I have 1999 Dodge Cummins 5.9L, between speeds of 45 – 55 mph, I can see the tach and feel the engine surging, but the speed remains steady. I have changed the Throttleposition Sensor, Transmission Solenoid and had the Valve body worked on. There is no check engine light and the only code was for the now replaced throttle poistion sensor. I am at a lost on where to go next to fix this issue. Anyone have any ideas.

 

Does it feel like the transmission is shifting back and forth trying to find the right gear? if so read this link, it's the last post.

 

https://www.dieseltruckresource.com/...q-t110571.html

 

Did you check the TPS for the correct voltage range?

 

On my 01 I had a similar issue. I could drive say a steady 65mph I could hear it though not really feel it. It has been a while and I cant remember if the tach was moving or not if it did it was very minimal. At first it only did it when it was really cold out. Then it started doing it when it was warmer and warmer. I never did figure it out. However I can say that when I replaced my vp44 it went away. It always ran fine (well until my vp really crapped out with the 216, dead pedal etc). I thought it may have been the truck havng a hard time trying to decide what timing to use as mine was a very steady every couple seconds cycle.

 

I have replaced the fuel lift pump about five years ago, would putting a FASS system to replace the lify piump work

 

Don't just throw parts at it...

Try to get a code or continue investigating it till something reasonably close gets suggested.

Start with the free stuff like cleaning all grounds and checking battery cables, etc. fuel filter/fuel pressure/blah blah blah.

Upping the fuel pressure won't repair a failing IP.

 

Thanks for all the responses, I cleaned the three ground spots and the battery terimals and it appears to be running correctly now.

 

Evans,
If cleaning the grounds fixed you up, then you are where I was a year ago. If it comes back, get a tranny noise isolator from Geno's Garage, if that fails, this oughta do it for you:


http://www.atsdiesel.com/additionali...02)%20v1.0.pdf

 

Nice work, I just saved you 2 grand! Ha ha!

glad you got it fixed!

 

Does this kind of thing affect 6 speed manual trucks as well?

Mine has what appears to be the same problem. Really bad when cold, still there but less when hot. between 1500-1800rpm it feels like it's got air in the lines but not at idle or when i'm rowing through gears. Shop threw a fuel filter and a water separator drain valve at it trying to find air gremlins...

 

I think bad grounds could also affect manuals too...it just doesn't hunt for gears(obviously)

 

cool. we'll start there

 

Well, let me rephrase this. It won't directly affect the manual transmission itself cause it doesn't electronically shift but cleaning up the grounds is always a good idea in my opinion. If cleaning up the grounds doesn't help at all I would suggest starting a new thread explaining your situation. then someone that knows a lot more than me will probably give you more help than I ever could.