So I have wondered this since I bought my first Ford truck as a junior in high school, and have both heard and read conflicting reports about this: But in the 87-91 years is the oil pressure gauge a real gauge (directly reads oil pressure) or is it an idiot light disguised as a gauge? I would lean towards it being a disguise. But if anyone can confirm or deny that, that would be awesome. I am looking to put in a new cam in soon on my 88 and I want to get a real oil pressure reading so I can decide how worn out or not the engine is. If it is a low reading I might just elect to do a full rebuild. Any help is appreciated! (Its only got 166K and I have kept up very good maintenance on it, I bought it with roundabout 130K on it)

 

A few ways to tell...

Watch it as you rev the motor. If it shows increasing pressure as the engine RPM's go up it's real, if it stays put then it's fake.

Look at the sensor it's wired to. If it's a can or dome shape, it's real. If it's a round pancake shape it's fake.

Look at the electrical schematic for your truck. If it's real you'll see a variable resistance pressure transducer on the signal circuit. If you see a simple on/off switch or if you see a resistor anywhere in the signal circuit, it's fake.

Take the sensor out, plumb it to an air regulator and turn the pressure down to zero. Slowly increase the pressure as you measure across the sensor. If it varies evenly then it's real, if it shows open or a steady resistance reading that suddenly changes as you increase pressure past 5 or 10 PSI, it's fake.

Edit: and by measure across the sensor I mean use an ohmmeter between the signal terminal and the body of the sensor.

 

It's fake. If the oil pressure is above 10 psi or so, the gauge stays right in the middle. If it falls below 10 psi, the gauge plummets to zero. Those are the only two positions it ever takes. A real oil pressure gauge fluctuates as you're driving. At idle, the oil pressure will be relatively low. As soon as you start accelerating, the oil pressure goes up. The fact that the gauge never moves at all, whether you're idling, cruising, or full throttle accelerating, proves that it's fake. And even if it did fluctuate when driving, the fact that it doesn't have any actual numbers (10 psi, 20 psi, 30 psi, etc) makes it useless. What the hell is "normal" oil pressure anyway? That's like a speedometer that only has 0 mph on one end, 80 mph on the other end, and in between just says "legal speeds" instead of numbers in between. Worthless.

 

You're overthinking this. If it has real numbers on it (10 psi, 20 psi, 30 psi, etc) it's real. If it has some cryptic "normal" range with no numbers, it's useless and fake.

 

hahaha I knew it. well thanks for the clarification, I have argued with various people over the years that swear this is a real gauge, to which I vehemently replied, I highly doubt a real gauge wouldnt have numbers on the display.

 

In your 1988 truck and also the 1987 and older trucks would have a real oil pressure gauge.
1989 -1991 would have a fake oil pressure gauge.

 

Dixie I was thinking a voltmeter is a much better tool to measure with when something is disconnected from an electrical circuit. haha jk

 

Not necessarily unless you mean oil gauges specifically. Ford temperature gauges don't have any numbers either but they're real.

Useless, yes just about. Although I happen to know that the H mark on most factory Ford gauges is 250° and the C is I believe 140°.

Factory oil gauge lines up with the H mark at 10 ohms, with a "standard" Ford sensor this corresponds to 100 PSI.

I don't like it either...

 

All 88 F150s have the real oil pressure guage?
I am about to do the real oil pressure gauge mod on my 88 F150 302 but if I understand you correctly it is already their.
Trav

 

Lol see that's funny to us, but some people (usually thru no fault of their own but rather just due to inexperience) wouldn't know that. I have actually had to walk people thu how to do it by asking what model their meter was, downloading the manual for it, and then saying something like "connect one test lead to the left jack and the other lead to the middle jack, then set the dial 4 clicks from the left to the Ω symbol..."

 

If your sender looks like this, it's got a real gauge:



If your sender looks like this, it's a glorified idiot light:

 

Haha for sure. The struggle is real, I have most definitely done that to a couple buddies as well. Usually they call and ask me to "fix this fix that." Orrrrrr....I could teach you something instead of relying on someone else to fix it for you?
Thanks for the pics Jas. When it warms up later in the week I'll poke around a little bit and see what I got.

 

The 1988 F-series wiring diagram shows that you have the real thing.

1988 Gas F-series gauge wiring diagram:


/

 

I have the lower pic that Jas88 posted. The upper is what I understand is the real one.
Trav

 

Trav, you probably USED to have a real sensor but it got replaced due to this bull**** TSB from Ford. If so then just rip out the switch and resistance wire section, and swap in a real sensor.

TSB 88-05-14
LIGHT TRUCK: 1987-88 F-SERIES, BRONCO

ISSUE: An oil pressure gauge that indicates an erratic or low reading when the engine oil pressure is within specification may be caused by the oil pressure sender. The oil pressure sender may not work properly with the magnetic oil pressure gauge.

ACTION: To correct this, install a new design oil pressure switch and new design resistor wire assembly using the following service procedure. Refer to the oil pressure switch and resistor wire application chart for the correct service parts.

OIL PRESSURE SWITCH AND RESISTOR WIRE APPLICATION CHART
Engine Application Description Service Part No.
5.0L, 5.8L, 7.3L and 7.5L Oil Pressure Switch E6SZ-9278-A
4.9L Oil Pressure Switch E8TZ-9278-A
All Resistor Wire Assembly E6SZ-9F291-A

SERVICE PROCEDURE
1. Remove the existing oil pressure sender.
2. Install the new design oil pressure switch. Torque oil pressure switch to 10-18 lbs-ft (13-34 N-m).
3. Connect the female terminal end of the 20 ohm resister wire assembly to the oil pressure switch.
4. Connect the male terminal end of the 20 ohm resistor wire assembly to the vehicle wire harness.

PART NUMBER PART NAME
E6SZ-9278-A Oil Pressure Switch
E8TZ-9278-A Oil Pressure Switch
E6SZ-9F291-A Resistor Wire Assembly