I have a 2004 Dodge 3500 (no mods other then cold air intake) the temps here have dropped down in the teens now. My question is if I do not plug my truck in it will surge and buck like crazy untill it is at running temp, then It will also throw codes like P2121 which is the TPS. (which I replaced earlier this year also)

Can anyone tell me why? This makes no sense to me at all..

 

Rail pressure? Sounds like the FCA or rail pressure relief valve have an issue...

 

Tis the season.

 

i dont have exactly the same prob or the same temp but cold starting mine for some reason for the first 10 min or so my lights will go dim back n forth... inside and out... doesnt run bad but itll do it till it warms up..

 

That is the grid heater cycling off and on. What does your volt gauge say when the lights are dimming? May have weak batteries or some loose connections.

 

never noticed the guage moving any and i it cranks wit just a bump of the key... i havent actually put a volt meter on either one of my batteries though to see... is that normal?

 

Yes it is normal for the cycling of the grid heater when it is cold. Not really normal on the lights dimming down or at least not to me.

Mopar1973Man's Dodge Cummins Articles - Grid Heater

 

i appreciate it!! im new to the CUMMINS game but def gettin used to it and liking what im learnin... i been owning a 7.3 since i could see over the steering wheel so its all new to me... thanks for the help!

 

My lights will dim when my grid heater cycles, although im thinking the guy before me put smaller batteries in then usual the good thing is the batteries arent by any means bad they hold a great charge and the capacitor for my subs doesnt run all that much but when it does the gauge says 14.5 volts which is normal. It doesnt stall my truck out or anything quite truthfully I think ill be okay even with multiple keying cycles the battery still doesnt hesitate to turn the motor over.

 

The gauge in the dash is controlled by the ECM...it will only show what the ECM tells it to show. If you put a real gauge on it, it will bounce all over the place when the grids are cycling. Lights dimming when the grids are on is completely normal.

BTW, your cycling should stop once it reaches about 3 minutes, or you reach about 25mph...