CVR_Rally

Some of you may have seen this on Facebook but here is the dilemma.

A few weeks ago I happened to look down and noticed my oil pressure gauge bouncing between an actual reading and being pegged. Eventually it stayed pegged whether or not the engine was running but as long as the ignition was on the gauge was pegged just like when you have the wires reversed.

1. I replaced with a Beck and it worked for a second and failed.
2. I replaced with a good used factory and it worked for a second then failed with some bouncing. It registered zero with ignition on till I started the car.
3. In both cases I can ground the wire and get a zero reading.
4. Oddly the Low Oil Pressure warning light works as expected.
5. I replaced both terminals to alleviate bad connectors.

Is this a case of over Pressure? I drive the car a lot and haven't had any other issues oil related.

MAGK944

If it's pegging intermittently it means you are getting an occasional high resistance, that can be caused by two things. The blue/white wire from the oil pressure sensor is going open circuit or the oil pressure sensor itself is going open circuit. A short circuit (low resistance) will make it read "0". If you have replaced the sensor and the problem remains it's likely the wire is damaged causing it to show high (infinity) resistance, which will peg the gauge. It will be the blue/white wire on the sensor, the one going to the terminal marked "G".

CVR_Rally

Right one would think that but the fact that they work for an instant every time I replace the sender is leading me to believe the OPRV is stuck and over pressurizing the system. Every test of the Blu/Wht I've done indicates a working connection.

I plan tonight to take the valve out (I've had it out last year to change the seal) and put it in my sonic cleaner and test it with some compressed air. I will also test the gauge with a variable pot.

Chris

spacedoc

When you remove the senders, test the resistance between the terminal and the case. If it's not infinity, then you haven't ruined the sender. I think Clark's Garage has expected resistance values.

I would think if your pressure is high enough to blow out a sender at idle, you'd also be blowing seals/gaskets in the engine.

If there's an intermittent break in the wiring, just moving it around while installing a new unit may close the circuit so that the gauge works when starting the engine, but then vibrations open the circuit again.

Good idea to test the cluster as well.

Van

Are you using a metal sealing gasket or an o-ring, or any kind of thread sealer? Perhaps the gauge housing is losing its ground?

CVR_Rally

Well folks I have at least figured out what is happening and that's 1/2 the battle. I'm actually frying the gauge itself. I figured this out after taking one apart to look inside. I see the wiper and the lead going to it but it was burnt. Hmm... I then set up a test POT like in Clarks garage. It began to smoke. Then I looked at the sender I took apart again...wires burnt...hard to see but it's toast. I could work the plunger and the diaphragm from a bad one was in perfect shape.

I had one left over sender that was dented but I could use for this purpose.
I installed it, fired up the car and again it worked for a moment then died. I did do this before the disassembly mentioned above.

So now, I have looked over the wiring diagram and there isn't really much going on from the G terminal to the instrument cluster. It looks like a straight shot. Could this really be a shorted gauge that's causing an over voltage to the sender? Needless to say I have a unique one here.

MAGK944

Just to eliminate or prove that wire, how hard would it be to run a temporary wire from the G terminal to the instrument cluster?

Don't follow the loom or anything neat like that, simply hook it up at the sensor and the cluster. If you disconnect the original G wire at the sensor you could tap the temporary wire into it very close to the cluster so you are not disturbing or removing any connector pins. Worth a go imo if you happen to have some spare wire lying around. Otherwise try bypassing that wire by fitting a temporary pot between the cluster terminal and ground to check the gauge and confirm the wiring fault.

CVR_Rally

New question:

Does anyone know what voltage if any I should have on the BL/WT wire? It currently reads 11v with ignition on. I am wondering if it isn't supposed to have any.
Thanks,
Chris

CVR_Rally

Minor update. I traced back the BL/WT wire to a gray where I thought it was having issues. I fixed it and installed a new sender. Once again as soon as you got to start the car it fried the sender. You can tell this is happening by at first it reads 0 as expected but turn the key a little further and it pegs.

At this point I need to pull the cluster and run a wire directly to the G. If it fries again or makes the POT smoke then I have to have a bad gauge.

Question: is there any relation to the ignition switch possibly being faulty? Everything else seems to work as expected.

CVR_Rally

For a brief moment yesterday when I started it up the Oil Pressure Gauge was working! At least I have some sort of conformation that it is a connection issue now and no longer cooking.

I haven't had time to run new leads but last I checked I was getting ground between the G terminal and the chassis at least. I am pulling it into the garage this week to begin a bunch of work before the next AutoX and fixing this is part of that.

Chris

CVR_Rally

Minor update, pull up the Central Electric. O plug Pin 45 leads to the G terminal on the Sender. I have resistance so that lead is good. N Plug Pin 11 has no resistance to ground. Looks like the fault is between the Central Electric and the cluster. Next step is to pull cluster.

CVR_Rally

Today's minor update.

I finally got a 500 ohm pot and was able to test the gauge. It is working properly. I tested it with the lead at the sender to make sure there were no breaks.

I'm really at a loss. I have resistance between the G terminal and ground but as soon as the car starts I get a negative reading so I'm guessing that's because voltage appears.

I had tried a factory sender and it died immediately too so I'm really stumped as to what is causing the problem. Note: Whenever I install a working sender it works until I start the car (once it starts seeing pressure)

951Dreams

Since the pot works, maybe it's getting bad voltage from the system?? Is it just 12v? If so I'd run a straight wire to power side and see what happens...

marc abrams

First you need to establish a baseline to what kind of amperage flows through these sending units because I have no idea. You have two other gauges that work, temperature and fuel gauge. So let's use them. Disconnect both the temperature and fuel sending units. With a ampmeter in series from ground to the sending unit wire measure the amperage. Then do the same with the oil sender. I'm going to guess you are going to see a higher amperage on the oil pressure circuit cause by the oil pressure gauge itself. So you don't fry another oil sending unit, try installing a inline fuse on the oil sending unit until you find the problem. And besure that you have the correct fuse in the gauge circuit before you start testing.

Jfrahm

Good advice. I'm wondering if something is not grounding through that sender, I am not sure how else you'd fry the poor thing.