'94 4.0 oil pressure problem help fast! - Ranger-Forums - The Ultimate Ford Ranger Resource


4.0L OHV & SOHC V6 Tech General discussion of 4.0L OHV and SOHC V6 Ford Ranger engines.

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Old 01-08-2014
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'94 4.0 oil pressure problem help fast!

When I'm driving around my oil pressure gauge stays at a normal range, but once I let off the gas it drops straight to red. So at red lights or stop signs I have to keep my feet on gas and brake. I'm getting nervous about it. Usually once I put it in park it will go back to normal for a minute then it will drop. So I cant let my truck idle. Please help it gets worse everyday. Thanks!!
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Old 01-08-2014
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I can think of a few reasons this might happen ...
(1) Oil too thick for wintertime [less likely]
(2) Oil pump failing [use mechanical pressure gauge to check for pressure fall off]
{a} worn out pump.
{b} if it has a pressure holding valve, may be stuck.
(3) clogged oil filter [also less likely]
(4) Oil gauge in instrument cluster is going [it is an electrical part, can get weak or compromised]
(5) Maybe also check for bad connection at oil sending unit, like oil in it causing a short. Also this sending unit can also get clogged.

How many miles on the engine, totally worn bearings give no resistance to the oil, so pressure drops. Also, do you have any major oil leaks, like a rear main seal, but you'd probably see this as a BIG oil spot on the driveway.

From your description it sounds like a sending unit failing/clogged. It doesn't actually determine varying pressure. Ford uses a on/off switch oil sending unit, if it senses pressure - it's on, no pressure - it's off, The gauge reads it as "good pressure" and sets needle to the middle of the arc.
My sending unit totally failed and said I had no pressure, and the "check gauges" light was on, engine ran just fine, no ticks or knocks. Replaced the sending unit, and "idiot light/gauge" went back to normal. So I would check this first, for my educated guess.

Lets us know how it goes.
Eric
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Old 01-09-2014
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My engine only has about 50.000 (it's been replaced) and I do have a very minor oil leak but nothing like a rear main. One thing I forgot to mention above is that it only does this when the truck gets warmed up. It won't do it cold. And when I turn the motor off the gauge stays where its at and very very slowly goes back to 0
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Old 01-09-2014
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Quote:
Originally Posted by Kasey View Post
My engine only has about 50.000 (it's been replaced) and I do have a very minor oil leak but nothing like a rear main.
Ok clarification post...
Used engine put in with 50k? or new/rebuilt which now has 50k? Was your original oil sending unit used on this "new" engine, and is it the same size/year/engine code as the engine that came out?


Quote:
Originally Posted by Kasey View Post
One thing I forgot to mention above is that it only does this when the truck gets warmed up. It won't do it cold. And when I turn the motor off the gauge stays where its at and very very slowly goes back to 0
Maybe someone who knows the early 90's engines, knows of an issue with this year engine or instrument cluster. But "Do" the mechanical pressure gauge check, to make sure your not going to seize this engine from lack of oil. A "dumb" gauge is liveable, bad pressure is not.

I hope someone else "knows" and posts here.

Good luck!
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Old 01-15-2014
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I figured it out! The gauge was just bad. I got a aftermarket one and hooked it up, and its just fine now! so glad it was an easy fix!
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