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Oil Pressure


blu44

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May 7, 2014
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97 ranger 4.0 245xxx Oil pressure sensor replaced about 6 months ago

Just get it inspected and registered on the way home 3 blocks from my house she start knocking. At the light before my house the oil pressure goes crazy i immediately turn her off. The ol lady comes and gets me and pushes it to the store next to my house. A few hrs later i come get it start it up she seems to run fine i take her home.

Next morning i'm like that was weird i start her she runs fine. So i tell myself let's see what happens i plan a trip to my buddies house about 20 miles away. She took about 4-5 miles to warm up and once she did the knocking comes back and the oils pressure goes crazy and she starts smoking under the hood. I shut her off and the ol lady comes get me.

Come back about dawn put some heavier oil in her. Again she strats right up and runs fine. Again temp take about 4-5miles to warm up. Get her back to the light before my house oil pressure goes crazy.

i haven't done any compression or leak down test. I feel maybe the oil pump is going out any ideas.
 


RonD

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1994
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Ford
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Around 1987 or so ALL Fords got oil pressure switches.

The dash board gauge is now an Idiot Light, so either ON or OFF
The oil pressure switch on the engine turns ON the gauge when oil pressure is above 5psi, most gauges shows from 1/4 to 1/2 when ON
Under 6psi switch turns OFF, which would be no pressure, 0, on the gauge

So if gauge "going crazy" means it is going up and down then pressure was hovering between 0 and 6psi actual pressure

Then knocking means actual loss of oil pressure, so engine should not be operated
If it was "ticking" noise that is different, valve train is first to lose oil pressure and while not good it can take a bit of that without damage

Knocking means damage is done, higher oil pressure from thicker cold oil is just hiding the knock a bit better than warmed up oil.
So time to pull engine for rebuild
If it is a "knock" new oil pump won't help
Crank or connecting rod bearing is what "knocks", and the knock is because there is now a gap between bearing and journal.
That gap is also where the oil pressure is going.

Oil pressure comes from oil pump providing MORE OIL than will fit thru the bearing gaps, so it backs up in the main passage, oil filter, where oil pressure switch is.
If a bearing gap opens up then oil flows out faster so pressure drops, and less back up when cold and no backup when warm
 
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