OK, long story short.

I went out the other day to start the truck, been sitting for a couple of weeks, checked the oil, right on the full mark.

Crawl in fire it up, no oil pressure, shut it down pulled the plug out of the top of the filter housing hooked up my mechanical gauge and started it up, 75 psi at the filter head.

Fast forward to today, got a new sending unit from Cummins, installed it and now it reads just under 40 PSI while the mech. gauge at the filter reads 75.

I don't get it, engine sounds fine, no smoke or anything else odd.

Any ideas?

 

Depending where the electric gauge reads, it could be down stream of a few passages that could restrict the flow. Thus causing less pressure. Mains, con-rods, anything like that. Maximum pressure would most likely be at the filter. I believe the oil goes pan, pump, filter, then onto the engine. I'll look at my manual to see where the sensor is located.

 

The one thing that gets me is when I parked it I had 60+ psi at idle, no noise or anything funny, start it 2 weeks later and now I have no oil pressure?

Sensor is located behind the ECM on the drivers side of the block.

 

The oil pressure drop makes sense to me. Loss of flow through the passages between oil filter housing and the sensor. It is very funny that in two weeks the sensor decided to give up the ghost.

 

That's what I find odd, I got the Cummins #4921511 sensor, I work with this parts guy directly all the time so I trust him.

Tomorrow I am going to adapt my mechanical gauge to go in the factory O/P port and see what it says.

Thanks for the help.

 

Good call, that is what I do when diagnosing a machine. Ours are usually 1/8" NPT. so I have a running T that the factory gauge can be put in, and another for my test hose and mechanical gauge. It will be interesting so hear of the results.

 

Lil' update: pulled the sender, installed mechanical gauge in that spot, started the truck, 75 psi at the port.

Re-installed the old sender (cause it's so fun to get to), no reading at all, Re-installed new sender no reading at first start, shut down wait 5 mins. re-start gauge reads just under 40psi so far.

And that's where I am at, not sure what to do now.

At least I know the engine isn't being damaged by low oil pressure, just frustrates me to no end that I have a gauge that doesn't work correctly.

 

Almost sounds like its a wiring issue now. That's rather odd that a new sensor doesn't read properly.
Just had a look at my truck as I have it in the shop now. That is a bugger of a place. Not too sure which would be worse, oil pressure sender, or MAT. I just cleaned my MAT, its a bit of a bugger to get to.

 

Got it, the only thing I can think of is that the new sensor had an air lock or something, reads fine now.

I remember looking in the sensor when I pulled it back out and thinking it was a little odd not to have oil in it after running but that's as far as I thought about it.

Now it is as accurate as it has ever been reads real close to my mechanical test gauge.