Sporadic power

[CToney]

On. My 03 2500 Smarty Touch 50 hp injectors, FASS, HE351, I have been having a problem with the truck having good power one time I drive it but not the next. Under good conditions I will see 38 psi and 64% load. 24,000 psi rail pressure. Under low power I have a hard time getting to 30 psi but if I rev it high enough I can get 35psi. It maxes out at 47% load. Boost pressure on touch matches analog gauge. With it having power one day but not the next I'm kind of frustrated in tracking done the problem. Usually it's air or fuel. If you are lacking one or the other your hp is limited. I'm not sure where to look.

 

[CToney]

I think I figured out the problem. When my speedometer doesn't work engine is derated.

 

[cerberusiam]

That would be unusual, not impossible but highly unusual. With a 6 speed there really is no engine management tied to speed other than the 110 mph speed limit. It is entirely possible it is reading the signal as to fast when it really isn't. The 03's had issues with the A & B connectors on the ECU corroding and all manner of glitches showing up. The speedo signal is fed to the ECU from the ABS then routed to the cluster on the data bus, possibly something in the circuit is bad including the sensor on the rear diff.