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Prognosis (45 Days)

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by TheEmissary, Jul 15, 2000.

  1. TheEmissary

    TheEmissary Registered Member

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    Location:
    Houston, Texas
    Since 5/30/00, my Blazer has been averaging 10.2 MPG. This was before the mandate of cleaner burning fuel in the Houston area, and here's what I have experienced:

    Last summer, I was averaging around 11.5 MPG, and this was with "nonreformulated fuel". The only things that resulted in a "Bonnie Crisis" was a fragged starter, a carb swap, and replacing distributor parts.

    For the past 45 days, here's the average reading from my temp gauge (with a 180 thermostat):

    200 degrees

    70 mph cruise (A/C on): 205
    70 mph cruise (night): 180

    I have changed the fan clutch, and there was substantial improvement. The cruise temp used to be 220 @70 mph (A/C on), and now, around 200 is OK.

    I cannot go above 10.5 MPG for the past 45 days, and recently, I changed the tranny oil and filter. So far, no change, no improvements. Right now, I owe MasterCard $350.00 in fuel bills, and it seems I'm at a dead end.

    My mom didn't take the news seriously; she has contemplated filing criminal charges. Personally, I do not like rehashing a scene from Pulp Fiction or Jerry Springer every evening, and hope that I expect 12.0 MPG again. I hope that Gore should lose this November.

    The Emissary
    1981 K5 Blazer 4 x 4
    305 (LE9)/THM350C/NP208

    Other vehicles:
    1975 Nova
     
  2. Jason73K5

    Jason73K5 1/2 ton status

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    Why'd you swap carbs? And what kind were they? The new carb is most likely the cause of your drop in mileage, though one mpg isn't much of a drop in mileage. Another way to incrase mileage might be to drop your cruising speed, 4X4's were never meant to be high speed cruisers and I'd bet that if you stay closer to 55-60 that your mileage will improve. If you've got an AFB style or Holley carb, it might be worth it to switch to a Q-Jet, as these were designed for good fuel economy and actually get better mileage that a 2 barrel will. One of the easiest ways to improve economy is to just drive less aggressively(not much fun though). If you're in a warm climate, pull off your top and tailgate, you'll drop a few hundred pounds which should help a bit.
     
  3. DBLAZER

    DBLAZER 1/2 ton status

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    Try the Jacobs mileag master ign. kit. It is supposed to improve the mileag. I have a few buddys who have had good luck with that.

    89 w/DANA 60-Corp 14 w/5:13s n Detroit's. 4"lift 2" body. NEW AtlassII ordered 5-15-00. 38" sx's -
     
  4. rocko

    rocko 1/2 ton status

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    I'm not voting for "ozone man" .. He want's to do away w/ all internal combustion engines. We'll all be driving electric cars... and watch out for the so called "clunker" bill he want's to pass.. All pre 1987 vehicles are subject to be turned in to be scrapped since they pollute the air.
    Bush all the way. !!!!!

    It's better to Have IT than to not need it, Than to Need it and NOT HAVE IT !!!!
     
  5. TheEmissary

    TheEmissary Registered Member

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    I swapped my OEM Quadrajet with a similar one, a parts house special sold through Holley. The original Quadranator had a shot throttle shaft, and had to settle with a parts house replacement.

    The Emissary
    1981 K5 Blazer 4 x 4
    305 (LE9)/THM350C/NP208

    Other vehicles:
    1975 Nova
     
  6. MudRebel350

    MudRebel350 1/2 ton status

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    VOte Bush all the way. Like father like son. Get the democrats out of the white house.
     
  7. TheEmissary

    TheEmissary Registered Member

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    Here's my JT: Bush (after November) shouldn't make the same mistake like his dad. Right now, every metropolitan area targeted by the EPA has to market RFG, and the 87 octane that I dump in the tank is all I can afford.

    Tomorrow morning, I will hit the local Pep Boys for a Hayden 3710 electric fan, and install it behind the radiator. The fan will be wired into the A/C circuit, since this is where the source of the unburned fuel is. Here's how it goes:

    The 305 gets 20" Hg when I hook a vacuum gauge, and the carb screws were turned 6 times CCW. I have set the static timing at 6 BTDC, but throughout the past 45 days, all I end up with is 10 MPG average. Sometimes, at the light, I would rev the motor (in neutral), and black smoke "puffs" are visible. I might consider installing a heavier spring on the accelerator pump circuit, but I have opened up the carb a few weeks ago and did the following:

    float adjustment (1/4" from top)
    installation of a cylindrical plastic baffle (where the APT sensor normally resides)
    secondary door adjustment (3/4 to 1 turn setting CW)

    Recently, I changed the tranny oil and filter, and noticed that the oil was between red and brown (glittering metallic flakes and some worn bushing material). I thought this would result in a 1.2 MPG increase, but had to do it before my planned 700 swap.

    When I salvaged the 700 from a derelict 1985 Jimmy, the tranny was a 1990 core (oil still reddish-pink, with few metallic particles). Recently, I installed the TCC harness from the donor Jimmy, and one thing that I will do is to allow the lock-up to operate in 4th gear only (after consulting with a GM service manual).

    I have the following: tranny X member, adapter, and dust cover. The stock NP208 will be reused, and I believe that the 700 swap would benefit a little.

    It seems that my 350C tranny might be numbered.

    The Emissary
    1981 K5 Blazer 4 x 4
    305 (LE9)/THM350C/NP208

    Other vehicles:
    1975 Nova
     
  8. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Black smoke is rich dude...thats your MPG problem right there. Put smaller primary jets in to cure that. 6deg of timming seems a bit low to me. On my 79 350 I run about 10 deg for the most power and understand the more efficeint it run the better the MPG. Try running 8 deg and see if you hear any ping and speaking of ping you got a knock sensor distributor. I'm not sure how you test them but do test it. If it malfuntions and incorrectly senses a knock/ping then it will retard the timming and you loose power.

    Diging it in the dirt with my K5's
    Grim-Reaper
    http://grimsk5s.coloradok5.com/
     
  9. JimmyDie6.2

    JimmyDie6.2 1/2 ton status

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    just keep on voting democrat....we'll all be drones shortly.
     
  10. TheEmissary

    TheEmissary Registered Member

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    I set the static timing, using the core support label. 8 degrees BTDC might be excessive for an ESC system, but good for a 350.

    The jets in the "remanufactured" Quadrajet are 72s. I have never had a problem with #72 jets, but when I dismantled the carb last month, I documented the #s of the jets, primary/secondary metering rods, and rod hanger. In some cases, I would refer to the Rochester Carburetors book.

    I ended up swapping a 160 thermostat, and there was a 10 degree decrease.

    BTW, when installing an auxillary fan, is it best to wire up a toggle switch? I used the A/C circuitry, but I have blown 2 fuses. Would a relay eliminate blown fuses?

    The Emissary
    1981 K5 Blazer 4 x 4
    305 (LE9)/THM350C/NP208

    Other vehicles:
    1975 Nova
     

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