I have a 2004.5 LLY with 4" Magnaflow from the downpipe back with no kitty, J/A on level 2, all the time. I have noticed that after semi-hard to hard acceleration the engine will rattle or kind of knock (like a gasser running on crappy octane) what is wrong and how can I fix this. It seems to have no loss of power at all but it sounds like Censored . :help: Also, I have tried to play around with the J/A levels in the past but it seemed to do the same thing.

you are getting to the point in the tune where the pilot injection is turning off. no need to be quiet when you are on that pedal, so the pilot ínjection shuts down..... completely normal

It happens after I am out of the pedal, like off the line to 50 to 75 mph, let off the pedal a little bit and then the knock/rattle. It sure sounds bad, almost like it is running out of fuel.

It is a rather odd sound... many other people have comented on this and even been scared of it untill they learn that its perfectly normal.

Are you the original owner? If so, has the GM computer been reflashed with the GM upgrade that came out last September? The updated GM program should reduce the rattle.

Also, what version of the Edge do you have? The most current for the LLY is 1.2 and came out in March. Edge will do a software and hardware update for no charge.

There are older posts on this site saying the software upgrade has reduced the rattle. I would suggest that you update the GM and Edge software if this has not been done already.

I am the original owner and no GM reflash has been done, however the edge is the 1.2 version. I will go and see my dealer and see if that helps. thanks for the help.

JW .... Read post number 16, posted 9/13/04, by dmaxalliTech (Eric). It is the original annoucement of the software upgrade. (I think there have been a couple of minor revisions to the original annoucement.)

http://dieselplace.com/forum/showthread.php?t=14522&page=2&pp=10&highlight=pip3129

You can also do a search on "PIP3129" and find many references to the upgrade.

Some dealers have been real good about providing the upgrade and other have been a real pain. It is best to use the same terminology in bulletin when describing the problem to the dealer. You might also want to say it is intermitent since some might want to test drive the truck first. Hopefully you have a good dealer. If not, go to the next one. Be sure the Edge/Attitude is out of the truck before driving on the dealer's lot.