"Fuel Piloting" - fact or ficton?

[Pingmister]

I took my 04. 5 with 2K miles to the dealer after noticing a "clicking" sound very similar to rocker arm noise or spark knock. The clicking was noticeable only while hot and a load was placed on the engine, i. e. acceleration or climbing. They were stumped and after calling several sources and adjusting the valves they asked me to bring the truck back so that a Cummins Rep could be consulted. After the second visit, I was told the "clicking" was normal for later versions of the 04. 5 since Cummins added a feature called "fuel piloting" to automatically adjust the fuel mixture. The service rep told me he'd driven a new vehicle as a test and noticed the same sound. They also said the isolation test for injectors I requsted produced normal results. I'm not complaining about the noise but want to know if damage to the hardware is being done. Thought I'd ask the real experts if they knew or heard about "fuel piloting. "

 

[Big_Daddy_T]

What we call it is pilot injection. Yes an 04. 5 will have pilot injection. Not sure about the noise being related.

 

[rbattelle]

They may be trying to describe (in very odd terms) the effect of pilot injection turning on and off.



Pilot injection is when you squirt a small amount of fuel into the cylinder a little before the main fuel charge. The effect is a heating of the combustion chamber in preparation for the main charge, which causes a more complete burn of that main charge (and significantly reduced noise too). Under various sensor conditions, the feature turns on and off, resulting in a noticeable change in engine noise (possibly including a knock or clicking sound).



For those more technical minded, pilot injection is a catch-22. Although it results in a nice warm combustion chamber for the main charge, it consumes some of the available oxygen in the chamber. As a result, if it's not designed just right you actually end up with a poorer fuel burn in the main charge. To avoid this, the designers have to provide additional air to the chamber when pilot is in effect, or strike just the right balance between pilot quantity and main charge quantity for maximum effect. I suppose perhaps they simply take the main charge without pilot injection and subtract off the quantity desired for the pilot. In math terms:



Pilot Volume = (Total Desired Main Charge Without Pilot) - (Pilot Volume)



I don't know for sure if that's the way it's done, but if it were me that's where I'd start.

 

[Pingmister]

Many thanks Big Daddy T and rbattelle for the quick reply. As a novice diesel owner, I've quickly learned to appreciate the helpfulness and knowledge of TDR members. Joining TDR is one of the best investments I've ever made.



Some members reported a fix for "pinging" after installing Service Bulletin 18-037-04. See klenger's thread, https://www.turbodieselregister.com/forums/showthread.php?t=113455



Checking this stuff out is a blast!