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5.3 Lags When Cold

Z71GMC

By Z71GMC
in Ask A GM Technician

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Z71GMC Enthusiast

Z71GMC

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I have a GMC 1500 5.3 and when the engine is cold it has almost no power and some times back fires for about the first minute when driving then it stops. It is all stock except for a K&N filter. I also seem to get very poor mileage about 13-14 on the highway. What could be the problem? Thanks.

Z71GMC Enthusiast

Z71GMC

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how many miles are on the truck??, and what year is it??

 

It is a 99 and has about 100,000 miles on it, I just serviced it with new fuel filter, cleaned K&N, I also ran some fuel system cleaner through it about 6 tanks ago. It has been doing this for about 1 year.

C6Racer Enthusiast

C6Racer

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Have you changed the spark plugs and wires? I changed mine at 90k miles. I still have the stock O2 sensors(I'll probably change them soon though) and I can get 22 mpg on the highway. Average is about 14 mpg. See below for all the info on my truck.

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