Typical first post, but I'm looking for help.

'98 Dodge 4x4 with the Cummins and automatic. Mileage just over 150000 miles. The engine seems to run fine but it has very low power until it is fully warmed up, then if the RPM's drop below around 1700 the power suddenly drops dramatically and the truck slows down. I of course press the accelerator and the transmission shifts down, the RPM's come back up, and the power pops back in. It's a real pain to drive like this as you can imagine. What I'm imagining is happening is that the turbo is seizing up when the exhaust flow drops down, killing the power.

What do you think?

 

I doubt it's turbo related, but take the intake elbow off and see if theres lots of oil in the turbo, or if you can wiggle the shaft around enough for the wheels to hit the sides. The turbo should also spin freely.
Check all the simple things first, air filter, fuel filter, even the precleaner.
You may have a air leak in the fuel system somewhere, how does it start?
Your cat (if equipped) may be plugged.
Could even be trans related.
12 or 24 valve?

 

Racer, thanks for the input. It doesn't have a cat. My reasoning is that if it were an obstruction in the exhaust it would always have a loss of power instead of coming and going instantly as it does. It always cranks instantly, hot or cold, but if it's cold, even though it's running fine, if you hit the road it will sluggishly climb to around 35 to 40 mph with the accelerator floored. Then as if something kicks in, it will take off. Whatever it is will kick in and out constantly if I cruise at around 55 to 60 mph, and it's even more obvious with a modest sized trailer behind it. It doesn't use oil either if that helps.

 

24 valve or 12 valve?

 

It sounds like it might be either your TPS or TTS. How many rpm are you losing when it drops down? Does it sound like the transmission is hunting? I've got a 99 24v that does the same thing between 1700 and 1900 rpm. Its the torque converter locking and unlocking repeatedly. I bet when you accelerate straight through the trouble spot you have no issues, its only when you're holding engine speed in that range right?

 

they didnt put 12 valve in 98 and above, 97.5 is wen they started the 24 valve i believe. please correct me if im wrong.

 

1 off. They switched in mid 98. Same year they came with the quad doors.

 

ok cool, thank you, i new it was one of those, lol, thanks for that.