Problem returns

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Wes Harden, Mar 27, 2019.

  1. blazer74

    blazer74 Member Premium Member

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    The return line is off the pump. My 74 didn’t have the return installed.

    Never had a problem for many years like 25 of them.
    Then it began, studder stammer, hard start hot, bucking.
    The hotter out the worse.

    I tried the non E gas, little better at best, so I’m not sold on the non E thing.

    Tried high volume EDL street pump no help ( no return line.)

    Changed Distributor, rerouted fuel line away from block, left the gas cap off, No Help.

    Last thing was to install a Wix 33041 fuel filter up at the carb inlet as a test. Has the 1/4 inch return on the filter with 3/8 inlet and outlet. My K5 did not have the return setup so I used the 5/16 vapor line that normally goes to evap can for the return. Gas cap is vented to prevent the return fuel from pressurizing the tank.
    After I did the fuel filter trick I did not experience the same problems, ran like it did years ago.

    It was for a short time due to a blown rear pinion. Been in the garage for a year for some work but it sure seemed like a fix.

    I am confident it’s a vapor lock problem due to modern fuel.

    I can’t speak for your issues but it’s worth a shot. Even though you have a return at the pump, you could try moving the return to the inlet of the carb just to test.

    Just a note I have installed a fuel psi gage at the inlet to the carb and every time the problems happen the fuel psi drops off to zero. After the filter/ return test the fuel psi never drops to zero. IDK but until I get back on the road that’s all I’ve got.

    Bye the way the return in the filter is a .060 hole.
    The pump still maintains 6 psi at idle.
    Best guess is vapor lock from the pump to the carb.

    I will also note that if I let the engine idle in the drive way on a hot day the clear fuel filter I installed would go almost dry and you could see the fuel splashing through, although the engine would never quit.

    If I put a water hose on the pump the fuel filter would fill back up to half way so it’s definitly heat related.
    That’s my experience, never had up hill issues and am not responsible for your results. Just IMHO.

    B74A26A3-7160-431C-AC41-89F862D1548F.jpeg
     
  2. Wes Harden

    Wes Harden 1/2 ton status Premium Member

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    Well, I finished the electric fuel pump install, along with a new AC Delco complete distributor. Test drove today, in 101* temp. Up and down all the hills around my home. Ran great no coughs sputters or stumbles.
    Seems down on power, I had my foot all the way down a lot.
    Got a little warm temp guage at middle, normal below 1/4. Did have the AC running. No over heat.
    Trans temp in pan was 210ish even locked up in 3rd and 4th.
    Going to get a 10" electric fan for ac cooling. Temp untill I do winstar fans.
    I set the timing at 9* tdc ported vacuum.
     
  3. Wes Harden

    Wes Harden 1/2 ton status Premium Member

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    Added a 10" Hayden 650 cfm fan to condenser, with relay. Didn't have time to find an A/C power signal so I toggle switched it, figure I will hear it if forget to shut it off.

    IMG_20190611_160823.jpg
    Nothing like a good crimp
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  4. 6872xtc

    6872xtc make mine modified Premium Member GMOTM Winner

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    I would bump the base timing up. I am at 4700' elevation and I have my 406 SB set to 12*.
     
  5. JoshHefnerX

    JoshHefnerX 1/2 ton status Premium Member

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    Fans wont do much to cool down your truck above about 50mph, can even block air flow. Were you getting warm at speed or putting around?
     
  6. imiceman44

    imiceman44 Hoarder extraordinaire Premium Member

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    You can hook it up to the compressor wire.
    Every time the compressor comes on the fan comes on.
    You will never forget it on
     
  7. Kain

    Kain 1/2 ton status Premium Member

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    check your voltage with it running see what it is when hot
     
  8. Wes Harden

    Wes Harden 1/2 ton status Premium Member

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    Pre 10" fan, I was get warm at speed driving up and down all hill around my house, as fast as I was able. Didn't over heat, but gauge was higher than I have seen it since reviving from moth balls in December.
    electric fan is for A/C at low speed. Heading to Lake Havasu today, so I expect to be driving slow in the heat. Boat ramps exc.
    In 1987-88 I worked for GM as a tech in Lake Havasu. We had a customer with a new Suburban, the A/C would not cool the center regulator down past 70 in the summer after being parked in the sun all day. Our solution was add a small fan. 2 months later GM issued a TSB @ poor A/C performance in hot climates with part numbers for retro fit fan. Next models came equipped with fan.
     
  9. Wes Harden

    Wes Harden 1/2 ton status Premium Member

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    Drove the truck 260 miles from CA, to Lake Havasu, late last night. Ran great cruised 70+ in 4th 65+ uphills in 3rd. Seems to perform better in coolesh weather, 80*+ last night.
    Still want more prefomance at 45 to 60 mph.

    The issue is definitely fuel delivery. I turned off the electric pump and problem occurred almost immediately.
    In the near future I will check the pump rod and cam lobe.
     
    Last edited: Jun 13, 2019 at 2:12 PM
    Kain likes this.
  10. Wes Harden

    Wes Harden 1/2 ton status Premium Member

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    So my timing marks are off, engine timed at 9*. I had to take timing out. My Brother was riding in truck with me and he could here it ping, I could not. Truck runs much stronger and cooler. I don't have a clue what the timing is now. I timed it by retarding, test drive towing boat, and my Brothers ears. 2 adjustments later is like the truck I remember b4 trans gave up and I parked it.

    I am guessing you mean voltage at the ac clutch coil? If so I hope I will find low current. Drive home A/c was working good, meat freezer, I switched from max to normal, around Needles, and no more cold. Stopped in Needles and the clutch disc was cooked, in 2 pieces. :mad: Oh well hot drive home. I will redesign the power circuit for the coil when I replace it. When I bought the truck in 2000 the disc was fried, fixed it once, year later burned up a second time. A re-manufactured A6 worked till this weekend. Now I am concerned that during high ambient temperatures the high side pressures are causing the disc to slips, and not low electric current.
     

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