Engine rattle
 

07.5 6.7, 100k miles, mini maxx and full deletes.

When I stomp on it, it jumps up like it ought to, but when I get around 2000rpm, the engine tone changes to something like an old International rattle for a second or two, then smoothes back out. It doesn't do it under normal operation, only when I romp on it.

The first time it ever did it was right before I did all my deletes. My cat and DPF clogged and I drove home about 10 miles in regen mode. I had to lay into it to get it to move from a stop, and it had that old International rattle.


Any ideas what might be the cause?

So when you are in regen mode Cummins uses the fuel injectors to act as hydrocarbon injectors to create the chemical reaction the DOC to create heat to perform a regen on the dpf. There are several injections going on during the cylinder compression and power cycle. Up to 2 different injections when not in regen and up to 4 on a regen situation. But also their is a load difference in the injection cycle so when you command a max load condition you may hear a tone change or a different fuel knock. Also the injector electric solenoid can be audible under a high demand.

Thanks man. I had some idea about Regen but I need to do more research to know exactly what all is going on.

If I were to take a line pressure reading when my truck does this, would you be able to say more surely that it's something in fuel delivery? I run right at 60# at idle and about 125# at steady throttle, not stomped.

Also it doesn't do that rattle if I rev it in Park, only when there's a load on the engine

A fuel pressure reading wont do much to tell you the duty cycle of the injectors. A engine load at park is much different than a engine load in drive in park you are not pushing a 10,000 pound truck, so fuel delivery and timing has change, and it is constantly changeing,