Hey guys! I have a question for those familiar with the Mack AC engines.. I have a 2004 Mack vision with the AC 427 and I’m having trouble with the engine going into de-rate as soon as it enters boost. This happens at any speed while the engine is at higher rpm and producing boost, engine already feels sluggish but when it de-rates it falls flat on its face. The lighting bolt comes on the dash when it de-rates however you can take your foot off the accelerator and let the boost come down and it makes the lighting bolt light turn off and de-rate cancels, until you get back on the pedal and builds back boost, then the cycle repeats itself. This truck has the co-pilot display and it shows me (MID 128, SID 269, FMI 7). When loaded the truck can barely sustain its own speed and on hills where it builds boost I can lose speed down to 35mph. I’m getting good boost up to about 37 psi. The turbo relief valve is good and the turbo vane actuator is cycling and doing its job. Egr valve seems to cycle and perform correctly as well. No smoke of any kind out of the exhaust pipe ever, even if you lug the engine.. you just never get smoke out of it.
I just got off the phone with Mack but their shop is way too behind to even consider taking my truck off the road!
AC 427 intermittent low power
in Engine and Transmission
Posted
What was the problem? I have the same issues.