but if I can't I'll also need to make sure the line never gets hot and melts.

Does anyone have experience removing/deleting factory oil pressure gauge? I'd like to have the "Check Gauges" light gone for good, unless it really needs to be on.
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Old 10-27-2010, 01:45 PM   #6
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You didn't tell us anything about the Jeep. Year, miles, 2.5 or 4.0 ?

Generally speaking, a dealer telling you you've got a "serious issue" is no big deal.
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Old 10-27-2010, 01:47 PM   #7
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Electric units are accurate when they are working properly. So I just replaced mine instead of messing around with all electrical components/wires to stop "Check Gauges" light and running a line for mechanical gauge. It's not that expensive to replace it and take about 5 minutes to do it. I wouldn't mind doing it again.
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Old 10-27-2010, 02:58 PM   #8
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Quote:
Originally Posted by Gee oh Dee View Post
Just got word back from the stealership about my fiance's TJ.

According to the guy I talked to we've got "a serious issue."

The oil pressure gauge doesn't always work, so they put their "machine" (whatever that means) on the truck and it told them the motor has low oil pressure in the cylinders. I know there isn't oil in the cylinders, so he must be confusing something, but I don't like hearing "low oil pressure."

Factory specs are suppose to read a minimum of 13 psi of oil pressure from where ever the "cylinders" are located. The TJ is running 8 psi.

It could be something like an oil pump pickup, or even the pump itself. The service writer (i assume that was his job title) said that at very worst the bearings could be going bad which would require a total motor rebuild.

The motor doesn't tick, it sounds and runs healthy, save the ONE time it misfired for a few miles. I know what a bad motor sounds like, and this TJ sounds nothing like a bad motor.

Currently I'm not 100% sure what my next few moves should be. I know the factory oil pressure gauge setup is garbage in comarison to other options, so I think my first move is going to be the purchase and install of a mechanical gauge.

Does anyone have any other suggestions? This Jeep is ours for life, so trading up isn't gonna happen.

Can I diagnose a bad oil pump somehow? Is there something else I should look into?

Thanks in advance for the help!
a mechanical gauge will tell you if the pump is bad
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Old 10-27-2010, 04:31 PM   #9
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Can I have good oil pressure at the gauge but have BAD oil pressure elsewhere?
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Old 10-27-2010, 04:50 PM   #10
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I have the same issue I have replaced the oil pump and dropped and replaced all the Rod bearings no help. using a calibrated oil pressure gauge that I tapped in line I run 5-8 lbs once it is warm at idle and 19-22 at 1700rpms (with Lucas oil treatment) heres the kicker the cluster oil gauge reads 3/4 over all the time this is because the ECM sees oil pressure its more of a guide I guess but the mechanical gauge tells the real story the engine sounds fine I have researched a little and believe it is the Cam bearings I am continuing to drive it and after adding the Lucas the custer gauge stays normal I am currently looking for a replacement engine. but it is a daily driver and is running fine. Keep in mind that pressure is resistance to flow since I replaced the oil pump I know its working correctly you don't need alot of pressure for the engine to run until you put it under a heavy load. you are not alone here I bet if alot of these 4.0 engines had a mechanical gauge put on them they would read the same.
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Old 10-29-2010, 12:28 AM   #11
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Originally Posted by Gee oh Dee View Post
Can I have good oil pressure at the gauge but have BAD oil pressure elsewhere?
no
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Old 10-29-2010, 09:38 AM   #12
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no
From doing a little research I found this is incorrect. You can have a clogged oil port/passage (due to sludge usually) causing poor oil flow to certain places.

Finding this out would basically involve a major teardown and rebuild.
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Old 10-29-2010, 09:40 AM   #13
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"""""I'd like to have the "Check Gauges" light gone for good, unless it really needs to be on. """""

I think you'll find eliminating the stock oil pressure gauge insures the "Check Gauges" light will stay on.

That light is to tell you to "look at the gauges, something is not normal." With the stock gauge disabled, the gauge will read 0 - definitely not normal.

Start with replacing the oil sending unit (known to be defective often) - also look at the voltmeter - if it's not in the proper range it too will trigger the light, so will the temp gauge - or temp sending unit.
Not sure if it's also tied into the fuel level gauge, but it may be.

And - did you put a piece of wood or something under the battery to make it fit? Does the bottom of the battery fit flat on the battery shelf? Reason I ask is there's a battery temperature sensor under the battery - to prevent overcharging. If that sensor is not getting the reading in the right range, the PCM may suspect some kind of charging problem - and ask you to "Check Gauges."

BTW - that light will not throw a code or information like the Check Engine light does.
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Old 10-29-2010, 10:06 AM   #14
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"""""I'd like to have the "Check Gauges" light gone for good, unless it really needs to be on. """""

I think you'll find eliminating the stock oil pressure gauge insures the "Check Gauges" light will stay on.

That light is to tell you to "look at the gauges, something is not normal." With the stock gauge disabled, the gauge will read 0 - definitely not normal.

Start with replacing the oil sending unit (known to be defective often) - also look at the voltmeter - if it's not in the proper range it too will trigger the light, so will the temp gauge - or temp sending unit.
Not sure if it's also tied into the fuel level gauge, but it may be.
I understand what the function of the check gauges light is, and I understand its purpose. But thank you for clearifying it for me.

The issue I have with your suggestion is this: the Jeep is ours for life. Its never leaving us, not as long as my fiance and I are alive. So its going to have some serious miles put on it. That oil pressure sending unit you admit is a common problem will most likely cause problems again. I don't want to deal with it. There *IS* a better way, which is a mechanical gauge. I've already decided that is the route I'm taking. So I'm not going to replace the sending unit.

I've also stumbled across a few threads involving what I'm looking to do. What I've found is that you must ground a wire in the oil pressure gauge's system which will cause the factory gauge to peg at max pressure. The ECU does not care if the gauge reads too much pressure, it only cares if the pressure is too low. This will eliminate the false "Check Gauges" light, and will allow me to use it as it would normally function. The volt meter and water temp gauges will still trip the "Check Gauges" light if they need to. The only thing that won't happen is a "Check Gauges" light if oil pressure drops. But oil pressure gauges came long before "Check Gauges" lights and vehicles survived, so I'm sure I'll be fine.

Of course I haven't even mentioned the extreme inaccuracy of all the factory gauges, save speedo, tach, and fuel gauge. Water temp, volt meter, trans temp (its auto) will all be replaced/added in the future anyway.

On a side note, the fuel gauge is tied into a seperate fuel light, I'm not sure that its tied into the Check Gauge light as well.
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Old 10-29-2010, 11:20 AM   #15
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How 'bout a Tee and replace the sending unit. If that cures the light problem you have the mechanical gauge AND the check gauges to call attention to it if it's low?
Same with the Temp.

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