Oil Gauge wonky. Sensor or Sending Unit?

[PonyUp]

Hello again to All of you Teachers/Great people. I have a 1989 2.9 Eddie Bauer 4WD. My oil gauge is wonky as it zig zags up and down or it may be fine in the middle until it does it again. Most of the time is zigs zag now. No weird engine noises. I do not have a oil pressure gauge and I am thinking it may be cheaper to just go ahead and buy/change a part before taking it to a mechanic. They all charge $100+ just to drive into a bay. Are there two parts which have to do with the oil information to gauge? I know there is a small "unit" on driver side which has been changed out and that didn't make any difference. The sensor which plugs into the oil pan is the "level sensor"? If so, does it send info to the small unit on driver side by starter area? What sends a pressure reading to my instrument panel? Sorry, still learning and confused as I am seeing 2 different sensors listed online and they both say "Oil Pressure Sender". What is inside oil pan which leads to something plugging into it on outside of the pan? Where does that wire go? This link shows the one I had replaced. I couldn't get to it with any tool I have. Hence paid someone. Is there a special tool used to replace it? Thanks for any guidance/education. https://www.1aauto.com/ford-mazda-lincoln-mercury-oil-pressure-sender/i/1aosu00023?f=835066&gclid=Cj0KCQiA34OBBhCcARIsAG32uvPptlMhs9QTjqlDf7ns3ufCQSSHifrEGjbPECwWFV0rMg8Cea3_lx8aAofDEALw_wcB

 

[Steve1950]

Hey Dude,
I don't know anything about your oil pan sensor I just know a little about the oil pressure sender units that screw into the block. If your wire is grounding out anywhere it will cause the gauge to read possibly inaccuratly. If you had a needle gauge it would peg out if you grounded out the wire that attaches to the sender unit. That was one way to check you dash gauge to see if it was working at least on some of the older cars and trucks. I don't know about yours. Of course check for loose connections. Blessings

 

[Dirtman]

The thing on the pan is the level sensor. It does not in any way effect the guage. It gets wired to the idiot like on the guage cluster and turns the light on if the level is low.

The thing on the block is technically a switch not a sensor but when you are looking at a website it is most likely referred to as a sender. No real time information is sent to the guage. The switch is either on or off, when its on the guage gets power to go to the halfway mark when its off the guage reads zero. If the guage is bouncing around the switch is likely failing.

Never trust the factory ford oil pressure guage for actual data on your oil pressure because, it doesn't have any data...

 

[RonD]

Yes, change the Oil pressure sender its the most likely to fail part of the system

Make sure its for a 1989-1992 2.9l not earlier, its a switch in those years

Location drawing here: https://www.freeautomechanic.com/mechanic/forum/wp-content/uploads/2016/08/1990-ford-ranger-oil-pressure-switch-location-diagram.gif

Drivers side of engine in front of the motor mount on that side
It may or may not have the "stand off" tube
If you do have a stand off tube, pull it off as well, and make sure is clean inside, so pressure reaches sender
Do not tape threads, leave some bare metal threads so there is a good ground to engine, the sender only uses 1 wire so need engine ground to complete the circuit

In the same drawing you can see the OIL LEVEL sender, on the oil pan, not part of the oil pressure system
Oil level sender tells you when you are over a quart low on oil in the pan, a light on the dash will come on, "check oil" light
The wire and connector often break on these, if you check your oil then not really a needed system
But you can change the sender and splice a new wire when you change the oil next
Oil has to be drained first to change this sender, but oil pan does not need to be removed

 

[Dirtman]

Yes, change the Oil pressure sender its the most likely to fail part of the system

Make sure its for a 1989-1992 2.9l not earlier, its a switch in those years

Location drawing here: https://www.freeautomechanic.com/mechanic/forum/wp-content/uploads/2016/08/1990-ford-ranger-oil-pressure-switch-location-diagram.gif

Drivers side of engine in front of the motor mount on that side
It may or may not have the "stand off" tube

