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1994 Ford Ranger XLT 4.0L oil pressure help

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What's up TRS community, long time lurker, first day register.

So here's my problem:

My oil pressure has a tendency to drop real low, and the needle wiggles below L when I floor it, or when I attempt to pass someone on the freeway.

It drops when I hit 3.5k RPM or higher, and it bugs me. It does the same when I had a mechanical gauge installed.

I'm not burning oil, and just had an oil change about 300 miles ago. I also just changed out the spark plugs and wires, which helped a previous misfire problem.

Has anyone had this issue, or have any clues as to what to check? I bought this truck a little over a month ago, and this is probably the only big problem.

Thanks, Don.
 


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RonD

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1994 will use an oil pressure SWITCH on the engine.
Under 5psi = 0 oil pressure
Over 6psi = Full oil pressure

No in between, if there are, then that is an electrical issue or switch is failing.

You hooked up a mechanical gauge?
So you installed a PS60 oil pressure sender on the engine, removing the switch?

Or used an oil line to pressure gauge, and removed switch?
 

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1994 will use an oil pressure SWITCH on the engine.
Under 5psi = 0 oil pressure
Over 6psi = Full oil pressure

No in between, if there are, then that is an electrical issue or switch is failing.

You hooked up a mechanical gauge?
So you installed a PS60 oil pressure sender on the engine, removing the switch?

Or used an oil line to pressure gauge, and removed switch?
I eliminated the switch all together. And it still have pressure reading lower than an engine should. I'm fed up with it at this point, trying to figure it out.
 

RonD

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Oil pressure reading is back pressure at the oil filter/main passage.

Its excess pressure, so it is oil the engine can't use.
As engine RPMs increase oil demand increases and oil pump speed increases.
Oil pump flow increases more than oil demand so the oil the engine can't use should go up, yours is going down.

So it could be pick up screen is clogged up, oil pump flow can't increase beyond a certain point but oil demand does, or oil pump pressure relief valve spring is weak or loose, so opening at lower pressure than it should.

4.0l should be about 7-9psi at idle, 700rpm
Then run up to 25-30psi at 3,000rpm

Just as a heads up I have read about people using RTV sealant to redo oil pan gasket, and maybe a bit too much, lol, the RTV drys and breaks off in little balls inside the oil pan, these find their way to the pickup screen and stay there, building up over time.


You could do some tests on the oil pump with a drill powering the pump via the "Distributor hole" in the top rear of the block.
You should see a steady increase in oil pressure as drill RPMs increase, engine demand is low since bearings are not spinning.
 
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Oil pressure reading is back pressure at the oil filter/main passage.

Its excess pressure, so it is oil the engine can't use.
As engine RPMs increase oil demand increases and oil pump speed increases.
Oil pump flow increases more than oil demand so the oil the engine can't use should go up, yours is going down.

So it could be pick up screen is clogged up, oil pump flow can't increase beyond a certain point but oil demand does, or oil pump pressure relief valve spring is weak or loose, so opening at lower pressure than it should.

4.0l should be about 7-9psi at idle, 700rpm
Then run up to 25-30psi at 3,000rpm

Just as a heads up I have read about people using RTV sealant to redo oil pan gasket, and maybe a bit too much, lol, the RTV drys and breaks off in little balls inside the oil pan, these find their way to the pickup screen and stay there, building up over time.


You could do some tests on the oil pump with a drill powering the pump via the "Distributor hole" in the top rear of the block.
You should see a steady increase in oil pressure as drill RPMs increase, engine demand is low since bearings are not spinning.
I didnt want to believe it would be the screen, mainly because im not a fan of pulling the oil pan... im a diy, but it seems a bit more sensitive and touchy. :sad:

being 17, my father tends to try and make the decisions for me... and hes refusing to let me change the tranny fluid, for instance, so i doubt he'll let me pull the pan.

your response taught me alot though, and the next time i get the time, ill brace to try the drill test.
 

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I am not sure but when I drove a ford in korea with the v6 cologne engine I was told the oil pressure came from the camshaft bearing. I have the same basic problem as you do, I have over time replaced the switch (some change) but it again went to reading low. I bought the pieces for a oil gauge just never installed. I have had the oil pump changed and the pan was cleaned and so the pick up was also cleaned and I still have the same problem. Recently it started to hold at the R in normal first crank but drops as it is driven. Also the water temp has dropped and no longer registers so not sure if its something in the dash that is the actual problem creator. Using 40 wt oil makes no difference so really dont think its a pressure problem but just an indicator.
 

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I am not sure but when I drove a ford in korea with the v6 cologne engine I was told the oil pressure came from the camshaft bearing. I have the same basic problem as you do, I have over time replaced the switch (some change) but it again went to reading low. I bought the pieces for a oil gauge just never installed. I have had the oil pump changed and the pan was cleaned and so the pick up was also cleaned and I still have the same problem. Recently it started to hold at the R in normal first crank but drops as it is driven. Also the water temp has dropped and no longer registers so not sure if its something in the dash that is the actual problem creator. Using 40 wt oil makes no difference so really dont think its a pressure problem but just an indicator.
I have abnormally low water temp, but I'm less bothered. It just seems weird, and makes my head spin trying to figure it out.

Like nothing physically seems broken or bad, and I'm not even gonna try and pull my engine just to check.

It idles fine, so I mean. Guess I file this as, "aging" problems vehicles get.:annoyed:
 

Andy D

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My credo
to prevent Found On the Road Dead, Fix Or Repair Daily
What are you using for oil? I'd run some 10 w 30 :D
 

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Okay I sort of forgot about this thread that I made butt new developments. I just recently put a new exhaust in my Ranger on Sunday with a Flowmaster 40 series Delta sounds great.

But after I did that my oil pressure problem went away for the most part. I'm able to get it wrapped up to like 5000 before it even shows any pressure decrease.

My truck is basically a mystery house on four wheels.


I got a new question. My transfer case is making a weird clicking and then periodic clunking sound when in 4 wheel drive. I have a feeling I'm going to have to either rebuild or replace my transfer case.

Can I interchange per se a 3.0 transfer case from a Ford Ranger to my 4.0? Or is that just not how transfer cases work?
 

Andy D

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OP sensor has a loose connection. Of all the things it may have been you had the cheapest. :D
 

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OP sensor has a loose connection. Of all the things it may have been you had the cheapest. :D
Haha yeah. Let's hope it stays that way :)
 

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did some fuel pressure repairs dropped my gas tank and fixed a seal replaced some lines got my fuel pressure up 10-15 but my oil gage states higher now and even fluctuates a little above the high mark with some rpms … I had to burp my radiator once but it still staying up higher than normal …. ive did an oil change recently with all my repairs and such but im still in the the dark my oil was also past the fill mark a pinch for a while im thinking the newer detergents may have freed space/sludge in the switch ...is it more accurate now ? ;/ I don't like the swings in the needle ive never seen before from high to a little past the high mark
 

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The 1994(1989 and up) oil pressure gauge is an on/off setup, any fluctuations are electrical

The oil pressure SWITCH(on/off) on the engine can get sludge in its passage, so can read off/on causing the changes in gauge

Switch shows OFF below 5psi, ON above 5PSI
This is simply a no Ground off, and Ground on

You can convert 1994 to a "real" oil pressure gauge, seen here: https://www.therangerstation.com/forums/index.php?threads/variable-oil-pressure-gauge-modifiction.165083/

PS60 Sender works
The senders use a variable ground, like a temp sender does
But you need to by pass the resistor on the back of the gauge to get it to work
In 1995, I think, Ford put the resistor inside the gauge, so hard to change those
 

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