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Fuel mileage ??

Discussion in 'Chevy Suburban Forum (GMC Yukon XL)' started by Treadnmud, Jan 26, 2012.

  1. murdog94

    murdog94 Epic Member 5+ Years 5000 Posts

    Nope 87 is going to give you the same milage. As to the plugs yeah the are actually most likely the platinums that are recommended for that motor, and the stuff on the tip is most likly carbon etc. Just gap them (to ensure they arent all worn out) and if they gap well and have a nice browned appearance then put them back in.. Another thing i did actually forget to recommend is a new fuel filter.. The injectors are not really serviceable in the 96-99 5.7L Vortec unless you want to pull the top of the motor off, and if you arent getting a misfire code then i doubt they will need it.
  2. phoebeisis

    phoebeisis Epic Member 5+ Years 1000 Posts

    My 1998 2wd 1500 Suburban gets 21 mpg on long-1500 miles one way-all highway trips New Orleans>Flagstaff AZ
    I set the cc to 67 mph on the interstate- but probably actually average 62mph because of road work(45 mph) and various towns and cities-
    and the 60 mph speed limit on Hy 287 in TX.
    Get 12-14 mpg in pure city short trip driving.
    You should do at least 17 mpg at 65-70 mph
    I have the 3.42 rear end-probably helps FE a bit-the elevation on that trip also helps-less air drag
    Charlie
  3. Treadnmud

    Treadnmud New Member

    The fuel filter looks fairly new, definitely not the OE filter. I will probably try running the engine off a pressurized injector cleaning solution before I pull any injectors. If they are dirty, I will be able to tell after that. Haven't checked the fuel pressure yet, still looking for my fittings.

    The plugs didn't have the classic light brown look that I am used to seeing. I would say more black and appeared to possibly be running a tad rich. I don't think the o2 sensors have been changed and I haven't looked at the MAF sensor yet.

    What else I am I missing that I should check?
  4. murdog94

    murdog94 Epic Member 5+ Years 5000 Posts

    I would recommend replacing the fuel filter (usually should be done every 20k miles) plugs i would go ahead and put a new set in when you do the cap and rotor. Make sure you check the PCV valve, and if you are feeling froggy i would pull the TB and clean it up with Throttle Body cleaner (Carb cleaner is not good for TBs) Get a can of maf cleaner and clean it up (never hurts) also air filter of course.
    And now you are talking about the injectors, i will say this. it is a central injector with poppets, with as i said requires pulling the upper intake off to service, and really there isnt much you can do to clean them up. As to the O2 sensors, if they arent kicking a code that means they are working in the proper range and dont need to be replaced.
    Also you only need a shrader vavle to check the fuel pressure (on the intake) you need to have at least 55PSI at idle, and the vortec motors you have to have 58 PSI for the motor to start. I would do a seafoam treatment before you change the plugs, also make sure you are running the corrent weight of oil and change it around 3-4K miles (on the 350 it seems to hurt the milage with dirty oil at least on the 8 of them that i have owned)
  5. Treadnmud

    Treadnmud New Member

    Sounds good. I have been out of he gasoline engine circuit for a while now. I guess things have changed a little. Lol. Running 5w30 I think in it and change it regular. Yeah, gonna give this thing a good cleaning and go from there.

    Came home to Mississippi for a funeral this weekend. The fuel mileage APPEARS to have improved after replacing the valve body.

    I have noticed that sometimes I have to crank the engine twice to get it to start. Could be low fuel pressure. No codes though.
  6. murdog94

    murdog94 Epic Member 5+ Years 5000 Posts

    Check the Fuel pressure, but there is a chance that the Fuel pressure regulator is going down hill. But verify since it isnt fun to change.
  7. janikphoto

    janikphoto Rockstar 3 Years 100 Posts

    Bad. The most efficient way of driving is with the converter locked. It is unlocked so the vehicle can stay in drive at a stoplight and not stall. However, the physical attributes of using fluid to transfer energy from the engine to the wheels is much more inefficient than having it hard-locked together. This is a dumbed down version of how an auto trans works, but it gets the basic point across.

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