OIL PRESURE DROPPING

[91expl-sport]

I HAVE A 91 EXPLORER 4.9 V6 AND ABOUT A MONTH AGO THE OIL PRESURE GUAGE MOVED FROM THE (M) IN (NORMAL) TO THE (R)AND BACK TO THE (M) THE NEXT DAY. SINCE THEN I CHAGED THE THERMOSTAT (JET 180),OIL(ROYAL PURPLE SYNTECH,FILTER (MOBIL ONE) PLUGS(BOCH PLAT 4, AND WIRES ADDED A K&N FILTER CHARGER TO THE TRUCK. ALSO CLEAN THE TROTTLEBODY AND MAF SENSOR.

PROBLEM:

WELL TODAY THE IT WENT FORM (M) IN (NORMAL) TO ALMOST TO THE (O)...PARKED THE TRUCK AND REPLACED THE OIL PRESURE SENDING UNIT OR SENSOR.. STILLING HAVING THE SAME PROBLEM BUT THIS TIME ITS MOVING TO THE (R) FROM THE (M). THERE IS NO KNOCKING SOUND FROM THE LIFTERS OR LOST OF POWER..

 

[Exploderman]

mine: 94 Sport 97,000 miles.

I've seen the same thing happen with mine 3 times.The first time it dropped from "A" in normal to "O". It stayed that way for a few miles until I was passing a car and shifted to 3rd (manual trans) and stood on the pedal.
As the tach passed 4,000 I happened to see the pressure jump back to where it usually was.
Has happened 2 other times and a quick engine rev to about 4,000 has made the problem go away.
Go figure! At first I thought it was crap in the presssure sensor. Now I don't have a clue!!!


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[BubbaF-150]

I hate to tell you this, but I highly doubt anything you can do will stop your problem. My truck used to have a 300 straight-6 in it, which had that exact problem starting at 105k mi. At first, it would just dip from the "A" to the "R" and come back up as soon as I revved it a little. Over time (25k), the dips got worse, and it took more revvs to get it back up, until finally, it just stayed down on the "R". I continued to drive it for another 30k, and the pressure continued to decline until at 160k, it was between the "N" and "O". It didn't spike up or down, but the pressure was too low for my liking. I probably would have fixed it, but it met a worse fate - a blown lower rad. hose, locking the thermostat closed, letting the temp. gauge read normal while it cooked itself into oblivion. It has since been replaced by a 351W. I beleive the cause of the oil problem is excessive clearances in the main, rod, and/or cam bearings, but if you are lucky, it may just be a worn out oil pump. Try the pump first, if that's not it, you have my sympathy. Good Luck!

[This message has been edited by BubbaF-150 (edited 01-22-2000).]