In the same drawing you can see the OIL LEVEL sender, on the oil pan, not part of the oil pressure system
Oil level sender tells you when you are over a quart low on oil in the pan, a light on the dash will come on, "check oil" light
The wire and connector often break on these, if you check your oil then not really a needed system
But you can change the sender and splice a new wire when you change the oil next
Oil has to be drained first to change this sender, but oil pan does not need to be removed

I thought they were always a switch

 

[RonD]

No, they used a PS60 sender until 1987 or 1988, then Ford changed to a switch and added a resistor to the back of the gauge

You can pull the dash and add a jumper wire, bypassing the resistor, and change back to a "real pressure gauge" up to 1995/1996 Rangers
In 1997 and up the resistor is internal so can't be bypassed

TRS article here on that change: https://www.therangerstation.com/forums/index.php?threads/variable-oil-pressure-gauge-modifiction.165083/

 

[PonyUp]

THanks. Got it on the one coming out of pan. Soooo...The thing "on the block is technically a switch not a sensor", is the one in the link I put in first post? If so, I changed that one. But when I look up Oil Pressure Sensor for my year, I am seeing 2 different ones in many places. https://www.partsgeek.com/catalog/1989/ford/bronco_ii/engine_electrical/engine_oil_pressure_sensor.html

 

[Dirtman]

The bottom one looks right to me. The top one looks like the "real" sending unit not the switch style.

 

[RonD]

The switch is small

"real" sender is 3 or 4 times the size at least

Yes, bottom one for sure

 

[Dirtman]

No, they used a PS60 sender until 1987 or 1988, then Ford changed to a switch and added a resistor to the back of the gauge

You can pull the dash and add a jumper wire, bypassing the resistor, and change back to a "real pressure gauge" up to 1995/1996 Rangers
In 1997 and up the resistor is internal so can't be bypassed

TRS article here on that change: https://www.therangerstation.com/forums/index.php?threads/variable-oil-pressure-gauge-modifiction.165083/

Poo, I always wanted to figure out how to get my factory guage on my 2009 to give a real reading, I knew there was a hack to make the guage read a real pressure but didn't know the hack didn't work post 1996.

I still think this is one of the dumbest things ford ever did. Trick people to think they have a guage but hook it to a switch for an idiot light. Whats the cost saving benefit here? Ditch the guage for an idiot light or make the guage read real! why make it fake? Did they save 4 cents and think the guage was a selling feature?

 

[RonD]

There was too much of a swing in oil pressure so un-knowledgeable people would bring in their Fords to complain about low oil pressure, this happened because people no longer knew how things worked

Oil pressure above 6psi is fine, but if the gauge needs to read from 0 to 80psi then 6psi looks very low
Oil pressure is the oil the engine CAN NOT USE at that moment, its the oil thats backed up in the main passage
Below 4psi you can start to get hydraulic lifter noise(rockers), so anything above that is fine

With higher RPMs you get even more unneeded oil backing up in the passages so oil pressure goes up to 30-40psi when driving, so the sudden drop to 6-8psi at idle freaked people out, "something must be WRONG"

So for 99% of drivers the oil pressure switch is a GOOD thing, no freak outs
Oil pressure switch is set at 5.5psi, below that switch is open and gauge shows 0, above that and its closed and gauge shows "normal"


I prefer the Oil Light myself vs a gauge
Although my Wife is part of the 99% and ignored the oil light(s) after her oil pan was punctured
Fried her engine
When I ask why she didn't pull over when BOTH low oil light and the oil light came on she said..."well, if it was THAT important you would think there should be a buzzer as well"
Can't argue with that logic

 

[PonyUp]

There was too much of a swing in oil pressure so un-knowledgeable people would bring in their Fords to complain about low oil pressure, this happened because people no longer knew how things worked

