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90 F150 - Loss of Oil Pressure at High RPM/s

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Old 02-29-2012, 02:30 PM
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90 F150 - Loss of Oil Pressure at High RPM/s

Ok heres the issue ...

I was driving to church the other day and I just happened to look down at my Oil Pressure Gauge and it started radically jumping off and on and then eventually shut off ... I pulled over and let it sit a minute and started it back up and the oil pressure returned and was consistently on ... Once i got back on the road and was driving for a few minutes it repeated and did the same thing , so i pulled over and did the shut off and turn on and again it returned ... needless to say it was a long drive home pulling over every couple miles ... Sitting in the driveway idling it is fine, even up to normal temp, but once its up to normal temp i start revving it up and you can start to hear the lifters and/or rocker arms start to make a clicking noise as in a loss of oil to it, but no drop in pressure shows when in drive way and revving (only when driving)

Here's what i tried , givin I'm less than 100 miles since last oil change ... First I pulled the Oil Pressure Switch and replaced with a new one , didnt fix the problem ... Then I figured a 22 year old pickup would have quite a bit of sludge build up in the engine so i decided to do an oil flush , poured bout a third of a can of SeaFoam into the oil and ran it in the drive way at idle for about 45 minutes, sitting at idle there is no noise, but again once i start revving it up the lifter or rockers start clicking (no pressure drop shows) the noise continues til i shut it off for a minute and restart and noise diminishes ... drained the oil and replaced with some cheap stuff and repeated the SeaFoam process one more time , no change ... drained the oil once last time and put the good stuff in along with replacing one quart of oil with Lucas Oil Treatment ... Once all done I decided to run it around the block , it ran good for about 3/4 of a mile and once again the Pressure Gauge started jumping radically again ... Any Ideas?? I was thinking maybe the Oil Screen and Oil Pump, but not an easy job replacing, being that I need to undo engine mounts and prop engine up just to get to the Oil Pan bolts that are blocked by the cross member ... Any info would be greatly appreciated ...

On a side note I have recently replaced the Timing Gears , had issues getting Timing Gear off and on the CamShaft , putting it back on there was about 1/4" of play back n forth on the CamShaft , but once it was seated properly the shaft held steady at good location , not sure if any of that makes a difference but all information helps ... I do know that the Oil Pump is ran off the distributor , so i was also told that maybe where the distributor shaft goes down into the oil pump could be worn out and not making a good grip on the oil pump, which could cause it to seem ok during idling and at high RPMs it loses grip and starts to slip, thus dropping oil pressure ... I dunno ...

Thanks guys !!

Last edited by TruckDawg; 02-29-2012 at 02:41 PM.
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Old 02-29-2012, 02:44 PM
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Did you replace the oil filter after any of the last oil changes? What brand of oil filter are you using?
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Old 02-29-2012, 02:48 PM
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Of course, after each Oil Flush treatment i replaced the oil filter , sure there was major sludge in it after the SeaFoam, so i replace everytime after an oil change .. I used a standard Fram filter
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Old 02-29-2012, 02:56 PM
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Fram oil filters are really bashed on this site. I doubt if the fram filter would be the cause of your problem. You can buy Motorcraft oil filters at Walmart or Advance Auto for not much more than Fram.
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Old 02-29-2012, 02:56 PM
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you have pushrod style engine so its not like your motor is freaking out like modulars do. the filter may have exploded to if it was the filter though. your pump probably isn't keeping up with the rest of the motor on rev.
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Old 02-29-2012, 03:51 PM
glc glc is offline
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Plugged oil screen. You need to drop the pan.
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Old 02-29-2012, 03:52 PM
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I just pulled the Distributor out to look at the end of the shaft that goes into the Oil Pump ... the end of the shaft looks fine, not stripped or anything, looks like it seats down in there about 5/8" , not sure if it should be seated further down in there ... took a screw driver and stuck it down in there and manually turned the oil pump ... felt very resistive on turning , but does turn in both directions with both being resistive, not sure if it should turn easily ??
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Old 02-29-2012, 04:39 PM
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You need to check it with an actual pressure gauge not that junk in the dash.
I'd say the screen is gunked up though.
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