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TBI pump wiring question

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by BadDog, Dec 15, 2001.

  1. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Ok, finally got some time to finish the fuel system. Only thing left is to power the fuel pump in the tank. Problem is, I can't figure out where it connects into the harness. The only schematic I have is for a 90 "C & K series" and it seems that it is not quite the same as my 89 Sub harness. Anyway, according to my harness, there is a tan/white wire that should go to the pump. I just can't find it in the harness. The color codes for the pump relay in the schematic don't match reality exactly, but it looks like there is a pink/black going to the oil pressure switch, and then to a 20A fusible link where it becomes tan-white. Unfortunately, it disappears into that god awful wiring "trunk" stuffed between the back of the block and the fire wall and I can't figure out where the tan/white emerges. Should be a plug hanging out somewhere.

    Anyway, just thought I would throw this out in case anyone happens to know off-hand. I was running out of light (and getting cold) so I called it a night. I'm sure I can find it tomorrow with better light. I just hate digging around back there since you have to work your way though layers of stuff just to get to the harness trunk and then open it up...

    After this, work out the upper radiator hose and tie something in for exhaust and it should be up and running! Now if I can just find some good 40"+ tires cheap. [​IMG]

    Russ

    85 K30 CUCV, 350 TBI, TH400, 205, D60/C14, 4.56 Locked
    Some day: 4" lift, 44" tires, massive cutting, shorter wb and rear overhang.
     
  2. pcorssmit

    pcorssmit 1/2 ton status

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    This is from the '88 R/V wiring diagram:

    From the fuel pump, the wire goes to the bulkhead connector, circuit 120, it is on the smallest of the 3 connectors that make up the bulkhead connector, and is tan/white. On the other side of the connector (inside the truck), it goes to the hot fuel handling module, and also connects to the other side of the bulkhead connector, where it comes back out in the engine compartment through the largest of the 3 connectors (the terminal is on the outside edge of the connector, in the middle). From there it goes to a splice, with one wire going to the fuel pump oil pressure switch, one to the fuel pump relay, and one to the ECM (pin B2). All these wires are tan/white.

    Hope this makes sense (wish I could scan it).

    Pete

    '83 K5, 350 TBI (ex 6.2), 700R4, NP208, Dana 60/14 bolt, 4.56s, Detroits, 3" lift, 15-39.5x15 TSLs
    '97 Dodge 2500 4x4 CC LB Sport, Cummins 5 spd
     
  3. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Ok, how about this. What/where is the "hot fuel module". Anyone got a "parts locator" manual for a late 80's TBI C/K series? Looks like the tan/white ties into it on the way to the tank. The only place I can find the tan/white coming out of the wiring trunk is going into the fuse block. Oh well, guess I'll keep looking...

    Russ

    85 K30 CUCV, 350 TBI, TH400, 205, D60/C14, 4.56 Locked
    Some day: 4" lift, 44" tires, massive cutting, shorter wb and rear overhang.
     
  4. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    LOL, I was posting asking where the "hot fuel module" could be found while you were typing. <img src="http://coloradok5.com/forums/images/icons/laugh.gif">

    Ok, that helps. Thanks.

    Just my luck, I didn't get the other harnesses on the bulkhead connector. Just the engine compartment section. The smallest is the outside (next to the fender) and is the rear chassis harness (makes sense). Now I know why I couldn't find the connection. <img src="http://coloradok5.com/forums/images/icons/crazy.gif"> I thought it would have a connection coming off the pump relay and jumping to the rear harness. Didn't realize it actually went through the bulkhead.

    I guess I'll have to patch in at the hot fuel module or add the missing connector to my rear chassis harness. To save me pulling the block/bulkhead connector and working it all out, can you tell me what pin of the chassis connector that it runs on? A full pin-out would be great (if you don't mind) so that I can check to see if something else moved. Sorry to ask you to go to so much trouble. I need to find one of those CDs that have all the service manuals on it (or borrow one to copy).

