Thank you for all the help, I have another question. The oil guage reads 80 lbs. which is great but thats with the ignition switch in the run position with out the engine running. It stays in the same position when the engine is running. The guage does drop back to zero when I turn off the ignition. I'm thinking oil pressure sending unit? And if that is the problem is it located on the back of the block? Since I am my mechanic " hopefully not to often" is there a repair manual like chiltons that cover these trucks? Thanks all, sure appreciare the help!! Ran

When the engine warms up, is the oil pressure gauge still pegged at 80 lbs under all conditions, or do you find that once the engine has warmed up the oil pressure is lower at idle? I don't know how the '99s work, but I believe that the 3rd gens run the oil pressure reading through the computer, so the computer gives you a reading based on what it believes the oil pressure should be, rather than what it is. However, I'm guessing from what you said this is a new development which would indicate...

The sensor or the wiring to the sender. You could possibly have a short. I don't know where it's located on this motor, but someone else on the forum should. Good luck!

the 3rd gen cummins oil pressure switch is set at 6 psi. above that, normal, below that, 0psi on the gauge. but the engine will run for about 30 sec before the gauge will drop to 0psi. at start up, i instantly have oil pressure on the factory "gauge" but it takes a few seconds for pressure to build on the stand alone electric gauge i have in the cab

The guage only reads zero if the ignition is in the off position, as soon as I turn it to the run position the guage reads 80 lbs. rather the engine is running or not. I'm thinking I'll get a stand alone guage, probly cheaper then fixing the stock one. Thank you Ran Edited by: Ran

You have a bad sender it is on the drivers side of the engine block just to the rear and below the injection pump. New one at napa is around 25 bucks if I remember right vibration of the diesel is hard on these.

Thank you Elkhunter, dig your name, I'm from Missoula Mt. ,been hunting elk with bow and rifle for going on 37 years. Thanks again!! Ran