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6.451612 MPG on a 355 TBI..WTF? ****Update*****

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by unsane, Feb 3, 2003.

  1. unsane

    unsane Guest

    This gas mileage thing is starting to get out of hand! I just dont understand what the hell is going on! Here is what I have changed and or done to try and remedy the problem.

    New o2 sensor, new plug wires =runs worse now. I am about to get out the 12 gauge and start target practice soon.

    Well I changed the o2 sensor tonight along with new wires(found a burnt one) But guess what? Now it runs like a total POS. My cub cadet runs twice as good. Any ideas before I get out the 12 gauge and start the mayhem.???????
    1. Adjust timing
    2. new fuel filter
    3. injector cleaner
    4. removed beads from cat(thought it was plugged)
    5. DROVE SLOWER
    What gives on this? I would be better off driving a top fuel car to work and back. I am not asking for much maybe 15 MPG or something. Everything is stock except: 0.030 over bored, edelbrock tbi intake, stainless valves. New motor has approx 2k on it. 10 bolts and 31's. Can someone please help me find out where my fuel is going? I just made the ALDL cable tonight so I might give that a try tommorrow. Thanks in advance for the help.
     
  2. schmuck

    schmuck 1/2 ton status

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    Re: 6.451612 MPG on a 355 TBI..WTF?

    i think 15 mpg is too much to ask i get about 8 city 10 hwy
     
  3. Bubba Ray Boudreaux

    Bubba Ray Boudreaux 1 ton status

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    Re: 6.451612 MPG on a 355 TBI..WTF?

    What gears are you running? I pulled almost 13 this weekend, but that's on a tired engine, 3.73 on 35's.
     
  4. unsane

    unsane Guest

    Re: 6.451612 MPG on a 355 TBI..WTF?

    I would have to disagree. 15 mpg with a new motor. Maybe if I were runnin 39 inch boggers and 4.11s or something, but this is stock TBI were talkin here.
     
  5. unsane

    unsane Guest

    Re: 6.451612 MPG on a 355 TBI..WTF?

    I guess 3.08's or whatever is stock on an 89. I have never changed em. Never have the money, to busy using it to buy GAS.
     
  6. Bubba Ray Boudreaux

    Bubba Ray Boudreaux 1 ton status

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    Re: 6.451612 MPG on a 355 TBI..WTF?

    On my trips back to Oklahoma, I've averaged about 16 with a time or two hitting 18.
     
  7. zakk

    zakk 1/2 ton status

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    Re: 6.451612 MPG on a 355 TBI..WTF?

    what is your total timing? I picked up about 2-3 MPG just getting my total timing under control.

    also, is your O2 sensor replaced? that might be a culprit, but at 6 mpg, you got some major problem somewhere, IMHO.
     
  8. unsane

    unsane Guest

    Re: 6.451612 MPG on a 355 TBI..WTF?

    I dont really now how to set total timing. Can you elaborate?
     
  9. zcarczar

    zcarczar 1/2 ton status

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    Re: 6.451612 MPG on a 355 TBI..WTF?

    On your TBI you need to disconnect the timing advance wire to set the timing, disconect that and set the timing to 0 degrees. The computer adjusts the rest. O yeah I get around 7-9 mpg with my 350 TBI/4.10's/35's, I have 12k on the reman engine also.
     
  10. morphed86k10

    morphed86k10 1/2 ton status

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    Re: 6.451612 MPG on a 355 TBI..WTF?

    Yikes! I got 10 in the K30 with 33's and 4.10's, with a 454 and an auto. On the highway of course. My truck now should do a bit better.
     
  11. Blazer1970

    Blazer1970 1/2 ton status

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    Re: 6.451612 MPG on a 355 TBI..WTF?

    Sounds like it is running in cold start mode all the time. Can you smell the raw fuel in the exhaust?
     
  12. Bubba Ray Boudreaux

    Bubba Ray Boudreaux 1 ton status

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    Re: 6.451612 MPG on a 355 TBI..WTF?

    </font><blockquote><font class="small">In reply to:</font><hr />
    O yeah I get around 7-9 mpg with my 350 TBI/4.10's/35's, I have 12k on the reman engine also.

    [/ QUOTE ]
    Would you be offended if I told ya that kind of mileage sucks? /forums/images/graemlins/grin.gif
     
  13. Thunder

    Thunder 3/4 ton status

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    Re: 6.451612 MPG on a 355 TBI..WTF?

    I have 350 TBI 3.73 33" tires no lift. I get 15-16 mpg combination average city/ highway driving. Most people I know who have a TBI get fairly good MPG (for a truck) Even my buddies 3/4 ton with 4.10s and a 14sf gets 15 mpg on the highway
    There is definatly something wrong.
    The Ecm may be running in Closed loop because of a bad sensor. Or it may be running in back up mode because of an ECM failure or mulitple sensor failures. Both modes will give bad fuel milage. It was designed this way so the owner would get it fixed.
    You really need to get a scanner on it and check it out.
     
  14. BigRed89

    BigRed89 1/2 ton status

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    Re: 6.451612 MPG on a 355 TBI..WTF?

    Zakk has a really good suggestion of checking out the O2 sensor. If you haven't replaced it, don't even worry about looking at it, just get a new AC Delco unit and put it in. Also, do you have the stock exhaust manifolds and tubing? The placement of the O2 sensor in the exhaust system makes a difference. I picked up 1.5 mpg just by moving the O2 sensor from the Y-pipe junction, to the driver's side exhaust header. Currently in my '89 Sub I have a 383 / TH400 / 3.73s / 35" tires and I get 9.5 mpg city and highway combined.
     
  15. caryhenry

    caryhenry Registered Member

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    Re: 6.451612 MPG on a 355 TBI..WTF?

    Just got a question for everyone... What kind of gas mileage should I expect from an 85 305 3.08 31x10.5x15
     
  16. 90K5

    90K5 1/2 ton status

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    Re: 6.451612 MPG on a 355 TBI..WTF?

    Maybe your calcluator is broken???
     
  17. zcarczar

    zcarczar 1/2 ton status

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    Re: 6.451612 MPG on a 355 TBI..WTF?

    Yeah I know my mileage sucks ass, I was getting 5 mpg a few months ago, but the previous owner screwed up a lot of stuff when he put the engine in and I dont know what is wrong with it. Hell even the techs i work with cant figure it out. Maybe I need to move my 02 sensor.
     
  18. txbartman

    txbartman 1/2 ton status

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    Re: 6.451612 MPG on a 355 TBI..WTF?

    In days past, my rig was 305 3.73s 32x11.5 BFG ATs with 700R4. I used to get around 9-10 around town and 10-12 on the highway. But I also had a carb in pretty bad shape.

    Most recently I improved to 383 4.56s 35x12.5 BFG MTs still with the 700 but a new carb. I went from around 160 HP in the 305 to 420+ HP in the 383 and my gas mileage is still around 9-10 in town.
     
  19. Swanson52

    Swanson52 1/2 ton status

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    Re: 6.451612 MPG on a 355 TBI..WTF?

    My K20 with 36 inch Swampers, 4.10's, and a box-stock 350/400/208 just knocked down about 13 on a road trip last weekend. I have been considering an upgrade to TBI and would expect about a 3 mpg gain with it. Are both your injectors firing?
     
  20. sled_dog

    sled_dog 1 ton status

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    Re: 6.451612 MPG on a 355 TBI..WTF?

    my stock 305 engine 84 with 3.73s and 33s got like 6-8mpg city. Never did highway cause she was too unreliable for distances.
     

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