Oil Pressure Goes to Zero!

[wanderinthru]

With the state of most of these old trucks wiring, it's almost always a wiring issue.

With the location of your sender, I'd be looking real closely at where that wire runs in relation to your drivers side exhaust manifold/header.

Or one iddy biddy mouse with real sharp teeth.

 

[Bextreme04]

Or one iddy biddy mouse with real sharp teeth.

Oh man, we have ground squirrels around here that will get into cars that sit too long. I have a couple good mouser cats that keep the rodent population somewhat at bay

 

[ballencd]

Yes, gauge is electric. Caveat of the broken or shorted wire is that they are all new, have been inspected and look good. No evidence of mice or rats. Not near the exhaust as it is several inches away at the filter and in convoluted tubing. There is also the issue that it only does this when it is hot. Cold engine is normal and pressure does not drop.

You must be registered for see images attach

I'm still looking! Thanks for input so far.

 

[ballencd]

The rats used to chew up everything but we have two cats that keep them away now. I have not seen a mouse or rat for several years.

 

[deerejohn]

has anybody mentioned a faulty sending unit? i know its new but i bought a new delco oil sending unit worked for 2 weeks than nothing. replaced with another delco and been fine.

 

[ballencd]

Would that fail only when the engine is warm and its revved up in REVERSE with the brake on? Wouldn't it fail all the time it was warm and revved up....FORWARD or REVERSE or NEUTRAL.....? I think I can test it via resistance sending unit to ground and it should fail if that's what it is but I can't see it being that. Baby steps though on this one.

I am in semi-agreement that it could be a loose or grounding wire but why only in reverse and when hot......The shifter assembly is not near the wires at all.....and a short somewhere would, I think, fail in all gears.

 

[Bextreme04]

Would that fail only when the engine is warm and its revved up in REVERSE with the brake on? Wouldn't it fail all the time it was warm and revved up....FORWARD or REVERSE or NEUTRAL.....? I think I can test it via resistance sending unit to ground and it should fail if that's what it is but I can't see it being that. Baby steps though on this one.

I am in semi-agreement that it could be a loose or grounding wire but why only in reverse and when hot......The shifter assembly is not near the wires at all.....and a short somewhere would, I think, fail in all gears.

Could be a loose or damaged wire/part in the sender or harness that is losing connection only under a certain resonance that you just happen to hit in that condition. Heat makes things expand and changes clearances. Reverse twists the engine in the opposite direction from drive, so things that aren't touching in neutral and drive will be touching in reverse and vise versa. You keep going back to the wiring all being in loom, but that isn't a plus in my experience. I've seen plenty of harnesses that looked great, but once you pull the wires out of all that loom, you find they have been pinched or melted or something similar that can't be seen because the loom blocks it.

 

[wanderinthru]

Just woke up and thought of this. What do the other gauges do? When the oil pressure drops. It could just be a ground. Electrical problem and we are 2 pages in and first mention of a ground. But, there were labatory dicks swinging around and laws being written.
What do the other gauges do?

 

[ballencd]

All other gauges work fine, no changes.

 

[BillK]

The simple way to figure out the problem is to put a mechanical gauge on it. That will tell you for sure and you can trouble shoot from that point. I am in agreement with the others that it is 99% certainly an electrical problem and it might not even be in the wires at the gauge or sending unit.

But the first thing you need to do is verify the actual oil pressure with a mechanical gauge. If you are not willing to do that then you will just keep guessing until you stumble across the problem.

 

[ballencd]

That means I have to buy a new gauge. I have another electrical gauge that I could try which I can connect directly to the battery and remove a wiring issue. I will start there.

 

[R Carnella]

I sense a ground problem also check motor mounts

 

[ali_c20]

I would buy a new sending unit and if the new sending unit acts the same way it's an electrical problem with wiring and you have a spare sending unit. If everything works it was a faulty sending unit. Wires can break in the insulation and it's hard to find that wires. just m $0.02

 

[Turbo4whl]

Just woke up and thought of this. What do the other gauges do? When the oil pressure drops. It could just be a ground. Electrical problem and we are 2 pages in and first mention of a ground. But, there were labatory dicks swinging around and laws being written.
What do the other gauges do?

 

[Dave M]

Yes, gauge is electric. Caveat of the broken or shorted wire is that they are all new, have been inspected and look good. No evidence of mice or rats. Not near the exhaust as it is several inches away at the filter and in convoluted tubing. There is also the issue that it only does this when it is hot. Cold engine is normal and pressure does not drop.

You must be registered for see images attach

I'm still looking! Thanks for input so far.

Is that the transmission selector rod that is dragging across the pressure sensor cable ? Perhaps re route the wire to eliminate any mechanical interference, it may be pulling on the wire, which is causing a **** connection.