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Discussion Starter #1
I’ve got this Denali 5.3L that has 105k miles and it seems like it’s down on power. Mileage also seems worse than normal too but I’ve only had it for 5k miles.

There are no codes, no lights on the dash to indicate a problem but it sure seems like there is a problem.

Any clues on what to look at?

thanks
 

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2004 chevy trailblazer_lt
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Have you connected a code reader/scanner to see if there are any codes?
 

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When you turn your ignition key to the on position, do you see a check engine light?
 

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Good.

OK, first thing I would do is to find out what the fuel pressure is. If you do not have a fuel injector pressure gauge, you can get a loaner one from O'Reilly or Autozone auto parts. Since there is no external fuel filter, I won't suggest you change it.

How long have you owned this Envoy?
 

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Discussion Starter #8
Bought it from a friend at work that was retiring for $1000 with 100K. It has about 108K now. I was thinking fuel pressure too but I’m surprised there’s no check engine light if that’s the cause.
 

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Check engine light will not come on for low fuel pressure. Also, do you know when or if the spark plugs were ever changed, and if they were, what spark plugs were used?
 

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Discussion Starter #10
I know he had a tune up done at the dealership. My guess is the fuel pump is getting weak. Do you know what the pressure is supposed be?
 

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See if you can find out at what mileage the tune up was performed. Also, check your air filter.

I believe the key on, engine off fuel pressure should be in the range of 55 - 62 psi. If it is lower than 55, the pump is dying. Also, only replacement pumps to consider are ACDelco or Delphi. Most any other brand will likely be a piece of junk.
 
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