Fluctuating Oil Pressure Gauge 94 class A

[mpaton]

Following on the heels of the fluctuating temperature gauge thread......

My 94 Winnebago Brave has had a fluctuating Oil Pressure gauge for some years now. In the past week, it's got bad enough for me to put in a tee and also have a mechanical oil pressure gauge whose nylon line only just makes it past the doghouse. I'd rather fix the existing gauge.

During a 2 hour drive, the needle will typically start around the 'N' of NORMAL, and may after about half an hour jump up to a higher reading, typically the 'M' or NORMAL, but also recently the 'A'. It may stay there for 20 seconds and then go back down to a lower indication. This may repeat a few more times.

The mechanical gauge reads a steady 63 - 66 psi through all this. No other gauges on the Ford Panel move around like this, although the Voltmeter habitually sits around an indicated 12 Volts instead of 13. Battery voltage at the chassis battery with the engine running seems a little low at 13.8, but the battery keeps a charge just fine.

This happened both before and after an engine rebuild, so I believe the mechanical gauge.

My dash is a 94, so no tach, Oil pressure top left, Voltmeter top right.

Although I'm told that around this time Ford replaced the oil pressure sensor in some trucks with one that acted like a switch, I believe that mine usually acts like it is a sensor.

What are the likely failure modes of the oil pressure indicating system. obvious candidates are the sensor, the wiring, the gauge, any voltage regulation for the panel.

I was initially going to PM Subford, but I thought we might all learn something.

[JohnRR]

Do you have any paperwork with the engine rebuild to indicate if the sender was replaced at that time?

If it was not that would be my prime suspect, if it was I'd suspect that a loose/frayed wire at the sensor end would have been caught at reinstall time which should eliminate that possible cause (but then again don't count on it).

Other than that as a last resort I'd do a wiggle test at the plug connection behind the dash panel.

[Hikerdogs]

You didn't mention what chassis your motorhome is built on. If it's a Ford chassis they had a small voltage regulator attached to the back of the printed circuit on the dash. If the regulator wasn't securely attached or started to fail the gauge readings would start to fluctuate. The 2 that showed the most fluctuation would be the oil pressure gauge and the volt meter.

Another thing that caused the oil pressure gauge to fluctuate was a bad connection at the sensor itself. I would first check the connector. If it' shows signs of rust, corrosion, or bad contact with either the wire or the sender replace it. If that doesn't cure the problem check the regulator.

[subford]

It would have to be the voltage is changing to the gauge.
There is no way the oil pressure switch on the engine can make the needle go passed half way up the scale.
If the wire is shorted to ground the gauge reads halfway on the gauge.
If the wire is open then the gauge read low on the scale (Zero Pressure).
If they installed a Oil Pressure Sender and not a Oil Pressure Switch then the gauge would read lower than halfway all the time if they did not jumper the resister on the back of the cluster.

There is no voltage regulator for gauges on the back of the cluster.
The extra board plugged into the cluster is the anti-slosh circuit for the fuel gauge.

The oil switch setup:


/

[JohnRR]

Quote:

Originally Posted by subford If the wire is shorted to ground the gauge reads halfway on the gauge.

For decades a common test of gauge wiring and the gauge itself testing has been to ground the wire out at the sender and the gauge would read maxed out, is there something unique about this system?

[mpaton]

Quote:

Originally Posted by JohnRR Do you have any paperwork with the engine rebuild to indicate if the sender was replaced at that time?

I rebuilt the engine myself, and I didn't replace the sender. The connection to the sender looks sound to me.

[subford]

Quote:

Originally Posted by JohnRR For decades a common test of gauge wiring and the gauge itself testing has been to ground the wire out at the sender and the gauge would read maxed out, is there something unique about this system?

Yes there is a 20 OHM resister in line with the oil switch to make the gauge only go halfway or to the center of the gauge.

The resister is near the same spot on the cluster for an F53 but the photo below is of a F-series truck. You can jump this resister and install an oil sender from an 80s truck to make the gauge read pressure as opposed to acting like a light bulb.


/

[mpaton]

Quote:

Originally Posted by Hikerdogs You didn't mention what chassis your motorhome is built on.

. I mentioned what i thought was quite a lot of information, but didn't include the chassis because I posted the message in the Ford Chassis forum. Are these messages perhaps cross posted to other forums that I don't know about?

