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Discussion Starter · #1 ·
01 wrangler pressure is dropping when I stop. It drops down to 0. It's a 4.0. What could be causing this? I don't see any oil leaks.
 

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I've got the same problem. I replaced the oil pressure sensor and it didn't help. I have no leaks or loss in performance. I did start hearing a knock so I took it to my mech buddy. This was his diagnoses" your losing oil pressure cause 2 of your bearings are shot in the cylinder. The knock is the lack of oil getting to the top of your block because of the loss of pressure." He advised me to get a new engine, and oh BTW, mine only has 150000 on it. I'm not ready to give up on this engine, gonna replace the oil pump next week. I'm keeping my fingers crossed.
 

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Quite a few thing can cause it. Best bet would be to get a Mechanical Gauge (beg/borrow/buy) and check it. Then go from there. Good pressure? Then Sending Unit/Gauge is bad. Bad Pressure still? Bearings/Pump/holes.

I keep a Mechanical gauge around just in case
 

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Had the same issue when I bought an '02 4.0 with 70K.
replaced oil pump. didn't fix it.
Dealership said it was bas crank bearings.

Oil level was full on dip stick, but I noticed that I usually lost pressure when on the brakes.
I added another 1/2 qt, and saw some improvement.
Another 1/2 qt. and pressure loss was less frequent.
Another 1/2 qt. and problem solved.

I need every drop of 6 qts to keep the pressure up.
Try ignoring the dip stick and make sure you have 6 qts. of oil.
 

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Quite a few thing can cause it. Best bet would be to get a Mechanical Gauge (beg/borrow/buy) and check it. Then go from there. Good pressure? Then Sending Unit/Gauge is bad. Bad Pressure still? Bearings/Pump/holes.

I keep a Mechanical gauge around just in case
+1 Make sure the oil is full. Then check the oil pressure as per the shop manual and post the readings.
 

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Discussion Starter · #7 ·
I will. With the low miles could it be anything stupid that I am missing? They guy I bought it from didn't use it for over 6 months and it just sat in his garage.
 

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I will. With the low miles could it be anything stupid that I am missing? They guy I bought it from didn't use it for over 6 months and it just sat in his garage.

You're not really missing anything. The only question I have is how long is the oil in use? If you have a leaking injector/injectors they can cause the oil to be diluted with fuel and that will also drop oil pressure, and that's not good for the engine. Even if the oil level is full.
 

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Discussion Starter · #9 ·
I checked the oil and it is just at the safe level on the dip stick. With it sitting for so long does anything that it I topped it with some oil and used a engine clean additive to the oil that it would help?
 

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Might want to go ahead & Change the oil & filter if you are not sure how old it is or what weight oil is in it now,I would go with a 10w30 oil & Mopar or other quality filter should take 6 quarts including filter.
 

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I checked the oil and it is just at the safe level on the dip stick. With it sitting for so long does anything that it I topped it with some oil and used a engine clean additive to the oil that it would help?
Did you add an additive to clean the engine? If so what did you add? Some of these additives contain Kerosene and can thin the oil which would lower your oil pressure. I would also suggest changing the oil and the filter to the recommended viscosity for your engine and see if there is an improvement. Keep in mind it would still be a good idea after you change the oil to get oil pressure readings. Get your hands on a shop manual or Google what your oil pressure should be. They'll probably list a cold pressure at idle and at a certain rpm, then a hot pressure at idle and a certain rpm. Keep in mind the hot rpm reading will take a good half an hour drive on the highway to get the oil good and hot for the proper reading.
 

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Discussion Starter · #12 ·
Did you add an additive to clean the engine? If so what did you add? Some of these additives contain Kerosene and can thin the oil which would lower your oil pressure. I would also suggest changing the oil and the filter to the recommended viscosity for your engine and see if there is an improvement. Keep in mind it would still be a good idea after you change the oil to get oil pressure readings. Get your hands on a shop manual or Google what your oil pressure should be. They'll probably list a cold pressure at idle and at a certain rpm, then a hot pressure at idle and a certain rpm. Keep in mind the hot rpm reading will take a good half an hour drive on the highway to get the oil good and hot for the proper reading.
No additive was used yet. I was curious if anyone thought it was a good idea before I change oil to clean up any possible junk or sludge that could have built up from sitting so long.
 

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Cleaning junk/sludge up can be tricky, as you run the risk of dislodging things that might do more harm by plugging oil passages. If it were me, assuming you've ruled out a faulty sending unit and/or gauge, I would start with a conventional oil and filter change. Use this as a way to flush the system, so as not to waste more expensive synthetic oil. You can always change to synthetic later.

If that doesn't work, I would then pull the valve cover and check for sludge up top. The chances are the valve cover gasket needs to be changed anyway, so this will do no harm.
Next, I would pull the oil pan and see if the screen to the pump is plugged. Generally, if I'm going to go to the trouble of pulling the pan, I'll just replace the oil pump. Also, since your in there, you'll have the opportunity to replace the rear main seal. These are a two piece design, which are known to leak. The only thing to worry about with this one is that you take your time and not nick the crank when removing the old seal. Your call here though!

Lastly, word of warning, if you do replace the oil pump, please make sure you prime the pump, i.e. fill it with oil, before you bolt it back in. Also, make sure you remember to torque the oil pump bolts to the proper spec!
 

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I have noticed mine drops irregularly when the oil gets close to time to be changed, and after long interstate commutes at 75 or so.
 

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DesertRaider's mechanic was right on this one.

If you have changed your oil and filter and if you confirm oil pressure goes to zero at idle when fully warmed up with a mechanical gauge and you don't have a knock yet you will probably be able to get away with replacing the oil pump and the main bearings. One without the other is too risky. Do both. If you have a knock it is too late. You'll need a complete engine rebuild and a new crankshaft.
 

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Discussion Starter · #16 ·
I didn't know what type of oil was in there so I did an oil change with conventional oil. When it warms up it's at 45 or so than at idel or dead stop it at 10-20. I didn't put a different gauge on. This is what the dash gauge is saying.
 

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I didn't know what type of oil was in there so I did an oil change with conventional oil. When it warms up it's at 45 or so than at idel or dead stop it at 10-20. I didn't put a different gauge on. This is what the dash gauge is saying.
Those readings are fine, with these two important points in mind.

1. Verify the readings with a mechanical gauge.
2. The engine must be driven at least 30 minutes on the highway to determine the hot idle pressure. Your temp gauge can say the coolant is at normal operating temps, however the oil takes a lot longer to get to its normal operating temperature. A 30 minute drive or more on the highway will guarantee the oil is at the right temperature.
 
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