HELP! Engine hesitates under hard acceleration

[Ross]

Help. This is not in the 911 forum because I am not stranded. The truck still starts and runs, but something's not right.



Here's the deal: Under HARD acceleration (floor-boarded), the truck takes off like always, and then after about 2-3 seconds, falls on its face, puffs white/grey smoke and the rpms fall to about 1200... feels like it runs out of fuel. The truck is stock with no fueling mods. If you back out of the throttle, it will "catch up" and run ok, until you romp on it again. When the truck stumbles, the engine rattle changes its cadence, and it sounds pretty bad... lots of rattle. I immediiately changed the fuel filter, but didn't help the symptoms...



This is my wife's truck, and she drives it like a baby. No telling how long this problem has existed, since she would never notice as she doesn't put the pedal down. Problem is, she is scheduled to leave town tomorrow on about a 800 mile trip, and I'm afraid to let her take the truck for fear of her getting stranded.



Truck is a 2006 QC 2500 Auto; 70K miles.



Any suggestions?

 

[foolkiller]

i think you need to borrow a rail pressure gauge and a fuel pressure gauge from someone to check for fuel delivery problems... . probably going to need to check pressure at both the rail and before the injection pump to learn anything.



sounds like your lift pump or your injection pump isn't keeping up. research FCA as well... i'm not sure what that messes up.



also, could a TPS problem cause this?



good luck, j

 

[foolkiller]

doesn't sound like FCA from threads here.

 

[DBraunig]

Better check the air filter



Dave

 

[Ross]

I've checked the obvious culprits: fuel filter, air filter, intercooler boots, etc. Still have the problem.



Just tonight, I removed the line from the fuel rail relief valve, and started the truck. Fuel ran out on the ground in a pretty strong dribble. I feel fairly sure this is the problem, but not positive. The vehicle starts ok, but not as quick as my other 2006. It does smoke pretty good (black) when you romp on it, and then poof! it falls on its face...



My question now is, if the relief valve is bad, does it hurt to drive the truck? My wife really needs it for about a 4 day trip, and there's no way to get it in the shop and get it replaced, if that's really the problem.



The only reason I think it may be ok to drive it another thousand miles or so is that this problem may have existed for weeks or months. She never romps on it. She drives it like a baby. I drove it to work yesterday and was having some fun and laid into the throttle really hard and poof! there went all the power. No telling how long it's been this way; she'd never notice the way she drives.



Opinions?

 

[Msilbernagel]

I'm a recovering rail relief valve man... ; ' ) It ran that way for quite a while, becoming progressively harder to start until I was finally able to get some help to figure it out. I don't think it'll hurt the truck immediately but fuel starvation can be a problem as it lubricates and cools the CP3. The smoking is probably an indication of a poor spray pattern as the pressure dies off under load - not maintaining rail pressure as it bleeds back into the return. In addition, that heated fuel from the rail is now returning to the tank and heating it much faster, don't let it run low on fuel that way as excessive heat combined with aeration (cavitation) may accelerate wear in both the injectors and CP3... Lastly, mine degraded over time, eventually not starting without a shot of ether (!). So... keep the tank full, have her drive it modestly, and fix that puppy as soon as you can.

Mark

 

[Ross]

Thanks, Mark. That's the information I have been looking for. It all makes sense. It must be leaking (minor) under most circumstances, and then when the pressure climbs under a hard pull, the thing pops off, dumping everything and causing the truck to fall on its face.



The truck is under warranty, but going to the dealer is worse than going to the dentist... I may fix it on my own dime. There is a source for good condition take-off valves by a company that modifies them for high performance applications. I may get one of those and put it in.



Thank again Mark (and the rest of the TDR).



(I'll post back next week after I replace the valve. )