Quote:

Originally Posted by Hikerdogs If it's a Ford chassis they had a small voltage regulator attached to the back of the printed circuit on the dash. If the regulator wasn't securely attached or started to fail the gauge readings would start to fluctuate. The 2 that showed the most fluctuation would be the oil pressure gauge and the volt meter.

I was aware of something attached to the rear of the cluster, but I wasn't certain what it was, and I haven't followed the wiring. However, we now know that Subford disagrees with you as to its function.

In any case while instrument voltage regulator failure could affect the Fuel, Oil and Temperature gauges, to have it affect the Voltmeter seems wrong to me. Voltmeters are usually intended as a cheaper substitute for an ammeter in that they can show voltage when battery charging and discharging is happening. If all it cam show is instrument voltage regulator output, then it isn't very useful. So I'll ask you to justify your statement about regulator failure affecting the voltmeter.

Quote:

Originally Posted by Hikerdogs Another thing that caused the oil pressure gauge to fluctuate was a bad connection at the sensor itself. I would first check the connector. If it' shows signs of rust, corrosion, or bad contact with either the wire or the sender replace it. If that doesn't cure the problem check the regulator.

That's been checked. Not a problem.

[JohnRR]

Quote:

Originally Posted by mpaton I rebuilt the engine myself, and I didn't replace the sender. The connection to the sender looks sound to me.

If it was not too expensive I think I'd opt to replace the sender just as a process of elimination.

edit;
I have to admit the resister Bill posted about has me second guessing myself about replacing it

Quote:

Originally Posted by subford Yes there is a 20 OHM resister in line with the oil switch to make the gauge only go halfway or to the center of the gauge.

See you learn something new everyday, thank you.

[subford]

The images below show the Anti-Slosh module and the oil gauge.





/

[subford]

A Photo of the Oil Sender that you DO NOT have:


A Photo of the Oil Switch that you DO have:


/

[mpaton]

Thanks Bill. You weren't that direct, but I am now pretty sure that the key to answering my original question is for me to realize that I have the resistor and effectively an oil pressure switch coupled to a meter, and I do NOT have a factory oil Pressure Gauge. I had heard that these panels originally had a gauge, but that too many people were complaining that their oil pressure would be lower at idle (as is normal) that Ford turned it into, effectively an idiot light in a gauge. Perhaps an Idiot Gauge? I had thought that this running change had happened around 1995, and did not affect the F53 chassis.

Evidently I was wrong.

Looking at the back side of my panel, I see the resistor. (must work out how to post photos). Also, ooking at my 1994 Ford Truck wiring diagrams document, I see that the 4.9L six cylinder truck has a "Sensor" and the other trucks and the F53 have a "Sender".

So even though my Idiot Gauge is fluctuating, I can still tell the difference between pressure and no pressure, and I don't need to be alarmed about sticking oil pressure relief valves. However I'll have to get to the bottom of it if I want to do the mod of shorting the resistor and fitting a proper "Sensor". Is there a particular sensor required for this mod?

You said that the device on the back of the panel was NOT a regulator, but is there a separate instrument voltage regulator somewhere, and what would its failure modes be?

A question on another mod. I had also believed that it was simple to change out my 5 gauge instrument cluster for the 6 gauge one(with tach) fitted to XLT trucks and later F53 CHASSIS. But it isn't simple; the wiring is significantly different. Can this cluster be used by repinning the 2 plugs n the back of the cluster, or is it more complicated than that?

[mpaton]

Exactly right; this is the one I have. Although mine looks a little different as it has a grey plastic cap over the brass stud, covering the black plastic of this photo. With the cap removed, it is just like this one.

If anyone's looking for it, it's on the rear top surface of the cast iron block, facing almost vertically upwards, rearwards of the intake manifold, just in front of the bellhousing attachment plane.

Quote:

Originally Posted by subford A Photo of the Oil Switch that you DO have: /

[subford]

No there is not an separate instrument voltage regulator anywhere.
I think that ended with the 1991 E-seires van.
Not sure if any F53 ever had one.

I replace my 1994 cluster with one with a tach from a 1992 F-series and yes I did do some wire swapping between plugs. It did not look like a 1994 or newer cluster with a tach from a F-series truck would work very well so I looked for a 1992 or 1993 cluster.
I have not look to see if a newer MH cluster with a tach would work as I think they would be very hard to find.

I also wired in some LEDs in the unused lamp holes going to the transmission wiring to tell me what shift solenoid was on and if the clutch solenoid was off or on. I also put in a toggle switch to lock the clutch in while going down hills.