I noticed when cruising in the low 80s (mph) and then bumping the cruise up to 85 or so after a few moments the engine would make this horrible noise, get really noisy, but for a second the power would pick up, I have read this is the pre injection turning off, is this true, simply letting off the pedal makes it go away if you are not in cruise. Still got close to 19 mph cruising at 82-3 mph for over 600 miles, so I am pretty sure it is running correctly.

Mine makes the noise to. I think it is the pre injection or injection timing change(advanced).

Pilot injection shutting off.

ditto on the pilot injection

This is a great thing to know because when I pull away from all those Fords and Dodge's going up Jelico Mountain, I will know this noise is normal. Rember men, Real Trucks Don't have Spark Plugs.... Drive ON!

pilot injection closing off

When does the Pilot Injection turn off?

Lone Ranger, I think its around 2500 rpm plus, depending on engine load. The DMax doesn't have that "rock crusher" diesel noise at idle and lower speeds because the injectors take a "double shot" of fuel. There's a short pilot injection that starts the burning process to prevent the shockwave that occurs on the main shot. When the rpms get too high, there's no time for the pilot shot and the injection has to occur as a single shot that creates the shock wave and diesel rattle.

WELL I'LL BE DAMN....YOU GUYS KNOW IT ALL... I WAS WONDERING ABOUT THAT MYSELF

WELL I'LL BE DAMN....YOU GUYS KNOW IT ALL... I WAS WONDERING ABOUT THAT MYSELF

Now all we gotta do is get GM to start listening http://www.dieselplace.com/forum/smileys/HiHi.gif