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Thread: 86 Chevy C10 Dual Fuel Tank issue

  1. #1
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    86 Chevy C10 Dual Fuel Tank issue

    I just bought a 86 C10 with dual fuel tanks & a 305. It ran great however it did have a little (2-3 second) engine ping when taking off or goosing the throttle in park or in gear. This is a machanical fuel pump style, not electric fuel pumps in each tank. I was told the fuel selector switch was bad and you could not switch over the tanks and it was using the passenger (right) side tank. I got it home and with the key on/engine off I hit the switch on the dash to switch it over to the left tank. I heard the valve "move". It only made noise for a split second, maybe two. In the past any dual tank chevy valve (86 and older) the valve would open/close for several seconds (5 sec or more-usually) The gauge went to full and I monitored both tank levels to verify it actually switched over to the left and was drawing from there as well. By the time the left gauge was reading half full the engine developed a dead miss. I put new Champion plugs & wires in it as well as a distributor cap & rotor--no change miss is still there. I replaced the thermostat and adjusted the timing to 4 degrees as recommended.
    Engine runs great at idle, however when you put it in gear it was severely under powered and didn't run very good. I don't have very good throttle response after 1/4 throttle. If I floor it , it just looses power or very very slowly builds speed and takes forever to gain 3-5 mph. Meanwhile the "choke" light on the dash is lit up and stays on. I can adjust the timing and get it running good for highway speeds but it suffers on the low end, and vice versa. When I do this the miss goes away except when the timing is close to where it should be then it returns. I have replaced the fuel filter and the fuel pump, with no results/improvements.
    Is it possible that the fuel tank valve is not opened all the way for one tank or the other? I did not have this problem prior to switching the tanks.
    Truck is in great shape and tanks look brand new so I don't have any leaks anywhere on the fuel tanks. Is it possible that the crappy almost 1 year old fuel caused a problem withthe carb. The carb has the 2 wire connector at the top right side of the carb.
    Any help or info would be greatly appreciated.

  2. #2
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    um i had an 80 with dual selector and it would "switch" over to the other tank, read full i`d drive a while then poo she`d alost die run bad couldn`t even move, would stall when try to move, tested the switch under truck, replaced it and then it was good figured the solenoid was week in the selector and would switch then creep closed or default to the other tank, not saying its the same deal with you, just an experience i had,

  3. #3
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    have you switched it to the other tank? put more gas in the driver side? have you verified proper function of the choke?
    Joe
    89 K2500 Chevy, Wee-Oh-five 294K miles
    1962 Scout 80 parts I guess
    1966 Scout 800 resto job
    2005 Chevy 2500HD Short cab long box DURAMAX
    1996 P30, 6.5 NA Mac Mobile
    whole lot of buicks

  4. #4
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    Choke is working correctly when cold start and warmed up. Yes, I have switched over the tanks.
    That's when this mess started, when I switched over to the left tank and used the fuel in there. There is fuel in both tanks, doesn't matter which one I use it runs like **** as soon as you put it in gear and give it the gas. If i drive it like I'm 90 years old and use just 1/4 throttle or less it's not as bad. But it takes forever to get up to speed. At cruising speed not much problem until I come to a small hill or incline.
    I'm going to bypass the electri fuel switchover valve and hook up the tank direct to the fuel pump so I know if the valve is partially closed.

  5. #5
    Senior Member 1979_4x4_Plow's Avatar
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    is there any kind of filter in the tank that might be restricting the flow? my girlfriends car was having a miss and back firing, and would lose power and act like transmission was taking a ****. changed the 2 month old fuel filter and it worked fine. it is starting to get same problem again. i think her in tank filter is dirty and restricting flow. i would think there would have to be a filter of some sort in the tank to keep all the garbage out of the lines.

  6. #6
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    There is a very fine mesh screen filter in the tanks at the fuel pick up.
    I don't believe that is the problem.
    I'll update you after I bypass the fuel valve on Tuesday. I am hooking the fuel line and the return direct to the fuel pump for the right tank. If it straightens up then I know the fuel valve is not 100% open/switched over as I suspect is the problem. I just don't want to pay 100.00 for the valve if I do not need it.
    I am also replacing the choke thermostat too see if the choke light on the dash will go out.

  7. #7
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    OK-- I pulled the right side fuel line bypassing the fuel switch over valve and hooked it directly to the fuel ine to the mechanical fuel pump. It is a lot better but not 100% I am going to pull the return line and hook it up direct to the fuel pump as well, bypassing the fuel valve. The choke light is still on and the throttle is not kicking down to normal idle as the choke is not fully opening. I am putting a new choke thermostat on it later this week.
    I will post my progress as I work on it.

  8. #8
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    I got the choke light off. The connector next to the oil pressure sending unit was half off. I must have bumped it when I was setting the timing or replacing the plug wires.
    I still have some issues that it seems to have no/less power than normal thru the throttle range.

  9. #9
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    I found a vacuum line disconnected at a "y" that feeds the EGR valve. I reconnected it and the truck is running better.
    When the engine is cold it goes like **** and has plenty of power. It still doesn't have normal power when warmed up but it is much better.
    I'm going to re-check the timing and adjust if needed.

  10. #10
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    Dual gas tank issue - 83 Silverado

    Wish I had joined this discussion earlier. My time is limited in working on my old truck, so I took it to my mechanic when my left tank seemed not to work, making the truck run very rough while pouring out black smoke. There was also a pressure build up, causing the gas to shoot out, under the gas cap! Never heard of such a thing. The right tank works just fine. Also, the vapor cannister disintegrated, with gas pouring out under the front end; I replaced that via Autozone. Mechanic is good but could not find a new diverter valve, which he said was the problem. (Seems like the part could be found SOMEWHERE.AAA) Anyway, he direct-connected my passenger side tank now, so I have a useless left tank but runs like a new truck with the right tank. This is a low mileage (87K original) truck, so it is a shame not to have access to all the gas supply, even though I don't make many trips where I don't have plenty of gas stations. Hope Dragonfly has success in fixing his dual tank business.

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