Oil pressure above 6psi is fine, but if the gauge needs to read from 0 to 80psi then 6psi looks very low
Oil pressure is the oil the engine CAN NOT USE at that moment, its the oil thats backed up in the main passage
Below 4psi you can start to get hydraulic lifter noise(rockers), so anything above that is fine

With higher RPMs you get even more unneeded oil backing up in the passages so oil pressure goes up to 30-40psi when driving, so the sudden drop to 6-8psi at idle freaked people out, "something must be WRONG"

So for 99% of drivers the oil pressure switch is a GOOD thing, no freak outs
Oil pressure switch is set at 5.5psi, below that switch is open and gauge shows 0, above that and its closed and gauge shows "normal"


I prefer the Oil Light myself vs a gauge
Although my Wife is part of the 99% and ignored the oil light(s) after her oil pan was punctured
Fried her engine
When I ask why she didn't pull over when BOTH low oil light and the oil light came on she said..."well, if it was THAT important you would think there should be a buzzer as well"
Can't argue with that logic

Thanks Ron and everyone else. As I was driving today, the gauge went from the middle all the way over to the left after I drove it about 15 miles. Never moved from that left spot. Car sat several hours and it was in the middle for a couple of minutes , then went to almost all of the way to the left again. Gage has remained in the middle for 3 years until 1 1/2 years ago. Stopped at parts store on way home from work. I got the small one which they said is for cars with the oil gauge in the dash/instrument panel. I also got the socket which is supposed to make it easier and not damage the unit. Mine does have the "stand off tube", clean it with brake cleaner? No teflon on it either? I unplugged the wire off the unit and used a wire with alligator clips to check the wiring itself. Yeap, when grounded, Oil pressure needle went above the half way mark. I think that means wiring is good, sensor is bad? But>>I have changed it out twice now in past 1 1/2 years and it made no difference. Trying a third time. IF...., installing a new one again still doesn't make gauge work, can I use a Oil Pressure test device to plug into the block where the sending unit screws in? Do I need a special test kit to test from there? What should the pressure ideally be?

 

[RonD]

With oil pressure switch wire grounded to engine or battery negative, then with key on oil gauge should go to 1/3rd to 1/2 way and stop
If it goes up more, then its a gauge problem, and should always stay in the same place over the years, its an electric gauge not a pressure gauge
So if it goes up and down check the alternator

The gauge is set to read a direct ground and show needle in the "normal range"
A bad wire would show nothing on gauge, corroded wire would read low on the gauge

Not sure there is anything external that could make the gauge needle go higher that say 3/4
You have a 1990 so could be the resistor on the back of the gauge could be the issue, if there is no resistor gauge will go all the way up, like a "real" oil pressure gauge would do when grounded directly
That's why you need the jumper on the back of the gauge to bypass the resistor so a "real" pressure sender can send the Variable Ground to the gauge

Yes, you can install any type of a sender you want in place of the switch, they all used the same threads

You can put sealant/tape on the UPPER threads, just leave a few lower threads bare for a good ground if you use an electrical type sender

 

[PonyUp]

Hmmm...It had been zig zagging all over the place when it was not in the middle untill today when it went left all of the way and stayed there. I did the ground from switch wire to battery negative and got just above the halfway mark. New alternator 2 years ago but I was looking at alternator today and noticed a huge amount of carbon buildup on the front driver side "grill" of it. Car is never used off road and I do drive mainly highway driving. But there is heavy carbon there. Not sure what it means but all other electrical things are fine as of now. This my 1989 daily driver. The 1990 was wrecked but repairable and I bought it back from insurance for $200 as a total since they like to total them at $4000. I got the 1990 back from total repair just 2 months ago. It has a couple of issues I will address in a different thread later. I just never saw any carbon buildup on the front of a alternator before. Maybe it is going bad? Will change out sending unit in morning. I suppose it is time for me to buy a Oil Pressure test kit and learn more since I don't have to remove 20 things to get to it. Thanks again RonD. You make a non mechanic owner of Broncos much much less frustrating.