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2011 Mack Gu713 mp7 low power issue


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Let me say first I am not coming with a lot of information, I know this, but I'm just kinda hoping someone has seen this problem before and can lead me in a direction to begin. I haven't got the truck to a shop yet, mainly because I can't find a shop local to me that knows Mack's well enough for me to trust, and I can't afford the downtime at the wrong shop. Hopefully I can explain the problem clear enough to understand.

Alright, a few days ago I'm hauling rock out of the quarry, first load goes fine. Second load I stop at a friends shop to chat. Go to leave and the problem presents itself. It happens in every gear, it does not clear up at any certain rpm but happens in the range of off idle up to around 1500 rpm. In that range the truck acts like it has 0 power, but when it reaches around 1500 rpm, it's like a switch is turned on and the power is there to the top of the rpm's. Truck idles fine, only code set is the turbo speed MID 128 PID 103 FMI 9. This code has been on for a while before this problem developed, and even after changing the sensor, I believe the code is a wiring problem I haven't been able to track down. Other than this problem the truck runs good, great oil pressure, fires right up, idles fine. I just bought the truck at 415,000 from a dealer and have no information on previous work or records.

I'm getting the truck to a friends shop this weekend, he is a good mechanic but not much experience on a Mack especially the mp7 or mp7. Going to get the computer on it and see if anything shows. Again I'm just posting here in hopes someone has seen a similar problem and can give pointers. Winter and breakdowns have been rough, work is firing back up and I can't afford to miss any more time than needed, and dang sure can't afford to let someone work on it that's just going to throw parts at it till it's fixed, so maybe I'll get lucky with experienced advice. I hope to have it at my buddies shop and on the computer tomorrow afternoon or Sunday so I'll report back with any info from the computer diagnostics.

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does your friend have Premium Tech Tool, or a professional equivalent?  Please go in with caution...  'changing parts' isn't just 'changing parts' on these Volvo's..  you can easily cause more issues..  So please study up on this... if your friend had VED12 knowledge, then He may be close enough...   jojo

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After looking at that code, it CAN cause a derate. Look for a broken wire/short to ground on the sensor circuit. 

Edited by Onyx610
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Posted (edited)

Per Mack the code does not lead to a turbo problem, it shows as a problem with either the sensor or wiring harness. The code has been on for over a month with no adverse effects on the truck so why now would it start causing a problem? The actuator was recalibrated and passed testing just a few weeks ago. The code does not come on or go off, it stays constant so why would it cause (or anything for that matter) a derate only at certain rpm's and not at others?

Please don't take this as being argumentative, I am genuinely just trying to understand the reason you would think as you are, I'm seriously trying to absorb the information as future reference and a learning situation. I'm not at all ignorant to mechanics or trucks but I am admittingly severely under educated on the Mack/ Volvo engines (guess I should swap the order of those two but I would rather give Mack precedence over Volvo lol).

Edited by Toyota231
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4 hours ago, Joey Mack said:

does your friend have Premium Tech Tool, or a professional equivalent?  Please go in with caution...  'changing parts' isn't just 'changing parts' on these Volvo's..  you can easily cause more issues..  So please study up on this... if your friend had VED12 knowledge, then He may be close enough...   jojo

Honestly I can't remember what software he has but I will check tomorrow, I know it is a professional grade equipment, he isn't some jack leg idiot, he is a very good mechanic that has been workeing in dealerships for years before going on his own, sadly Mack/Volvo is the least of his experience. But the one exact reason I am taking it to him is he will NOT just throw parts at it, he will diagnose, and the fact that i can go there and work to help take some burden off an up front bill right now helps me out greatly right now.

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Yea well without PTT I can’t tell you much more then that. These trucks are a nightmare to diagnose even in person. So it’s nearly next to impossible to do it over the internet for most issues. Volvo/Mack says for that code it can cause a derate, and to check for short to ground/broken wire in the turbo speed signal wire. 

Edited by Onyx610
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Believe it or not sometimes the only way to fix these trucks is to throw parts at them….it’s sad I know, but it’s really what it’s come to.

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10 minutes ago, Onyx610 said:

Yea well without PTT I can’t tell you much more then that. These trucks are a nightmare to diagnose even in person. So it’s nearly next to impossible to do it over the internet for most issues. Volvo/Mack says for that code it can cause a derate, and to check for short to ground/broken wire in the turbo speed signal wire. 

I understand how hard it is to diagnose over the internet, I'm not asking for a diagnosis, I'm asking for experience. What I mean by that is kind of an old school mechanic like me, someone that has been through a lot of diagnosis situations and remembers, "hey, I seen something similar to that one time, and this is what it was". But mostly in this situation I'm more curious on an explanation so I can understand the thought process. What I mean is, in my mind I can't wrap my mind around why the code could have been on for so long, will come back immediately after being cleared, why would it now be causing this problem, and even more so why would it cause a derate so constantly at only certain rpm's? Again not at all being argumentative, if there is reasoning behind it or if it's been seen before I will thoroughly listen, I know my questioning and reasoning is such a pain in the ass, I just genuinely want to use it as a learning situation where I can absord the info for my knowledge and learning and hopefully something I can pass on one day.

I can't express how much I know to fix the code first, and should have already been fixed, but thanks to a severe neck and back injury I'm terribly limited on when and how I can do anything. Then on top of everything thanks to these awesome times we live in, in my area it is so hard to find a decent shop that isn't backed up for weeks, and most importantly has knowledgeable people. I don't mind paying twice what it costs to get a knowledgeable shop and person to diagnose and fix, but ill be damned if I pay a dime for someone to throw thousands in parts at a shot in the dark, that's exactly why I am so leary of local shops these days, I've found most are full of nothing but parts changers that couldn't do diagnostic work if their lives depended on it, then being a reasonably knowledgeable person with decades of experience on small diesel, automotive, and fabrication it just makes it worse, especially when I'm no longer able to do all the things I used to.

Again I'm sorry my questions are such a pain, and i am such a pain, I just have one of those brains that never stops, that over analyzes everything.

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Don’t be sorry for the questions, that’s why a lot of us are here. We enjoy helping others fix their problems or just teaching. We also learn a lot through people like you. If they actually come back and tell us the fix….haha. I completely understand where your coming from on everything you touched on and I agree 100% The problem with these trucks is it’s pretty rare you get the “hey I seen that before” these trucks have a mind of their own. You could get codes for one thing and have it be something completely different. You can see something a few times and then it’s different another time. Sometimes the only way to fix these is to change parts until the light goes out, as stupid as that sounds…I called in air support for the big dogs, stand bye…help will be here. 
 

 

 

 

 

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Toyota,   you are fine..  there is a boatload of knowledge here.. I'm glad that the mechanic you know is a good one..  Here in central N.C. the issue's are the same. I left the dealership 13+ years ago and went out on my own as well. I did try to go back to the dealership, I lasted 2 years, and couldnt handle the inside politics, and seeing customers get hit hard in the pocket.  Keep in touch with us..  Jojo

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