96bulldogpower Posted January 24, 2018 Share Posted January 24, 2018 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! Help guys! Thanks in advance! Quote Link to comment https://www.bigmacktrucks.com/topic/52299-ac-427-intermittent-low-power/ Share on other sites More sharing options...
Mackpro Posted January 24, 2018 Share Posted January 24, 2018 You got the dreaded 4-5 code which can be a pain to fix. 37 psi is up there . Usually 33-35 max. A turbo calibration on the laptop might show what's wrong. Quote Link to comment https://www.bigmacktrucks.com/topic/52299-ac-427-intermittent-low-power/#findComment-390436 Share on other sites More sharing options...
fjh Posted January 25, 2018 Share Posted January 25, 2018 Try changing the VGT Filter! Quote Link to comment https://www.bigmacktrucks.com/topic/52299-ac-427-intermittent-low-power/#findComment-390497 Share on other sites More sharing options...
Jamkar Posted January 25, 2018 Share Posted January 25, 2018 I get the same issue with my CCRS when the waste gate actuator fails. Quote Link to comment https://www.bigmacktrucks.com/topic/52299-ac-427-intermittent-low-power/#findComment-390512 Share on other sites More sharing options...
Fritz Posted July 10, 2023 Share Posted July 10, 2023 On 1/24/2018 at 10:29 AM, 96bulldogpower said: 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! Help guys! Thanks in advance! What was the problem? I have the same issues. Quote Link to comment https://www.bigmacktrucks.com/topic/52299-ac-427-intermittent-low-power/#findComment-534560 Share on other sites More sharing options...
Joey Mack Posted July 10, 2023 Share Posted July 10, 2023 Hey there. Your posting on a 5-1/2 year old thread.. I suggest you start a thread, and give Mack,model, year,engine series, and tranny model, I you can... A lot of guys will see the new thread faster.. welcome aboard... Jojo Quote Link to comment https://www.bigmacktrucks.com/topic/52299-ac-427-intermittent-low-power/#findComment-534570 Share on other sites More sharing options...
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