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  1. #1
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    Default Understanding Fuel Injection & MPG Loss

    Hey All,
    I am working on diagnosing a pretty substantial drop in MPG on my 2006 Silverado 1500 4x4 w/ the 5.3L. For 70,000 miles I never reset my AVG MPG calculator and I was running at 16.8 combined city and highway. At about 70,000 I noticed the AVG MPG start dropping so I reset it and over the past 10,000 miles I have been averaging 15.3 MPG.

    Here is what has changed since about 60,000:
    - Switched to synthetic blend oil
    - Increased tire pressure to 39 psi up front and 38 psi in the rear (should help some)
    - Ran some seafoam through the intake (thought it might help clean things up a bit)

    Oil is changed on average every 4k miles, I run 87 octane, regularly change air filter. Based on the research I have done here the only things I can think of that could be causing this are the fuel injectors (dirty), throttle body (dirty), or the computer.

    I dont know enough about how this engines fuel injection system works to get any further so I was hoping someone could chime in with some ideas but I would really like to understand how this engines FI system works.

    Thanks!

  2. #2
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    TRPLXL2's Avatar
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    Default

    You said you did a seafoam treatment, but you didn't say anything about doing a tune up or changing the plug or anything of that nature. If I'm not mistaken that's what they want you to do after using that stuff, but I am not 100% sure either.

    Another thing is the fuel injectors, if you have never used injector cleaner on your truck and it already has 70,000 miles I would definately not start now. You could cause more damage to them doing that, all of the junk will float right up into the manifold and clog the injectors.

    Hopefully someone else will pitch in with better info,...........:out:
    2004 Chevy Colorado
    LS1 5.7 swap/TBSS rear axle swap

  3. #3

    Default

    I would look into new AC delco plugs and a good set of wires
    David
    2004 Silverado 2500 Crew Cab 4x4, AMSOIL EA air filter, Granatelli MAF sensor, Throttle body spacer, Magnaflow exhaust (true dual to 2 in 1 out muffler), 6" ProComp lift (add a leaf and 5" superlift rear block), Bilstein shocks, 35's (Cooper Disoverer ST) and 4.10 gears, Rhino Liner, EGRUSA fender Flares and widow visors, extended stainless steel brake lines, firestone airbags w/onboard air compressor, Pioneer Avic X940BT navigation, Accel backup camera.
    http://www.gmtruckclub.com/forum/sho...Silverado-2500
    1960 Land Rover Series II 88
    2001 Pontiac Sunfire
    2013 Toyota Avalon Limited (Wife's Car)
    NRA Life Member

  4. #4
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    Default

    Sorry Guys - I completely forgot the plugs and wires. At about 65-70k I replaced the plugs with Delco Iridiums (same as stock) and replaced the wires with 8mm MSD wires. As far as fuel injector cleaner, I run it through periodically. Not on any set schedule, but I would say on average every 15k miles or so.

    Does fuel injector cleaner clean the throttle body as well?

  5. #5
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    TRPLXL2's Avatar
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    No fuel injector cleaner just cleans the fuel rail, and the accompanying lines and such. GM sells a throttle body cleaner, it is designed to not scratch the plate as some of the generic cleaners do. I think you can buy it right at the GM dealership, it's only like $10 for a big aerosol can of it.

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