Ok I have a wierd oil pressure problem. I have a 98 1500 3.9 v-6. At idle in park oil pressure is normal, while in drive/reverse and moving the oil pressure is normal. However at idle in drive/reverse oil pressure drops to zero with check gauge light coming on. I should say when it drops to zero is both from moving to a stop(ie stoplight) as well as when cranking the truck and placing into gear. I have replace the oil pressure sending unit with no change. Oil is within the safe zone of the dipstick.

Thanks for any help you can provide

 

Have you checked the oil pressure sensor?
It might also help to do a oil change, and maybe run some seafoam through the crankcase first to clean out all the oil passages.

 

I have replaced the oil pressure sensor with no change in results.The oil is fresh as well. I was worried about seafoam as the engine has 202000 miles on it. Wasnt sure if it would do more harm than good if the previous owner didnt maintain the engine properly.

 

What is happening is that at curb idle (neutral or park) you are sitting about 7 psi. When you put it in drive or reverse and hold the truck still it puts the motor under load and the rpm drops, causing the oil pressure to drop slightly. The oil pressure light comes on at about 5 psi. The reason the gauge is dropping to zero is the oil pressure is so low it is out of the range of the oil pressure sensor.

Its not a big deal as long as the motor runs fine and doesn't make noises. With 200K+ on the truck it has lived its life. Run it till it blows, you more than likely have many miles left to go. If you want a few more psi use a quality filter like a napa gold. I have noticed a few psi improvement by using this filter over a fram.

You may not believe me that the actual oil pressure is so low, not many people do because their factory electric gauge reads 40. If you don't believe me hook up a mechanical oil pressure gauge. It will tell you exactly what the oil pressure is. You will be suprised.

 

LOL NICE... Thanks for the help. I havent noticed any major issues. It has a miss but I think that may be plugs havent checked yet. Am replacing the transmission with a salvage one as when placed in 1st gear the vehicle bogs and will not move similar to brake standing a vehicle. Gotta love the 42RE quality NOT!!!.