In the past 1.5 weeks I have been trying to figure out this stumble/hesitation at no to low throttle just off idle until about 1200 rpms.

What happens is that when I let out the clutch the rpms will drop down to about 700, then a bunch a light grey smoke will come out the pipe, the truck will stumble and barely pop / "poof" once out the exhaust, and then just take off as normal. Also, around idle rpms when letting out the clutch the truck knocks like an old cummins as if the pilot injection was turned off. From 1500 rpm and up it runs like a raped ape! I can duplicate the stumble between every shift if I let the rpms fall below 1500 or so. I can also duplicate the stumble if I coast to say a red light in gear, but don't down shift, and then take off when the light turns. If I take off from a stop with authority or basically hot-rod the truck, then no stumble or knock sounds whatsoever.

I also noticed lately at low boost and rpm conditions when I apply some throttle more grey smoke than black. Smoke used to be black during these conditions. It is almost as if the truck is getting lots of air, but no fuel at low rpms. Fuel pressure to the CP3 is good at 14 psi, but I changed the fuel filter just in case and it still stumbles. Mileage hasn't changed at all. Oil looks good with no fuel smell and no change in level.

So thinking this was my Juice box causing this due to its manipulation of injection timing, I traced the lines and checked the connections this morning and only found my Attitude control cable wrapped around the steering column with some bare wiring exposed (don't tie-wrap wires to the steering column!!). I then removed the Attitude letting the Juice default to level 2 and went for a ride and the truck still stumbled.

I went back home removed everything and went back to stock form, except with DD3 injectors and turbo, and the truck still stumbled!

Also, yesterday evening (with Juice still connected) I was playing around on Level 5 on the back country dirt roads and tripped my MIL light and got the code P0193 - Fuel Rail Pressure Sensor Circuit High. I used my scan tool to erase the code and it hasn't come back since.

So here I am in stock form with the truck still stumbling or hesitating at idle to low rpms with light throttle. No codes either! Otherwise, the truck runs like a scalded cat!

I am wondering if my pressure relief valve is going out? Say at idle there's minimal rail pressure, but when you give throttle the ECM asks for a major increase in rail pressure and the CP3 can't initially keep up due to the rail pressure bleeding off?

Does Cummins have a computer to hook up to our truck or this a dealer only computer? The local dealer is .... so I would like to avoid them even if it means a 240-mile drive to the next town. Or I may just have to bite the bullet...

Are there any scan tools that can measure rail pressure? I just have the AutoXray 4000 (basic version).

Any ideas are much appreciated!

 

That stinks. Have you been able to pinpoint when this stumble started happening?

There are aftermarket rail pressure gauges available - but I don't know of any places you can just go and get it scanned.

I hope you get this figured out!

 

Got it solved! This was truly an experience in Troubleshooting 101: Back to Basics

Here's the details:

http://www.turbodieselregister.com/f...d.php?t=136945

 

Plugged fuel filter or a bad lift pump.

I'll go for the pump.