Question about 1999 Jeep Grand Cherokee

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Loosing oil pressure on idle check engine light on

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First, verify actual oil pressure using an external test gauge.
There are two major reasons for oil pressure loss. first is worn engine bearings (usually rods but can be crankshaft or cam bearings as well)
Other reason is a oil pump screen that has been partially obstructed with hard carbon deposits due to low quality, high paraffin oil.
Chances are that the next fifteen people will tell you to replace the oil pump. 99% of all pumps do not fail by themselves. Replacing the pump will often raise pressure for an hour or so but the problem will shortly return.
The cause is a worn bearing, allowing pressure bleed off at the crankshaft.
The pump can be internally scored by debris from a bad bearing but even a scored pump will often not loose more than a small percentage of it's pumping ability. It is always a good idea though to replace the pump whenever a bearing or bearings are being replaced.
If you don't yet hear any knocking, still could be a bad pressure sender though so check as I recommended before going into any larger repair.
You won't see bearing wear with your eyes...you need to measure it using plastigage.
good luck....hope it's just the sending unit!!

Posted on May 29, 2010

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