I noticed that if I floor it and it shift from 1-2 right when it shift the engine gets much louder. Is that bad? Hopefully it's normal..

Thanks.

If your RPMs exceed around 2600, the pilot injection turns off and your truck will sound more like a traditional diesel sound. This might be what you're hearing.

I just did a search on pilot injection.. interesting..
I'm not 100% sure what RPM I heard it at but I only heard it maybe twice.
But I've probably only got the RPM's up that high twice.. So, next ride I'll see if I can consistantly reproduce it.. If so then I guess that would be it.

And that's exactly what it sounds like.. A traditional diesel. Thought I had a PSD.:eek:

I have heard the same thing on my 02' LB7.
So far so good.

If you want to force it to shut off the pilot injection to compare the sound to what you've heard, you can just select 3rd on the gear indicator and run it up to speed...it will make some noise for ya!

If you want to force it to shut off the pilot injection to compare the sound to what you've heard, you can just select 3rd on the gear indicator and run it up to speed...it will make some noise for ya!
I did just that.. That's the sound.. Does it every time. Thanks guys.

A customer who requests the fifth gear inhibit switch must understand fueling systems of diesels and the resulting noise that may be heard. This noise might be objectionable to some drivers. The following is provided in an attempt to enlighten the driver/operator of the vehicle.


Diesel engine fuel injection systems that use a common rail system, as the Duramax™ diesel does, may or may not have what is referred to as pilot fuel injection at the lower engine speeds. Pilot fuel injection is defined as a pre-injection of a small quantity of fuel 5 to 20 crankshaft degrees before the main fuel injection. This pre-injection softens the main injection pressure rise and reduces combustion noise. At engine speeds above 2600 RPM, and a fuel quantity supply greater than 35 cu mm, it is necessary to eliminate pilot injection to meet emission requirements. When driving at or above these speeds, main injection combustion noise may be noticeable. It is normal and not harmful to the engine.


When traveling in 5th gear, the pilot injection to main injection transition is typically in the 136 km/h (85 mph) range, however it may also be heard under heavy acceleration and when pulling loads up a hill during shifts at or above 2600 RPM. Customers that install the fifth gear inhibit switch may encounter the fuel knocking of main fuel injection at speeds around 107 km/h (67 mph) in fourth gear between 2600 and 2700 RPM. This sound is considered normal and is to be expected.

Found @ http://dieselplace.com/forum/forum_...sp?TID=754&PN=2

I've had 2 duramaxes now, and never could figure out what that noise was, THANKS!!!!

As a side note, I notice an increase of about 3 mpg at 87 mph as compared to 82-83, I guess this is because the pilot is off and injecting less total fuel. I've gotten used to running at this speed and averaging about 15 mpg with the AC off, as compared to the normal 12 mpg at 70 mph w/ AC off.

Are there any downsides to pilot injection? Loss in MPG? Power? Just curious.