springerj10 Posted December 31, 2021 Share Posted December 31, 2021 I’ve got a 2011 Mack with an MP7 in the shop with a rough idle, jumping between 600 and 650 RPM and low power. Truck has no fault codes. It’s gotten a new EGR pressure sensor, EGR valve, Fuel pressure relief valve, fuel filters. EGR cooler was clean when checked. Removed and checked for debris in fuel lines going to ECM cooling plate. Fuel pressure jumps around between 50 and 60 PSI at idle. No air bubbles in return line going back to tank. Any ideas? Quote Link to comment https://www.bigmacktrucks.com/topic/68997-2011-mp7-low-power/ Share on other sites More sharing options...
Onyx610 Posted December 31, 2021 Share Posted December 31, 2021 Not too much info to go off of yet, but I believe 50-55 psi is the idle fuel pressure. Have you checked pressure under load? Maybe a fuel pressure regulator? Quote Link to comment https://www.bigmacktrucks.com/topic/68997-2011-mp7-low-power/#findComment-486234 Share on other sites More sharing options...
springerj10 Posted December 31, 2021 Author Share Posted December 31, 2021 Haven’t checked it under load but at wide open throttle it jumps up to about 90 PSI. During a test drive it will have an intermittent skip bad enough to make the truck surge. Quote Link to comment https://www.bigmacktrucks.com/topic/68997-2011-mp7-low-power/#findComment-486236 Share on other sites More sharing options...
springerj10 Posted December 31, 2021 Author Share Posted December 31, 2021 I swapped the valve on the front left side of the head with one out of a running truck, didn’t make a difference. Quote Link to comment https://www.bigmacktrucks.com/topic/68997-2011-mp7-low-power/#findComment-486237 Share on other sites More sharing options...
Onyx610 Posted December 31, 2021 Share Posted December 31, 2021 Sounds like good fuel pressure to me. I’m assuming you have Premium tech tool? Quote Link to comment https://www.bigmacktrucks.com/topic/68997-2011-mp7-low-power/#findComment-486241 Share on other sites More sharing options...
Joey Mack Posted December 31, 2021 Share Posted December 31, 2021 are you having issues with the power steering as well? jojo Quote Link to comment https://www.bigmacktrucks.com/topic/68997-2011-mp7-low-power/#findComment-486242 Share on other sites More sharing options...
Onyx610 Posted December 31, 2021 Share Posted December 31, 2021 5 minutes ago, Joey Mack said: are you having issues with the power steering as well? jojo Good call Joey, how many miles are on the truck, what kind of truck is it, and anything previously done to it before this started? Quote Link to comment https://www.bigmacktrucks.com/topic/68997-2011-mp7-low-power/#findComment-486243 Share on other sites More sharing options...
Joey Mack Posted December 31, 2021 Share Posted December 31, 2021 I dont want to jump too far ahead, but I have fixed this issue a few times... you reckon this has caused an issue, and the drive ends are worn out between the tandem pumps? jojo Quote Link to comment https://www.bigmacktrucks.com/topic/68997-2011-mp7-low-power/#findComment-486244 Share on other sites More sharing options...
springerj10 Posted December 31, 2021 Author Share Posted December 31, 2021 It’s actually a 2012 not 2011. GU713 roll off truck, 296000 miles on it. Power steering works fine. I’m using Tech tool. I’ll pull the gear out and check it. The truck originally came in requesting a regen with no fault codes. That’s when I put the EGR valve on because it wouldn’t get up to temperature. It regened after that. Quote Link to comment https://www.bigmacktrucks.com/topic/68997-2011-mp7-low-power/#findComment-486264 Share on other sites More sharing options...
springerj10 Posted March 3, 2022 Author Share Posted March 3, 2022 Ended up sending the truck to Mack, didn’t have the time to diagnose and repair it while maintaining all of our other trucks. It had 3 out of round cylinders. Mack did a full rebuild on it. Quote Link to comment https://www.bigmacktrucks.com/topic/68997-2011-mp7-low-power/#findComment-490797 Share on other sites More sharing options...
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