tbrave2

alright, so when i get my truck goin at about 2200-2500 rpm and go to shift i let off the throttle and hit the clutch. the only problem is that my rpm's continue to build and i cant put the truck into the next gear until the rpms drop a bunch, happends all the way threw the pattern. could anyone give me some help with this.

BigIron70

Does this happen with the cruise control switch on or off? There is a recall for ECM reflash if needed, maybe related if it applies to your truck. Read the recall to make sure if it does.

no_6_oh_no

Thats pretty normal when you are revving the engine like that. The CR's don't back off right away due to the rail pressure that needs to bleed off. You just learn to drive around it.

Have tried it with the Quad off?

tbrave2

took quad out helped with it a little but its only becuase the truck doesnt build rpms as fast and it felt alot slower and the ECM has already been reprogrammed

no_6_oh_no

Just one of the down sides of a manual trans and programmers. They are not made to shift fast.

hivoltage

I'm stock but my truck ALWAYS drops RPM's normally no matter how I drive it.
I've heard many guys say it a CR thing but I don't buy it. It may be normal for a CR with a programmer to do it, but I don't think it's a normal condition for a stock rig to "hang" just because you're pressin' hard on the skinny pedal.

no_6_oh_no

Its not from pressing hard on the skinny pedal, its from building high rail pressure and dumping the load quickly. Its normal with or without a programmer. Programmer just exagerates it with more fuel.

That being said, if your truck doesn't do it and thousands of others do where is the difference? What supply fuel pressure do you have? What rail pressure are you running at 2600 rpm's under acceleration? How soon does that rail pressure drop when you lift off the accelerator?

I would hazard a guess yours is not normal from all reports but maybe you have a special tune that addresses it.

hivoltage

Thanks for clearing that up! Let me rephrase ....it shouldn't matter if you let off of the skinny pedal real fast!
I'll say it one more time, I'M STOCK completely. I have no idea what fuel pressures are. All I know is I can run the truck clear up to redline and let off as fast as I'd like and the R's drop like normal not "hang" as the op is describing...
You can say what you want but I don't feel it's normal for a stock rig to "hang" like that.
I'm not a pro and don't have all of the answers but I've driven more than one Cummins diesel and have never had one "hang" at high rpm's....just my experience....

Spooler

Auto's will do it too if you get into the right circumstances. Say, starting off in traffic real quick and having to stop quickly because someone is an idiot.

AirGrabber

Yes this is a normal side effect of the common rails. Especially in the earier ones. They will "hover" a bit before beginning to decelerate. Every single one ive driven has acted the same. 04.5 and up are not as bad but all are noticeable. If its hovering alot more than normal and causing to many rpms to shift within a reasonable time then I would say you have an issue. apps,throttle cable, could be the culprit. Floor mats seem to be pretty good at causing this aswell.

no_6_oh_no

This may very well be a difference in driving expectations. What you feel is normal may feel like a hang to someone else.

I don't even notice it anymore as have learned to drive around it and compensate.

I do know every 3rd I have driven has done it to a certain degree, and, every 1st or 2nd gen that did it had a problem or they did not hang. The first time I whacked the throttle too hard in a parking lot I thought it was BROKE!

Ace

So are you saying the injectors are still injecting more fuel than they should be after you've let off the accelerator pedal because of high rail pressure?

no_6_oh_no

That is the crux of the matter, what is too much. Since these trucks are drive by wire there is no hard and fast rule how much should be injected with so much throttle, only a set of tables that define the relationhip between rpm's, speed, and APPS position. The little proprietary chunk of code that interprets these table has its own ideas about how some of the parameters apply and the operations work. Best guess is its a safety feature since the rail feed control is electro-mechanical and it simply takes time to process the off command to where the CP-3 quits building pressure.

If there wasn't a ramp down you would see spikes a LOT higher than they occur now and even faster injector failures.

Ace

Ah yes - the ol' translation from the digital to the analog domain...

no_6_oh_no

Yep, we call them electronic controlled but it is far from that easy. The ECU "thinks" much faster than any controls can operate. Built in time lag for translation is a big problem, both for OEM and aftermarket.