makuzara Posted December 5, 2017 Share Posted December 5, 2017 I work for the state DOT, we have a 2014 Mack Granite GU713 that is set up as a snowplow. It has an Allison automatic. About a year ago, it started losing power in all gears and surging in 4th gear. This only happened when pulling a hill or pushing heavy snow. Our mechanics were unable to find anything wrong. It continued getting worse until it now surges between 1000 and 1200 RPM in 4th gear, so hard it lifts the plow off the ground, about a 50% loss of power in other gears (under load or climbing a hill) from what it had before. If you let off the throttle and let it get down to 1000 RPM or below it starts backfiring through the exhaust (only in 4th gear, other gears lug down to 800-900 RPM just fine). It upshifts at 1250 RPM instead of 1400-1600 like the rest of the gears. It went to the Mack dealer, and they ran the rail, camshaft was bad and some valves were too. All were replaced, problem did not go away. If it is run on flat ground unloaded, it works fine, as soon as you start an incline or start pushing snow, it falls on it's face power wise. It will surge and backfire on level ground in 4th if you are pushing heavy snow. Our mechanics have run diagnostic on it, only thing they find is error codes for some sensors, mainly oil pressure. It has also gone through 4 fuel level sending units, as the shaft breaks. They had left some of the pieces in the tank, but we convinced them on the last one to pull them out. No change. Now it is starting to surge in 3rd gear between 1400-1600 RPM, not as bad as in 4th, but starting out like 4th gear did. Transmission diagnostic shows nothing, no error codes. Our mechanics replaced transmission fluid and filter, no change. This thing is driving me nuts, any help would be appreciated. Quote Link to comment https://www.bigmacktrucks.com/topic/51862-2014-granite-low-power-surging-in-4th-gear-backfiring/ Share on other sites More sharing options...
Dirtymilkman Posted December 5, 2017 Share Posted December 5, 2017 Were injectors done on this truck? Quote Link to comment https://www.bigmacktrucks.com/topic/51862-2014-granite-low-power-surging-in-4th-gear-backfiring/#findComment-386604 Share on other sites More sharing options...
fjh Posted December 5, 2017 Share Posted December 5, 2017 What codes is it throwing up? kind of a vague post if you want help! Sounds as if its starving for fuel Quote Link to comment https://www.bigmacktrucks.com/topic/51862-2014-granite-low-power-surging-in-4th-gear-backfiring/#findComment-386641 Share on other sites More sharing options...
makuzara Posted December 6, 2017 Author Share Posted December 6, 2017 Codes were for bad oil pressure sensor, bad coolant temp sensor, both were replaced. Coolant temp sensor was bad because of serpentine belt failure, broken end whipped around and broke it. I don't know if injectors were replaced. The mechanics did not remove the broken parts of the fuel sending unit form the fuel tank the first 3 times. Removed all they could find the 4th time. Quote Link to comment https://www.bigmacktrucks.com/topic/51862-2014-granite-low-power-surging-in-4th-gear-backfiring/#findComment-386725 Share on other sites More sharing options...
Phase 1 Posted December 6, 2017 Share Posted December 6, 2017 On 12/5/2017 at 8:06 AM, fjh said: What codes is it throwing up? kind of a vague post if you want help! Sounds as if its starving for fuel Agree Quote Link to comment https://www.bigmacktrucks.com/topic/51862-2014-granite-low-power-surging-in-4th-gear-backfiring/#findComment-386726 Share on other sites More sharing options...
fjh Posted December 7, 2017 Share Posted December 7, 2017 We had a similar occurrence a month or two back it was the injector wiring harness it gives the same sounds and feel as running out of fuel! this could be a possibility ! Quote Link to comment https://www.bigmacktrucks.com/topic/51862-2014-granite-low-power-surging-in-4th-gear-backfiring/#findComment-386793 Share on other sites More sharing options...
makuzara Posted December 7, 2017 Author Share Posted December 7, 2017 Problem found!! something to keep in mind if anyone has a similar problem. The baffle in the fuel tank had inadequate or substandard welds and completely broke free, floating and moving around in the tank. That is what was taking out the fuel sending units as well as intermittently causing the fuel gauge to not read correctly. One of the pieces from one of the broken fuel sending units was partially blocking the outlet, as well as the baffle was occasionally wedging itself against the outlet. New fuel tank on the way. So if anyone has problems after a sending unit goes bad or the fuel gauge starts reading (or not reading) incorrectly, check to see if the baffle is broken loose. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/51862-2014-granite-low-power-surging-in-4th-gear-backfiring/#findComment-386832 Share on other sites More sharing options...
41chevy Posted December 8, 2017 Share Posted December 8, 2017 Thanks for posting your fix. Paul 1 Quote "OPERTUNITY IS MISSED BY MOST PEOPLE BECAUSE IT IS DRESSED IN OVERALLS AND LOOKS LIKE WORK" Thomas Edison “Life’s journey is not to arrive at the grave safely, in a well preserved body, but rather to skid in sideways, totally worn out, shouting ‘Holy shit, what a ride!’” P.T.CHESHIRE Link to comment https://www.bigmacktrucks.com/topic/51862-2014-granite-low-power-surging-in-4th-gear-backfiring/#findComment-386877 Share on other sites More sharing options...
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