Just bought this truck about a month ago, recieved with trans and T case in the bed, this past week I got the rebuilt trans back under the truck where it belongs, and heard the motor (318) run for the 1st time since I trailered it home.
Engine is very quiet and smooth when it is running, absolutely no ticks/rattles/knocks.
as title says, oil pressure gauge is dead. (so is gas gauge, but I don't think that is related) Temp and volt gauge work as does tach, and rest of lights/gauges.
Unless gas gauge not working is somehow tied to the dead OP gauge, I am not gonna worry about that right at this moment, just the OP gauge. gas gauge another issue for another day.
This is my 5th square body Dakota and I have become quite used to using my trip meter as my gas gauge, ha ha, but this is 1st one with dead OP gauge.

Upon bolting up the trans, I noticed the old sending unit had been a leaker. Thru the top of the unit and into the pigtail, soaked.

I drained the oil and put new 10w40 into it and a new filter (filter had to be off to get that last bolt into the tranny, anyways, on that side)

After discovering the dead oil gauge, I plugged a manual OP gauge directly into the sending unit port and if anything, the oil pressure is high. I did not let the motor fully warm up, but stone cold, at idle I have nearly 90PSI/ and fast idle, I had around 115 PSI. I have used this gauge many times before and have checked it against other ones so I don't have any reason at this time to doubt its accuracy. I am wondering if my pressure relief may be sticking shut (but that's an issue for another day and another topic heading) truck has been in the garage for a couple of weeks now, temp in garage when I did OP test was about 55*F within garage.

AT THE MOMENT, I am only concerned about the dead OP gauge.
there are 2 pins on the gauge and the pigtail. Can I test these with a multi meter, and what results should I have on both the sending unit itself, and the pigtail/ and under what conditions?

96 is obd-2 correct? The gauge is just an on-off switch and the computer swings the needle based on an algorithm. So one side should have voltage. Probably 5 volts like the rest of the sensors. The other side will ground to the PCM.

I wonder if the excessive pressure is somehow messing with the sender and preventing the switch from closing. Like if it's a shuttle valve and it's pushing too far?

I'd think that if that were the case that it would at least blip and start to move until the oil pressure rose beyond a certain point as the engine picked up revs upon being started. It does nothing. I am wondering about 2 things/ either a defective oil sending unit even though it is brand new or else something screwy with the pigtail itself because of it being soaked in oil making it lose contact? I did spray it out with brake cleaner.

ok I had other reason to be in the junkyard this morning, cut a couple of pigtails off of junkyard refugees while I was there..... don't take much to cut, strip, solder and heat shrink, and $0 spent... we shall see.....

Except you said you had 90 psi at idle. That's already higher than it should ever be, and may be more than the sender can handle

Hope you don't blow apart the oil filter at 3,000 RPM.

yeah... but it takes a few seconds to get from 0 as in not running, up to that 90.... so that's why I thought (maybe wrongly) that I might at least get a blip immediately upon startup before it gets to that level....
being as how I just got this thing and just got it running for the 1st time since bringing it home, and changed the oil before I ever heard it run for that 1st time, I'm thinking that I should put some seafoam in or maybe dump like 1/2 of the oil and top off with kerosene and warm up, then change again to free up the pressure relief... but unless the high manual gauge reading is as you suggest, the reason that my gauge isn't reading, I'm trying to address that as a seperate issue at the moment.
so far I have fully warmed the engine up while sitting in the garage, twice since I have had the trans back in, (before I realized that my oil pressure is that high!) and started it for a couple minutes and shut it off here or there maybe 4-5 times. I have a Hastings filter on there hopefully better rep than Fram has now a days..... had a Wix on it from the PO.

I have the interior out at the moment, replacing the seat belts that the PO cut before I ever got the truck, also installed the NOS bottom driver side seat cover that I recently found on EPay, and replacing the headliner, tomorrow is the day that I will put that all back in,and take the truck out on its maiden voyage, I will probably put that manual gauge back in place of the sending unit for that maiden ride and monitor that, as well as verifying that the fresh trans works as it should....
down the road, I'd like to find a gauge pillar pod that will fit this series of truck if possible so I can add a mechanical oil pressure gauge T'd into the block and still run the factory gauge as well.....

OK/ working backwards from sending unit (because it was brand new) I did find a pinch in wires about 10" back from sending unit;probabl=y did that during trans swap, cut that out and soldered/heat shrinked back together/ no dice. swapped dash gauge with known good one out of another cluster i have; still no go.
(doing everything but another sending unit because I have stuff layin around (Cost $0) and giving a brand new part the benefit of the doubt.
so I then swapped sending units between my 92 and 96 Dakotas, (both 318s) and broke the one taking it out of the 92 so I could not try taht one in the 96, but the brand new one that I had just put in to the 96 did NOT work in the 92 either, the 92 was working fine before I broke the sending unit that came from it, as does the new replacement that I went and bought for the 92, so that proves that (at least) the new sending unit that I bought for the 96 is bad.

By 96, Mopar was suggesting 5w30 oil in most of their vehicles, with you running 10w40, that could be the reason for your higher then expected oil pressure. These new motors have tighter clearances then the old stuff had, and if it was well cared for, it could be in great condition, they wouldn't go 300,000 miles if they weren't well built to begin with.

It sounds to me like you got another junk new part, this time an oil pressure sending unit. It seems to be more the normal these days rather then the exception. Not that it would probably matter, but where did you get the new op sending unit from?

I also believe you need to be sure there is voltage to the oil pressure gauge, its possible the op and gas gauge side of the printed circuit board on the instrument cluster is defective, it wouldn't be the 1st one I've seen that was.

As far as the high op causing an issue with the gauge, I don't see how that could happen. The gauge is a simple electric meter. It measures the resistance between the power source and the ground. If the power source has the correct starting voltage, the most the gauge can read is no resistance, which would be max (or no) pressure reading. The power from the gauge grounds through the sending unit, which is a simple spring loaded resistor. The high pressure under the spring either eliminates (or nearly eliminates) the resistance to ground, or it creates the maximum (or near maximum) resistance to ground, depending on how the system is set up. Gene

another new sending unit and the gauge now works.... what ever happened to QC?

It went away when we demanded stuff for the very lowest price.
We have already felt the job loss effect of "the lowest price" when companies had to seek lower wage locations to reduce the price of goods.

Another causality of "The lowest price" we are just beginning to see is the loss of is research and development funding. I believe it will be a couple of years before we will feel the full brunt of that causality.

The next thing we will experience will be the price increase of those low priced items. Manufacturing costs have continued to rise, and a price adjustment is inevitable.

Only after people become so upset with the poor quality of "the lowest price" will we begin to see quality improve, but unfortunately I suspect that won't take place until after the low priced has that dramatic price increase. Gene

But if the higher quality item rises and the lower quality item rises equally....then most people just write it up to general price increases across the board...and that's as far as It goes and life continues...

That would be assuming that higher quality parts are still available for a particular item, and those higher quality parts can be identified. Things like op sending units only have a few options, and there are probably only one or two manufacturers. They are competing to provide the lowest possible price, and that price keeps increasing. Until people get fed up with poor quality, and demand quality parts, we all are stuck with what we thought we wanted. Gene