    <edit>
    Ok, my schematic (which doesn't match colors exactly with my '89 harness) shows the HFM with tan/wht, brn, blk/wht. There is no plug in my cab harness (from the same truck as under hood harness - 89 Sub TBI) with those colors but there is a small 6 connector (pins, not blades) with pink instead of brown. I figure that is likely it.

    I'll run a continuity test on it to verify but I wanted to add, just what the heck is a "hot fuel module"? Is it important? Looks like I didn't get it with the cab harness (assuming that is the right plug). [​IMG]
    </edit>

    Russ

    85 K30 CUCV, 350 TBI, TH400, 205, D60/C14, 4.56 Locked
    Some day: 4" lift, 44" tires, massive cutting, shorter wb and rear overhang.<P ID="edit"><FONT class="small">Edited by BadDog on 12/16/01 04:42 PM.</FONT></P>
     
  5. pcorssmit

    pcorssmit 1/2 ton status

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    OK, did somemore looking in the books.

    "On a 7.4L engine or a G Van with a 5.7L engine and all other 5.7L engines over 8500 GVW, a fuel module will override the ECM two second timer and the fuel pump will run for twenty seconds and then shut "OFF" if teh vehicle is not started. This circuit corrects a hot restrat vapor lock during high ambient tempertatures."

    Looks like the hot fuel module is only used in 454s, G vans with 350s, and 350s over 8500 GVW (ie 3/4 ton +). Assuming your harness is out of a 1/2 ton sub, you don't have one. If it is a 3/4 ton, it is located behind the dash, to the left of (from inside) and above the steering column.

    On a 1/2 ton the wire goes into the bulkhead connector, then (essentially) comes back out the other side (different part of the connector). Inside the truck there is a wire connecting between the two sides of the bulkhead connector, you probably wouln't be able to see it without pulling the fuse block. I suppose if you wanted to, you could remove the tan/white wire from the connector and run it straight to the pump. I don't have an '85 diagram, but I do vaugely remeber from my conversion having to switch around a few of the wires on the bulkhead connector, to make the '88 harness work with the '83 Diesel Fuse Block.

    Just for clarification, the '88-'91 Blazer/Sub/Crew Cab were reffered to as R/V models.

    Pete

    '83 K5, 350 TBI (ex 6.2), 700R4, NP208, Dana 60/14 bolt, 4.56s, Detroits, 3" lift, 15-39.5x15 TSLs
    '97 Dodge 2500 4x4 CC LB Sport, Cummins 5 spd
     
  6. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Ok, that matches with what I found (see my edit above). So, I'll probably just unclip the tan/wht where it goes in on the engine harness, add a spade connector, and run a wire to the pump.

    Do you have the info on the rear chassis pin-out? Or the front chassis harness (center bulkhead connector) for that matter. I thought they were all the same (generally just lights and such) on most years but after this, I have learned otherwise. If you don't have time, I'll just head to the library or dealership and see if I can find a bulkhead pin-out for my model. Unfortunately, last time I was there, they do not have the books for 89 R/V at the PHX library. Closest is 90 C/K Series...

    Russ

    85 K30 CUCV, 350 TBI, TH400, 205, D60/C14, 4.56 Locked
    Some day: 4" lift, 44" tires, massive cutting, shorter wb and rear overhang.
     
  7. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    I did a continuity on the tan/wht from the engine harness to the rear chassis harness. Looks like it comes out on the third to the bottom (out of 7). My old harness (85 diesel) has a 20 amp fusible link feeding in on that pin. Looks like it is rewire time...

    BTW, a great big THANKS for all your help on this EFI conversion. You've been a big help.

    Russ

    85 K30 CUCV, 350 TBI, TH400, 205, D60/C14, 4.56 Locked
    Some day: 4" lift, 44" tires, massive cutting, shorter wb and rear overhang.
     

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