89dieselkong

Well, the truck was suffering from some intermitent hard start issues, where it would crank over and not start, and then the next turn of the key would start fine. Well today while accelerating from a stoplight the truck stumbled on itself and almost died. I let of the pedal and it caught itself, then tried to accelerate again and it did the same thing, with a lack of power. Got on to the side of the road and it idled fine. Got back on the road to go home and it runs fine at low speed, light acceleration, but any extra push on the pedal (even minimal) results in the low power/stumbling. Truck made it home 7 miles without incident.

Here is what I have:
Filters just changed less than 1000 miles ago.
Engine was rebuilt by PO 40,000 miles ago
Not sure if CP3 pump is original or not
Not sure if lift pump is original or not
Injectors are new Scheid units with 5000 miles on them.

Whaddya all think?

jhenson

Have you verified the LP is working? Sounds like a lack of fuel to me.

Hummin Cummins

I'm still thinking fuel rail pressure is low

Lift pump is easy to check. Remove filter, put in new filter, put on lid, turn on key until stops, turn off key, remove fuel cover lid. See if fuel in bowl.

It could be the high pressure pump but unlikely....with the mods it's difficult to rule it or any mod out

Sounds like low fuel pressure or availability (clogged filter/bad pump), air in fuel, bad ground on an electrical supplies device (whether oe or aftermarket add).

I've heard of throttle position or crank sensors going bad too...but rarely

89dieselkong

I haven't verified the LP yet. I did just change the filters last month and it filled the bowl fine. I don't have FP/RP gauges either, so I can't use those. Although I am thinking about getting them to start there. There are a few threads that mention some wiring by the ac condenser getting worn so I am going to check those later today. You mention low rail pressure or air in the lines, aside from going through and tightening all the lines and fittings, how would I check that stuff? When the lift pumps go, do they just die all at once or intermittently? When the Walbro unit went on my last truck the fuel pressure gauge was all over the place, which is how I knew. I had the same symptoms on my last truck ('02) and it was the VP44. But I think this is different as I don' really think the CP3 is bad. I could be wrong though.

jhenson

For the most part the CP3 is either gonna work or it's not. I am "assuming" (I know, I know....) that you have a factory LP. I installed an AirDog unit on a buddies '07 and when we pulled the factory unit from the tank the screen on the LP was so stopped up that the truck wasn't getting any fuel.....it would stumble all over itself. Not saying that's your problem but it's a thought anyway. Under light throttle it did ok but once you got in the throttle the problems started. Are you getting any codes?

89dieselkong

I haven't checked for any codes yet (still at work lol) but I will this afternoon. I am guessing it is the lift pump just due to the amount of miles, 186,000 on truck with idling hours at around 500,000. I really hope it is the LP so I can replace it lol, I can drain the rails with the Jr's performance tune and my injectors now, so replacing it would be a good idea anyway. Yes it is he factory LP, just not sure if it is the original, but I think it is. The PO told me about everything that he did to the truck and never mentioned the lift pump so that is my thought.

Hummin Cummins

That's a good point. The 03 doesn't have the in tank system...03 has a frame mounted electric pump near the fuel filter

The hit/miss of the situation makes it strange. My 96 Chevy 6.5 had that problem...was the electrical connector to the standadyne pump...that's another story.

Hummin Cummins

I heard the new 6.7 pumps will pull the fuel filter apart and into the injection pump if the fuel filter is blocked...best to change fuel filter with oil changes.

gasser76

Err ... maybe you meant 5,000 hours?

89dieselkong

lol, yeah I just realized how that read. What I meant was that as far as hours on the motor, it is the equivalent of 500,000 miles or so, most of it from sitting at idle in the oil fields even though the odometer shows 186,000 miles.

I ran the codes and got nothing for the LP. Does that mean that it isn't the problem? I took it for a quick spin and at light throttle input it is fine, but any extra go and it falls flat and sputters. Once I let off the pedal it is fine, idle is fine and everything else.

Hummin Cummins

How's your turbo and boost?

...is it a complete stumble to no motor at all?
...or a lack of power but still motor pulling? If this is the case could be loss of boost through bad turbo, turbine fins, or tubing/inter cooler...

...OR fuel supply not compensating for boost levels (blocked line, filter, poor performing pump(s), stuck relief valve, or something)

...do you have loss of engine oil ? ..or any oil running forward on the pipe from the exhaust tip?

89dieselkong

I actually never keep into it long enough to see if it will die or not. It is a stumble/stutter, not a lack of power. The turbo seems fine (it is relatively new 40,000 miles on it) so I don't think that is it. No loss of oil that I notice. How would I check the relief valve? It seems to be a fuel issue, but there is no code and the LP does cycle when I turn the key, not every time, but usually. It depends on how fast I turn the key on and off. My only thought really is to get some FP/RP gauges and then see if I am losing pressure. Even though I want a new LP, $500 for a pump is hard to swallow if it isn't needed.

Hummin Cummins

Relief valve is checked while measuring common rail pressure...at same time cp3 is checked.

I know DC garage can check it. Cummins garage can't as the engine software is accessed by DC software that I know of (beyond me)

89dieselkong

Would that throw a code if pressure was off?

Hummin Cummins

When common rail pressure is tested Dodge actually load tests the engine and cycles it's abillities