mackr1989 Posted November 24, 2016 Share Posted November 24, 2016 I have a 2007 mack granite with a 400. How do I get more hp out of the engine? Quote Link to comment Share on other sites More sharing options...
Mackpro Posted November 24, 2016 Share Posted November 24, 2016 Lots of threads on here about the AI engine " low power complaints ". We always start with , check fuel pressure, test drive and check boost pressure and leak test intake system. Ajust valves and replace rocker arm hold down bolts. Update all software to newest levels "Step 12b". Calibrate throttle pedal. Make sure tire size and rear gear ratio are correct in ECM settings. Check muffler for broken baffles. Check and see if trans has been changed or tires to tall for rear gear axle ratio. 4.42 or 4.64 work best unless your running 22.5 low pros. Return truck to customer and let run a few days and if still underpowered start looking at HP change or different software from Mack. Sometimes their generous and let slip a "hot " file out. Happened to me a month back. Quote Link to comment Share on other sites More sharing options...
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