I have a 97 cummins that has been running really well until recently - on the flat and up hills it pulls like it is supposed to. It recently started acting up after coming down hills, particularly when pulling the trailer with no throttle and using the engine/trans to keep lower speed. Once I ge to the bottom of the hill and start to throttle, it has no power - cuts out & smokes profusely. After giving it light throttle for awhile, it clears itself up and is running great again. I have replaced the lift pump and overflow valve this week and it did not fix the problem.

 

im assuming its a manual truck right? what are the modifications done to the truck? i haven't heard of anything like that. Makes me think something might be wrong with the pump

 

Good morning - yes, it is a manual and no modifications have been done on it. Would the pump allow the cylinders to flood coming down hills? It runs perfect under a load on the flat and up hills.

 

it might i dont know a ton about them, but it sounds like your truck is creating a vacuum some how, i wonder if the injectors are worn out. That would be the first thing i would do is pull the injectors and take them to a well known diesel shop and have them inspect them, get them pop tested. I hope you have another vehicle to drive. Or if you have a buddy with a 12 valve maybe swap out the injectors and see if it happens then. That way you can at least eliminate one thing out of the puzzle. If it acts the same with different injectors, i would start suspecting the pump. I would call as many shops as you can and describe your problem. Schied diesel would probably be the first call i would make. Dynomite diesel has been good to me when i picked there brains, so i would recommend them too. There are tons of shops out there, chances are one of them has heard of a truck with your symptoms.

 

I thank you for your help - will give the shops a call.

 

I know the reason you cant put a carb on a diesel is because it will run away, obviously your trucks not running away. But i think if the needle and valve seat in the injector was worn enough it could let more fuel into the engine than it can burn. This is just a guess tho man wish i could be of more help to you

 

I have duct tape... I thank you.

 

What color is the smoke?

 

whitish gray

 

most likely your injectors are failing. i've seen this a few times