Every time I have had an ICVR fail or begin to fail on me, the gauges would do just as ND said and swing all over the place. One minute full oil pressure, next minute next to none, start driving and it'd shoot up again, on and on and on.

My bets are still a faulty ground somewhere. Likely behind the cluster where most of them are. A new ICVR is cheap enough though, so if you felt so inclined to do a quick swap it's not all that hard. IMHO I prefer the transistorized ones that ya either build yourself or buy aftermarket, but if youre looking for a quicker "drop in" alternative, an OEM style one that your local AutoZone can get will work just as well.

 

Check the wiring leading away from the oil pressure sending unit. Look for wear, or a break in the insulation. Its a long shot, but there may be a section worn thru that allows the wire inside to sorta make a ground connection to the engine block or valve cover or such & send your gauge up the scale.

 

Not a bad idea to check the wiring as well as scottscott suggested. My guess is that if that were the case though, that the issue of the enhanced gauge reading would only he on occasion instead of all the time.

But either way, worth a check by all means.

 

update;
Took out the instrument cluster again, removed the ICVR cleaned it and the circuit board where it goes, then put a dab of di-electric on it and made good ground. plugged back in truck and tested the ICVR had 12 on one side and fluctuating 5 on other side. Also tested oil gauge by removal of wire and grounding to block gauge pegs at top. One difference now since removing wire to test gauge , with wire back on sending unit the gauge reads at 90% even after warmed up . still baffled......

 

a friend was using his test meter when testing ICVR and the reading of 12 volts on the one side was not a stable needle it jiggled a little but he said it was prob. the meter . when we saw the 5 volts it was moving up and down noticeably

 

What weight oil are you running? I'm running 10w40 in the winter now, but in the summer I run 15w40 Rosella diesel oil (thank you Wisconsin winters for making me change out good oil...). What pressure readings are you seeing with an analog gauge?

Honestly I think your set up is just fine. You've checked everything from sending unit to gauge and everything in the middle.

Maaaaaaybe someone more advanced than I has specs for it, but I (thought) there was a scale for the resistance values off the sending unit.

If you're really worried about it, maybe try another brand of sending unit? The gauge runs on resistance measurements so maybe one brand would differ slightly to the next?

I'm honestly grasping at straws here, but if I were you, and I was REALLY worried about it, I would buy both an ICVR and a new sending unit.

First I would swap sending units again. See if that changes it.

If no change, reinstall first sending unit and replace the ICVR.

If no change, reinstall new sending unit, leave new ICVR installed. That's all you can do!

There is an adjustment screw on the back of the ICVR, but it is such a touchy (and I mean touchy and FRAGILE) adjustment, I honestly don't recommend anyone play with it. But....the adjustment screw in most cases can be turned with a needle nose pliers a 1/4 turn at a time. Note it is glued in place from the factory, but if you chip it out with a razor, you could grasp the screw with a needle nose pliers and turn it.

I forget the direction and their correlation, but one way will increase voltage output from the ICVR, and one way will decrease voltage from the ICVR.

BEAR IN MIND: The voltage leaving the ICVR controls the readings of ALL the gauges. More voltage = more gauge movement. If all your other gauges work and read fine, I would leave it alone and buy a solid state ICVR from somewhere online or fab your own (I have instructions for this as well if interested).

End of the day, to me it sounds like your motor and oil pressure gauge system is healthy as it is!

 

Sounds like you were using an analog meter instead of a digital one? If so, excellent! You saw exactly what the regulator does. Neither signal is rock solid perfect like in a new car, but the large amount of needle movement in the 5V post shows the regulator is still working.

The regulator is really a bimetallic spring wrapped in resistance wire that changes shape as it heats up/cools down to make contact internally. The resistance in the wire drops the voltage, heats the internal wire, bends the springs, contacts the points inside it, and gives ya your 5V reading. The fluctuations occur when the wire contacts the point, then momentarily cools off, changes shape again, and breaks the contact at the 5V pin. This causes the 5V pin readout to fluctuate between 0 and 5V many many times per second. If we had an oscilloscope, we could see this in wave form, but now I'm diving too deep.

My typing this all on a phone is a challenge!

 

When testing the ICVR with friends volt meter and the 12 volt reading moved a little but friend said it was prob. the meter , the 5 volt reading was fluctuating .

 

Live in Phoenix AZ so in summer at 118 deg. I run 20-50 and now in "winter" lol I run
10-40 . Originally from NW Washington so lol at what winter is here..
When I started having this problem, took to shop and they removed the sending unit and checked pressure with screw in gauge in was reading proper pressure at operating RPMs. That's when a new oil sending unit was put in since I didn't know how old the original was.

 

Then I would say try replacing the ICVR with a new one, or building one of your own. otherwise your truck sounds pretty normal!

 

the shop that I have gone to before the owner is a FORD truck guy and one of the mechanics has a 4x4 F150 same yrs, so will take it there in morning to check into wire coming from sending unit , he also had a similar problem with his truck and fixed it . will find out if it's the same or a different prob. with the gauges. Will update after shop visit.

 

replace the ICVR even though it reads good?.. would it change the high reading that the oil pressure gauge now shows ?

 

Re read post #21. It is possible that the internal resistance value between a new and your current ICVR may be different. That value will change the output voltage by .10ths of a volt, and those .10ths are what make the gauge tick up and down.

Thing is is that you seem to have too little resistance between positive and ground in your circuit. Are you using the right sending unit? There are different ones depending in if you have a gauge or an idiot light.

 

is there an adjustment on the oil pressure sending unit? Didn't see anything when installed but wasn't looking for it. Old professor had a motto above chalk board, "the only stupid question is the one not asked"

 

the shop would have checked on the gauge verses the idiot light but maybe the parts store sent the wrong one?