1986 K10 Canister/Dual Fuel Tank Question

[soccer8yanks]

To start I live in DE and classic tagged vehicles still have to pass inspection the very first time they are tagged (my situation).  That being said I have two separate problems.

The first problem is I keep failing the fuel tank pressure test.  The last time I took it through the inspection lane the inspector said that my charcoal canister need three lines coming from it and I only have one (he said that's why its failing the pressure test).  Does anyone have a diagram of what the lines are and where they go?  Found a few diagrams of different year K10's jus couldn't find an '86 and wasn't sure if other years were the same.

The second problem (which I don't really need fixed for inspection but would like to have it working) is that when I bought the truck the previous owner had disconnected the second tank as it was all rusted out.  The gauge was working (and I assume the switch was also) with just the one tank, when I hooked up the new second tank, the gauge completely stopped working all together, no matter what tank I switched it to.  Any ideas of what went wrong there?

Any insight would be appreciated.

[rich weyand]

What does the gauge read?

[soccer8yanks]

What does the gauge read?

empty

[rich weyand]

Empty is zero ohms, which means the sender wire is shorted to ground.  Look for some place where your messing around shorted the wire to the frame.  What kind of switch is it?  Do you know if the sender wire is switched by the valve, or is it switched by the tank switch in the cab?  The short has to be between this switch and the gauge, because both tanks are reading the same thing.

[soccer8yanks]

This is what the switch looks like

[rich weyand]

OK, that looks like the reversing switch, which means that switch is hooked to +12 and ground, and then two wires go to a motorized valve on the RH frame rail in front about at the back of the cab.  The switch reverses the wires, which is what powers the valve motor one way or the other.  If you look under the truck along the inside of the fram rail you should see the valve.  It should look like this picture and have 5 wires to it.  Two are the wires from the switch that power the valve motor.  The three are 1) tank sender #1; 2) tank sender #2; the wire back to the gauge.  This last wire is the one that is shorted to ground somewhere.  This should be a pink wire that goes all the way up to the engine compartment and goes through the firewall on the firewall connector.  In the interior it will again be a pink wire that goes from the firewall connector directly to the instrument panel flexboard connector.  It's one of the corner wires of the connector, and the only one that is pink -- the others are black, light blue and light green.  You need to follow that wire and find the short.  You can pull the connector from the back of the instrument panel and use an ohmmeter to check the connectivity to ground of the pink sender wire.  If it is shorted, it is shorted between there and the valve back on the frame rail.  If it reads 20-30 ohms, then there is something rong with the gauge or the instrument panel board.

[soccer8yanks]

ok thanks, I will check all of that... any idea on the 3 connections from canister to fuel tanks??

[rich weyand]

3 connections?  One line in the vacuum diagram off the canister says "to fuel tank".  I know there is no 9-port tank selector valve, just 3-port and 6-port (for the return), so I am assuming they simply "Y"ed the vacuum line back by the selector valve and connected one to each tank.  These exist to scavenge air from the tank when the outside temp increases and vapors would otherwise be pushed out of the filler cap.  The "pressure test" is really a vacuum test.

The other two lines on the canister should be the vent and the line to vacuum source.

Believe it or not, Classic Industries has the correct emissions label for the 1986 2-door with 5.7l here: http://www.classicindustries.com/truck/parts/g2559.html.  This label includes the vacuum map and should be on the radiator core support.

[bd]

5/32" port to carburetor ported vacuum, 1/4" port to manifold vacuum (often teeing into the PCV valve plumbing), 5/16" port to fuel tanks and ~3/8" shrouded vent port to atmosphere.

[Irish_Alley]

and welcome from maryland/delaware your picture looks like its from dover. cant remember where that neighborhood is but reminds me of Dover at least. we just got another member from kent Sussex line. im about in the same area as him

[Irish_Alley]

lol after doing a little stalking i just click your profile i see you are form dover, scary

[soccer8yanks]

thanks all for the responses, my dad looks at the parts truck we have and we are gonna take the hoses and canister off of that... then will use rich's info to try and figure out the dual fuel tank/gauge problem... pm sent to DE guy