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Sudden engine power loss

My boyfriend's 2004 GMC Sierra 2500HD 6.0 litre gas engine truck has been idling really high and when were driving down the road it doesn't seem to have any power, then suddenly the power kicks in and the truck runs kinda normal, we have a bully dog system in the truck and it doesn't say anything is wrong with the truck, and sometimes when we are driving it will quit but will restart immediately, the truck also has a 6 inch suspension lift in it also, can someone help? We have been thinking about maybe replacing the computer but want to know other things to check before we have to spend a fortune on a computer.

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  • GMC Master
  • 21,873 Answers

Are you saying the check engine light is not on, and there are no trouble codes stored ?

Posted on Jul 10, 2013

  • 1 more comment 
  • Toni Edwards Jul 10, 2013

    When the check engine light comes on he uses the bully dog system to see what wrongs and it didn't have any codes, and sometimes he does check without the engine light being on to see if there are any codes and there aren't any

  • Toni Edwards Jul 10, 2013

    there are codes sometimes when the light is on, and when it is always has MAF Sensor code and already replaced MAF Sensor with new part, and sometimes when lights on also 2 System to lean codes and when he clears codes nothing changes, and once in awhile it wont shift into overdrive and he scans it with bullydog scanner and it brings only the MAF Sensor code and when he clears code it instantly shifts into overdrive and also roughly 8 months ago it burned out a new altenator that was less than a year old then replaced with used one from other truck and it worked. For long time now its only running between 12-13 volts charge

  •  Stephen
    Stephen Jul 11, 2013

    I should tell you replacing a component only fixes a problem about 50% of the time. A code is only a guide for the mechanic for what to check. The MAF code could be caused by a wiring problem or something in the fresh air intake. The sensor may be reading correctly but the computer does not like the data. Same thing with the O2 sensors. If another sensor makes the computer lean out the injectors, the O2 sensors will read the mixture is too lean, which it may well be. You usually need the shop manual to get the testing procedures for each code.



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