ghmallard Posted April 7 Share Posted April 7 Have 07 Ai 427 that the boost drops off when pulling hard loaded. Boost will be 30+ and fall back to 20-22 then will come back and fall out again. No change in rpm’s just boost psi. Boost Does not drop out when empty even when accelerating hard. No lights or codes coming on when boost drops. Truck has 148,000 original miles 13 speed and 4.17 rears. Any help be appreciated on what might be going on? Quote Link to comment https://www.bigmacktrucks.com/topic/75379-07-mack-granite-ai-427-boost-drop/ Share on other sites More sharing options...
Joey Mack Posted April 7 Share Posted April 7 Do you hear the sound of air rushing through a leak ? Im curios about a boost leak that opens when pressure is up. What type of turbo do you have and does it have a waste gate? Quote Link to comment https://www.bigmacktrucks.com/topic/75379-07-mack-granite-ai-427-boost-drop/#findComment-573067 Share on other sites More sharing options...
ghmallard Posted April 7 Author Share Posted April 7 We dont hear air rushing thru leak when boost pressures up. It will stay 30 plus boost when empty and never fall. Only falls when pulling hard loaded Quote Link to comment https://www.bigmacktrucks.com/topic/75379-07-mack-granite-ai-427-boost-drop/#findComment-573069 Share on other sites More sharing options...
Joey Mack Posted April 7 Share Posted April 7 With no change in RPM's, does that mean you dont have power loss? Just see it on the gauge? Quote Link to comment https://www.bigmacktrucks.com/topic/75379-07-mack-granite-ai-427-boost-drop/#findComment-573070 Share on other sites More sharing options...
ghmallard Posted April 7 Author Share Posted April 7 Correct see it on gauge and can feel and hear boost fall off and come back Quote Link to comment https://www.bigmacktrucks.com/topic/75379-07-mack-granite-ai-427-boost-drop/#findComment-573071 Share on other sites More sharing options...
Joey Mack Posted April 7 Share Posted April 7 Im at a loss, guess im not awake yet. 😉 Quote Link to comment https://www.bigmacktrucks.com/topic/75379-07-mack-granite-ai-427-boost-drop/#findComment-573072 Share on other sites More sharing options...
ghmallard Posted April 7 Author Share Posted April 7 We checked it for boost leaks had none, when boost falls out its a dog. Typically just keep accelerator pushed it comes back for few minutes then falls out again. Just does it when pulling loaded not when empty. Quote Link to comment https://www.bigmacktrucks.com/topic/75379-07-mack-granite-ai-427-boost-drop/#findComment-573074 Share on other sites More sharing options...
Joey Mack Posted April 7 Share Posted April 7 Is the speedometer acting up ? Quote Link to comment https://www.bigmacktrucks.com/topic/75379-07-mack-granite-ai-427-boost-drop/#findComment-573076 Share on other sites More sharing options...
ghmallard Posted April 7 Author Share Posted April 7 No went ahead anyways and pulled sensors bell housing , back if tranny and front of motor to check em to rule that out 2 Quote Link to comment https://www.bigmacktrucks.com/topic/75379-07-mack-granite-ai-427-boost-drop/#findComment-573077 Share on other sites More sharing options...
fjh Posted April 7 Share Posted April 7 Here is a bit of an off the wall thing to try ! Bypass your air drier temporarily and see if the issue goes away! I have seen air driers dump boost before! Just sayin! Quote Link to comment https://www.bigmacktrucks.com/topic/75379-07-mack-granite-ai-427-boost-drop/#findComment-573092 Share on other sites More sharing options...
Mackpro Posted April 9 Share Posted April 9 Had a very similar problem with a 2005 CV713 AI engine. Boost would build up great for a few seconds and then drop back to what felt like 3/4 throttle. Replaced injectors, adjusted valves , replace muffler, pressure tested intake system, check fan clutch for staying on, check parameters such as tire size and gear ratio in ECM. Engine ECM was at step 10 and VECU was at Step 12B. All looked perfect. Come to find out there are different versions of the Step 12B program and there was a Step 10A update on the engine ECM that was not visible from the dealership side. Tech support set up a different version of the Step 12 B and an updated engine ECM software. Installed the updates and ran %100 better and held boost at the 30 psi under a load all the time. Hopefully you can find a dealership that will do the updates 1 Quote Link to comment https://www.bigmacktrucks.com/topic/75379-07-mack-granite-ai-427-boost-drop/#findComment-573286 Share on other sites More sharing options...
ghmallard Posted Wednesday at 01:05 AM Author Share Posted Wednesday at 01:05 AM On 4/9/2025 at 9:22 AM, Mackpro said: Had a very similar problem with a 2005 CV713 AI engine. Boost would build up great for a few seconds and then drop back to what felt like 3/4 throttle. Replaced injectors, adjusted valves , replace muffler, pressure tested intake system, check fan clutch for staying on, check parameters such as tire size and gear ratio in ECM. Engine ECM was at step 10 and VECU was at Step 12B. All looked perfect. Come to find out there are different versions of the Step 12B program and there was a Step 10A update on the engine ECM that was not visible from the dealership side. Tech support set up a different version of the Step 12 B and an updated engine ECM software. Installed the updates and ran %100 better and held boost at the 30 psi under a load all the time. Hopefully you can find a dealership that will do the updates Hope so truck has been at mack dealer for 7 days. Not finding anything yet. No code on mack computer, good fuel psi, no boost leak. All parameters are set goof. Boost only drops out in last 2 gears on high side. Mack computer shows nothing else dropping out but boost. Will drop out for 20/30 seconds then come back. Hopefully they get it figured out. Im scratching my head. Quote Link to comment https://www.bigmacktrucks.com/topic/75379-07-mack-granite-ai-427-boost-drop/#findComment-573773 Share on other sites More sharing options...
Mackpro Posted yesterday at 05:06 AM Share Posted yesterday at 05:06 AM 4.17 gears with a AI engine is awful high gears unless your running short 22.5 lo-pro tires. The AI engine dump truck guys here run 4.42 gears with full size 22,5 tires or 24.5 low-pro or full size 24.5 tires. The favorite seems to be 4.74 rear gears with 24.5 full size tires. This keeps the RPM’s in the narrow torque/HP band of the AI engine. Quote Link to comment https://www.bigmacktrucks.com/topic/75379-07-mack-granite-ai-427-boost-drop/#findComment-573841 Share on other sites More sharing options...
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