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Poor fuel economy on a 2008 Chevrolet 2500 HD ltz, 4x4 Duramax

The best fuel so far is 9.7 mpg. The truck runs great, but when you let off the accelerator, it feels like something is slowing the truck down and you can watch the speedometer drop. The transmission is shifting fine and it is not locked into 4wd and its not in tow/haul mode. The computer shows 198 miles to empty when I fill it up 26 gallon tank. An exact truck like mine gets 14.5 or better and around 300 to a tank on the same identical truck, and it doesnt feel like its being dragged down. Any Ideas?

Posted by Anonymous on

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  • Cars & Trucks Master
  • 786 Answers

Sounds like an overrun sprag problem or torque converter problem. Perform an OBDII scan for any transmission faults. The ECU controls some trans functions. In your comparison, did both trucks have same transmission( Allison, Hydramatic) ? Did they both have same rear axel ratio?

Posted on May 22, 2017

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Posted on Jan 02, 2017

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SOURCE: Chevrolet 2500 Not Running, May Be Fuel Filter Sensor

That red wire is only for the fuel heater.will not cause a no start.try pumping the primer pump on top of the fuel flter hsg. but first open the bleed screw,which is black plastic also located on the top.this will eliminate any trapped air that might have entered the fuel intake system.if the pump does not get firmer and harder to push, then you have a leak in the fuel supply lines or the ck valves in the fuel filter hsg or stuck open. Still no start have it scanned to ck fuel pressure while cranking.it should be close to 5000 lbs

Posted on May 14, 2008

SOURCE: 02 gmc allison tran. wont go into tow-haul mode

THERE HAVE BEEN ALOT OF PLOBLEMS WITH THE SHIFTER HANDLE/SWITCH. THE BEST WAY TO VERIFY CONCERN IS USE A DIAG. SCANNER & VIEW TRANSMISSION DATA DISPLAY WHILE ENGINE RUNNING. THE SWITCH IN THE SHIFTER IS FAULTY. IF YOU SEE NO INPUT CHANGE WHILE DEPRESSING SWITCH THIS IS YOUR CONCERN.

Posted on Nov 08, 2008

  • 99 Answers

SOURCE: Chevrolet 2500 Not Running, May Be Fuel Filter Sensor

if it dont have good compression it will not start check the comp and make sure there no water in oil if fuel pressure is low it will not pop the injector open try some starting fluid

Posted on Jan 26, 2009

  • 192 Answers

SOURCE: 2007 chevy silverado 2500 hd duramax shut down

mo me it sounds like low fuel volume i would check my lift pump

Posted on Sep 30, 2009

  • 1608 Answers

SOURCE: 2007 Silverado, 6.6 Duramax w/Allison

There is a service bulletin for this condition.It has to do with a ceramic high pressure valve ball fracture inside the fuel injection pump,which may lead to internal pump damage resulting in low fuel rail pressure.This could contaminate the fuel rails and injectors with debris.The fuel pump will operate but with reduced output flow.The fuel injection pump will have to be replaced or repaired.Look and see if there are any repair shops that specialize in injection pumps.Hope this helps.Good luck.

Posted on Apr 06, 2010

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