I just picked up an 03 6spd and when I shift gears the rpm hangs for a moment before dropping. I would much prefer to have the rpm drop immediately after letting off the throttle instead of momentarily hanging there before dropping. It makes it somewhat annoying and difficult to drive smoothly since I have draw out and prolong the shifts while waiting for the rpm to come down. I hope this is not normal but I have no idea what would cause this. There are no codes present pertaining to any engine control functions.

Any ideas?

 

It's normal. You will get use to it.

MikeyB

 

It is caused by the pressure of the rail it lets the rpm hang intill the pressure drops some

 

Ok, well, I guess that answers that! At least I know it is supposed to be like that....but I don't like it!

Thanks guys.

 

yeah i dont like it either when i shift above 3300 it makes me wonder if is going to come down.

i guess if you shift faster you might not know its doing it

 

Do you have stock exhaust on it?? If so put a performance muffler on it and it will reduce the hang or straight pipe it and it will eliminate it completely.

 

The higher the rpm's at the time of your shift, the longer the 'hang' duration time. Your turbo actually contributes more to this, it IS spinning and creating a pressure that has to be relieved via the exhaust system. Lessing the back pressure of the exhaust system will decrease the duration, shifting at lesser rpm's will also.

In any event, you will get used to it happening. Nature of the design of a turbo diesel. A turbo gass enegine does the same thing only it's duration seems shorter, but then their fuel rail in most instances is not at the pressure ours fuel rail runs. The rpm's are kept higher due to combustion in the cylinders of the fuel, higher pressure equals more combustion until the pressure drops.

CD

 

Yup. You will learn to shift just a bit sooner and it will stop happening....

 

I'm not following these explanations of why the hang happens. Regardless of fuel pressure, no fuel will enter the cylinder unless the injectors let it pass. I can see how a leaky injector may cause a (stumbling, smoky) hang, but rail pressure alone doesn't mean hang unless the fuel is getting injected into the cylinder.

Also, boost shouldn't be a reason for hang either. If the throttle is released, the wastegate should open and relieve the boost pressure - the air doesn't have to cycle through the exhaust system.

I would think a hang indicates a fueling malfunction of some kind.

 

FWIW, I agree....my 98.5 didn't have any issues with the rpm hanging regardless of the rpm, exhaust or fueling. There wasn't a rail but if the injector doesn't inject fuel, it shouldn't hang regardless of rail pressure, no?

 

Ah, but fuel is injected into the cylinder even though APPS voltage drops. There is a ramp down algorithm that is used. Even though the injectors are electronically fired the fuel control from the rail is still mechanical. Chopping injection immediately would cause rail pressures to spike very high. The rail return cannot bypass enough fuel to bleed the pressure off so a ramp down has to be used to keep rail pressure under control until the FCA can regulate the fuel delivery.

 

Yeah. What he said... The rpms stay high but the boost drops when this happens. It is strange but mine has done it since new.....

 

One time when i dynoed i took it to redline line let off the fuel put it in nuetral and it stayed up there i dident know what to do i just sat there lookin at it and than turned it off and it was fine??????

 

Mine doesn't do it unless i have my puck on. It really hangs when its on. Just shove it in another gear and go on.

 

Cool, thanks for that answer.

Is the ECU programmed like that for automatics also? I've never had a hang with mine.