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Greg, ASE Certified Technician
Category: Chevy
Satisfied Customers: 387
Experience:  22+ years of experience on GM vehicles. Shop Owner/lead tech. Specializing in GM products.
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I have a 2003 GMC Sierra,reduced engine power

Customer Question

my 2003 gmc 5.3 sierra has shown "reduced engine power", at that point it has very slow acceleration it has 183000 miles on it has been tuned (plugs,filters etc.) within the last 12000 miles after turning engine off for a short time (15-20 minutes) it will drive normally for weeks or on some occasions months
Submitted: 8 years ago.
Category: Chevy
Expert:  Jaxer Smith replied 8 years ago.

Hi, Welcome to Just Answer!

The most common issue with this model is a failing fuel pump that causes the described condition. If you have not replaced yours yet, you might as well get it over with. Also, the fuel pressure will test just fine when the vehicle is operating just fine. But If you test it when it won't accelerate, you may find it to be lower than normal. Again, this is the most common cause for these symptoms.

If a check engine light is on then it is a whole different story.

If you need further assistance let me know.

Customer: replied 8 years ago.
this does correspond to a check engine light (not sure if it's every time or not) fuel pump has been changed as well as filter problem was on both sides of fuel pump change(before and after) check engine comes from time to time diagnosis at GM indicated it was due fuel vapor at filler in any case it may be off or on from time to time not sure if it pops on with "reduced engine power" or not
Expert:  Jaxer Smith replied 8 years ago.
I am going to open this back up in case one of the other experts has heard of this.
Expert:  Greg replied 8 years ago.
This is most likely a problem with the drive by wire throttle system. If the accelerator pedal position does not coincide with the throttle position then the PCM stores a code for this and limits throttle travel with the reduced power message. Simply cleaning the throttle body real good may take care of this problem! If you know that the throttle body has never been cleaned then definitely do this first. Take the air cleaner hose of at the engine and prop the throttle blade open with the handle end of a screw driver and clean the build up around where the blade seats in the body. Get it real shiny clean and also the edges of the blade. Wipe it out good with a rag. If this does not change this I suggest you get a diagnostic test from a reputable shop with a class 2 capable scan tool. But I bet cleaning the TB will take care of it.
Greg, ASE Certified Technician
Category: Chevy
Satisfied Customers: 387
Experience: 22+ years of experience on GM vehicles. Shop Owner/lead tech. Specializing in GM products.
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