Hey guys, starting this afternoon my tranny started acting a little strange. Here is what is going on. If and when I really stand on the throttle as in push it to the floor and my rpms get to right around 2500 it is like my engine starts defueling and keeps me at and under 2500 rpms. Though if I don't punch it all the way down and just stay a little before all the way and ease my way to those rpms there is no problem. Imagine my surprise when a suburban starting eating my bumper when I thought I was going to be able to get on up out of his way. Has anyone had any problems like this? or know whats going on with my truck?

2003 Duramax/Allison stock with Superchips programmer, 51000 miles, crew cab swb 4x4

Also, i started getting blue smoke at one point when it started defueling

Have you tried reading the codes w/ your superchips?

Bob the Builder

If your getting RPM hindered you should look else where than the Allison,like say the fuel filter for starters.

yes, no trouble codes, and there is a new fuel filter in place.

Bod the builder when you say defueling what exactly do you mean because I think I have a similar problem that you are describing. At about 2500-2700 rpms the smoooooth sound of the diesel makes like a knocking noise....almost like the sound of valves knocks on a gasoline engine. Or is this sound something that a diesel makes at high rpms? Sorry just trying to learn a few things!

racer, in those high of rpms you shouldn't hear any engine noise besides you turbo spooling. When these engines defuel it isn't a noise that you hear it is the productivity of the engine that changes. In my case, the fuel filter was to blame cause my fuel pressure to be to low for engine operations in the upper rpm band. Don't worry and don't apologize for asking questions. The only way to learn anything is to be told/read the information. Most of the time that means asking questions. I am by far no expert on diesel engines but I do know a few things. The sounds you describe sound like the sound the engine would make if the turbo wasn't engaged. Is the sound equivalent to the sound the engine make at idle? during the low rpm bands? Have you thrown any trouble codes/check engine light?

Bod the builder when you say defueling what exactly do you mean because I think I have a similar problem that you are describing. At about 2500-2700 rpms the smoooooth sound of the diesel makes like a knocking noise....almost like the sound of valves knocks on a gasoline engine. Or is this sound something that a diesel makes at high rpms? Sorry just trying to learn a few things!

THE PILOT INJECTION TURNS OFF AT AROUND 2500-2600 RPMS.........My 2002 will get louder above that rpm as well............it's normal.

T:cool: NY.
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Bob no codes, I think I got it though the filter needed changed. Put a new one on and problem has stopped hope this helps you. I wish I could describe it better but I was having a similar problems as you.