Oil pressure gauge showing no pressure?

[srisitt]

I recently bought a 91 4.0L that shows no pressure on the dash gauge. The previous owner was driving it like this and I drove it 300 miles to get it home and it ran just fine. If there really wasn't any oil pressure I imagine the engine would have been noisey as hell and died soon after I pulled away, so it must be something else. Still I want to fix it.

What can I do to diagnose the problem? Can't find any info on this in my manual.

 

[Dirtman]

Replace the sending unit, they fail quite often. They only cost a few bucks. It's actually just a pressure switch so the guage is kind of misleading. When the switch is "on" the guages goes to the halfway mark, there's no real pressure reading.

And yes if you truely had zero oil pressure your engine would be a boat anchor within about 30 seconds...

 

[srisitt]

Replace the sending unit, they fail quite often. They only cost a few bucks. It's actually just a pressure switch so the guage is kind of misleading. When the switch is "on" the guages goes to the halfway mark, there's no real pressure reading.

And yes if you truely had zero oil pressure your engine would be a boat anchor within about 30 seconds...

Thanks! Do you know where I could find one of these for a reasonable price? I usually get parts on rock auto and theirs is $180

 

[Dirtman]

Ummm i dunno what you looked up but the oil pressure sender for your truck on rock auto is $2.35....

Oil pressure switch

 

[Grumpaw]

Thanks! Do you know where I could find one of these for a reasonable price? I usually get parts on rock auto and theirs is $180

Rock Auto has em for just a few bucks...don't know where you got 180 bucks...
Most expensive one on their list for your 91 Ranger is $18.20, and thats for a Ford/Motorcraft unit.
Any local auto parts store should have them in stock...it's a pretty generic part.
Grumpaw

 

[91stranger]

I would get one locally. They are pretty cheap and easy to change. Mine went bad on my 91 and I replaced it and put too much Teflon tape on the threads and it wouldn't read anything on the gauge. This could be the case if it was recently replaced. If not, just go buy one and put it on. Mine was called a "knock sensor"

 

[Dirtman]

Knock sensors are small acoustic sensors set to a specific frequency to detect knocking and pinging so the ecu knows the limit it can advance the ignition timing.

Not sure how you got that mixed in with an oil pressure sensor?

 

[srisitt]

Ummm i dunno what you looked up but the oil pressure sender for your truck on rock auto is $2.35....

Oil pressure switch

My mistake, I was looking at the wrong part. Thank you!

 

[Uncle Gump]

Wow...

Yep... just Wow

 

[adsm08]

Mine was called a "knock sensor"

No, it wasn't. Just no.

 

[ratdude747]

You could fix this the way I fix them... a little more involved but IMHO worth it:

https://www.therangerstation.com/fo...riable-oil-pressure-gauge-modifiction.165083/

(the original post is a tech article, but I later wrote an addendum for the 4.0 specifically since the process was slightly different)

 

[srisitt]

I installed a new sender and it still showed no pressure after I started it up and let it idle a few minutes. This truck leaks power steering fluid, I noticed the connector the sender is wired to (is this the oil level sensor?) has gotten pretty soaked, wonder if that has something to do with it. Should be able to check continuity with a meter. Anything else I could look at?

 

[fastpakr]

What happens on the gauge if you connect the wire going to the sensor directly to ground?

 

[srisitt]

What happens on the gauge if you connect the wire going to the sensor directly to ground?

Do you mean disconnecting the wire at the sensor, connecting it directly to ground, and leaving the wire boot connected to the sender? How would I connect directly to ground from beneath the truck?

 

[srisitt]

I cleaned some of the grime off the sensor assembly and found the wire going to it is stripped bare. The rubber grommet was hanging loose back on the wire too. Looks like I'll probably need to switch out the sensor and the wire yeah? Maybe I'll try just the wire first.