Engine/Transmission (1998.5 - 2002) Low Idle Fluctuation

[CumminsFarmer]

I recently pulled the injectors on my 02 Ram, and had them hydraulic honed or "flowed" to a Phase Two setting. The power increase is great, and Ive noticed a mileage increase as well. There is however one small problem. At low idle, there is an noticeable fluctuation on the tach. of about 50 RPM or maybe a little more. The injectors check out fine, and Ive been told its not a computer issue. It didnt do it before the mod. and nobody else I know that's done the mod has this fluctuation. Anybody got any ideas?

 

[Beast2B]

Welcome to TDR! I have slightly larger injectors and get the same fluctuations, even worse with my fueling box turned up for more fuel at all boost levels. From what I've read, it's common to lose a bit of idle smoothness when using larger nozzles. Were the injectors flow tested after being honed? Are they flow matched? Possibly some slight variation between injectors could cause this in certain trucks.

 

[CumminsFarmer]

The injectors were all tested after being honed, and they checked out fine. I also was told about a slight loss of smoothness, but I think this is more than normal. A fellow mechanic told me that the fuel cross-over tubes, between the lines and the injectors can be knicked a little when re-installing, and that will cause a fluctuation. Ive considered this, but it would seem to me that one nicked line would cause a flux only on the powerstroke of that cylinder. I'll accept a little flux, but not this much.

 

[Beast2B]

Does it go away above idle? How about fuel pressure from the lift pump? If the VP is pulling all of its fuel, there may be issues. Maybe a long shot, but the APPS (accelerator pedal position sensor, i believe) can send bad signal... possibly fluctuating between idle/off-idle voltages. search apps to get a quickie calibration method.

 

[CumminsFarmer]

It does seem to go away above low idle, but thats not a guarantee. I havent been able to check pump pressure yet, but will soon. I also plan on hooking up a scan tool in the near future just to see if anything interesting pops up. I considered a timing advance by the computer for the new fuel delivery, but several others said that wasnt a possbility.

 

[R-N-R]

My truck has hunted at idle since brand new, larger injectors exaggerated the fluxuation. Some days it almost sounds like a gasser with a performance cam loping at idle.