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Old 01-13-2014
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Join Date: Jan 2014
Location: Oak Ridge
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3.0L Engine Vacuum Question

I started my 99 Ranger tonight and saw that there was no oil pressure reading on the gauge. I shut it off and on several times with no reading. I then checked the oil and it was fine. in doing so I opened the oil filler cap. Then i started it back up and got a reading. the gauge measured half way. Not sure why i did this but as it was running I open the oil filler cap and the engine shut off due to the big vacuum leak.

Is that vacuum normal for the 3.0l, i have asked a few people and was told it may be depending on how ford did the vacuum for that engine.

Oh I am planning on replacing the PVC Valve and Oil sending unit.


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Old 01-13-2014
pearlkid9988's Avatar
Join Date: Dec 2008
Location: Newnan Georgia
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Honestly not sure I've never tried it. Ill run out and pull my cap and see what happens and report back!
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Old 01-13-2014
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Yes, it can be normal.
Engine idling has the highest vacuum it will have, so PCV valve is open and sucking air from valve covers and crank case.
When you opened the oil cap the extra air caused a lean mix and engine died.

Ford has used an oil pressure switch since the early '80s, so oil pressure gauge is really an Idiot Light without a bulb, lol.
If oil pressure is above 5psi then gauge will show "normal" if below 5psi then gauge will show 0.
Now before you panic, if oil pressure was really below 5psi you would hear the valve train loud and clear, that would be the time to shut off the engine.

0 oil pressure on the Ford gauge with no engine noise means check wire on sender or replace sender.
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Old 01-21-2014
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Join Date: Jan 2014
Location: Oak Ridge
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Thank You for your replies

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