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Drop in 8.1 big block fuel economy--any ideas?

This is a discussion on Drop in 8.1 big block fuel economy--any ideas? within the GM Trucks forums, part of the Vehicle Specific category; I have a 2004 Suburban with the big block 8.1. Has 106K on the clock. I generally do all highway ...

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    Member erikzola's Avatar
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    Drop in 8.1 big block fuel economy--any ideas?

    I have a 2004 Suburban with the big block 8.1. Has 106K on the clock. I generally do all highway miles and sometimes drive within the real speed limit. I have seen a several mpg drop in economy lately that I can't explain. (I know that an 8,000 lb truck with this motor won't get better than 13 mpg or so but I am around 10 now). I run load range 'E' tires and keep them inflated in the 60-65 PSI range. I have no SES light or codes stored. At 100K I replaced plugs, wires, pcv and fuel sock.

    I have read other posts regarding the possibility of bad O2 sensors in other threads but I don't know for sure if that can be a indicator with no code. Are my conditions enough to justify O2 sensor replacement (at a high cost) with no SES light?

    Thanks for any suggestions.
    Erik

    2002 Camaro SS LS1 / 1 of 147
    2004 Suburban 2500 HD 8.1L

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    Senior Member ss~zoso~ss's Avatar
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    run some fuel system cleaner through it and beat the snot outta it for a day, see if there is carbon build up, Seafoam is a great product, you can suck it in through an intake manifold vacuum line and stall the engine with it, then u let it sit as it eats the carbon from the cylinders then you start it up and it should smoke like a bastard, i did this on my 90 volvo 240 with 200k on the clock and it smoked like crazy, do a search to find out more

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    Need Sand ??? Naf's Avatar
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    AHHHH!!!!

    Its a bit more that just injector cleaner for him...

    He has about 106k on the odometer...You need a full day in my books to do the job right...Its starts with a simple engine oil flush...

    Then i would turn my attention to your MAF sensor, a good clean with soft hands and WD 40 would do the trick...STAY AWAY FROM THE RESISTORS...If damaged you will have to replace completely...

    Then i would pop off the throttlebody and give it a good scrub as well a few squirts of WD40 and carb cleaner into the intake manifold...

    Later if you still have the energy i would remove the plugs and replace with Bosche...And the sparkplug wires probably need a good change as well...

    This will jump you back to where you aught to be....

    have fun

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    Member erikzola's Avatar
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    Hey Naf thanks for the comments....

    At 100K I replaced the plugs and wires and since have added some fuel injector cleaner a few times with no solid results. I will take a look at the MAF and Throttlebody as you suggested and see what happens.

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    JOSEY FUCKING WALES! Frankthetank's Avatar
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    wow....this is probally gonna make me sound like a tard but i didnt know they still put bigblocks in anything

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    Junior Member STL2SLO's Avatar
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    Make sure you check for a vacuum leak.

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    Member erikzola's Avatar
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    Quote Originally Posted by Frankthetank View Post
    wow....this is probally gonna make me sound like a tard but i didnt know they still put bigblocks in anything
    Yeah, I think 2004 was the last year. Only available on 2500 suburbans and larger pickups. When it runs right it's great.....

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    Member erikzola's Avatar
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    Quote Originally Posted by STL2SLO View Post
    Make sure you check for a vacuum leak.
    No obvious signs of one that I can see. Even as of now no SES light or any codes. Any further thoughts?

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