When I turn my key on (engine not running) my oil pressure gauge shoots up to ~40 PSI and stays there--seems to work with the engine running but I can't trust it if I'm having any sort of problem with it...any ideas on where I should start looking?

 

Your truck most likely has the factory "fix" installed.

Dodge was having repeated problems with oil pressure senders failing because they are cheap and the Cummins hammers senders pretty badly.

After a large number of complaints of "I have no oil pressure" only to have it be the sender, Dodge decided to permanently "fix" the problem by programming the truck's PCM to ignore oil pressure sender signals under 40psi.

So basically, your gauge is not working, because the PCM is ignoring the sender's input and just slapping 40psi on the gauge regardless of what is actually happening.

I'd recommend a cheap mechanical gauge be installed if monitoring OP is that important to you. Your factory gauge is essentially useless (or worse).
As you may know, there's a 1/8" NPT oil pressure port on top of the oil filter mount-- just take out that plug and you have your oil pressure port.

jh

 

Thanks for the reply--

My oil pressure gauge has only been doing this in the past 2-3 weeks (I've had the truck for almost 4 years) so I know this isn't from the "fix" (read: band-aid) that you mentioned. I probably will install a real oil pressure gauge though. Monitoring my engine has always been a priority for me, which is why it frustrates me to no end that a high-performance vehicle like my '87 Grand National came with no real instrumentation--just an 85 mph speedometer, fuel level, and tacky LED bargraph tachometer and boost gauges which aren't accurate at all... My '86 Caprice Classic that I had years ago had better instrumentation...

 

Forgot to ask...where is the factory sending unit located anyway?

 

I think it's on the passenger side near the t-stat. I'd have to go look to be sure.

 

Mine did the exact same thing. I replaced it and it works like it should. I got my sender off a wrecked truck. Took a chance of it not working but it does and it only costs $10..i think they are around $90 from cummins and $200 from the dealer. It is located on the drivers side of the block right under the ecm i think. It is basically half way down the block (front to back) and a little lower toward the oil pan. hope this helps.

Kip

 

Sounds like the internals of the sending unit are stuck....