Questioning myself on this fuel problem.

Discussion in 'GM Powertrain' started by aficio400, Nov 23, 2010.

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  1. aficio400

    aficio400 New Member

    Taking a butt kicking here. I have a 1987 3/4 ton Pickup since it had 12k on it and only have 69k on it now. It is a 454 tbi with a turbo 400 and the towing package. My grandparents special ordered it new.

    I have had fuel problems for a while. a few months back i moved the bed back and replaced both fuel pumps with the strainers. I also replaced the rocker switch for choosing the tank. the right tank was not working i was getting bad readings on the fuel gauge, and it was jumping. I have not added a second ground to the tank to make sure that is tight. the reason for that is years ago i would change the pump by dropping the tank and i wonder if i stretched the wire on inside the shield and possibly that is why the gauge was not working.

    So the other day i decide i want to look at the right side. i flip the rocker switch to the right side then crawled under the truck to test the voltage. I asked for a meter and was smelling a burning smell, when my son came over to give me the meter he told me that the truck was smoking inside. When i got in i did not see any smoke but i could smell it.

    Well guess what? the truck now would not start at all. I did test the pumps for noise using the test line on the fuel pump relay, and could hear both of them. I did find a bad ecm B fuse and a second one. but either one of them burning should not have created the smell. I did remove the dash bezel and dash and have been through the wiring and was not able to find any wires that look like they have heated up.
    When turn the key on i can hear the pump running, but when i got under it tonight i was easily able to use my finger to try to feel any flow and there was very little. I did not put a gauge on it to check for the 9 psi but there seem to be very little flow. I did disconnect the line at the TBI and did not get any flow there. I thought that the new filter i had replace may have been bad, i removed it and it was fine, with no restrictions.

    So not i am wondering if it is possible that the diverter valve may be causing some type of problem, and possibly the rocker switch was causing the smoke. I did not pull it yet.
    Any ideas would be helpful.
    thanks
  2. stephan

    stephan New Member 1000 Posts 100 Posts

    Welcome to the GM truck club Aficio. Since your son saw smoke in the truck & you could smell it when you got in, you have to find the burnt wires before you go any farther. You talk about checking the wires at the dash bezel, but did you check them at the switch? If the switch wiring or the "switch itself" is burned out, that may be why the valve is not working & it could be stuck inbetween because it didn't get switched all the way before the electrical burn/malfunction. The diverter valve is easy enough to check just by disconnecting it, but I believe your first problem to address is your burnt wiring. Also need more info on this ground wire that was questionable from the fix from months ago??

    BTW, I believe your TBI needs 12 psi not 9psi
    Last edited: Nov 23, 2010
  3. mfleetwood

    mfleetwood Moderator 1000 Posts 100 Posts

    Welcome!!!
  4. aficio400

    aficio400 New Member

    I will double check the switch in the tomorrow after work. With everything apart it will pretty easy to pull. Thanks
  5. silveradotrailblazer

    silveradotrailblazer New Member 1000 Posts 100 Posts

    Welcome to the club.
  6. aficio400

    aficio400 New Member

    Still taking a butt whipping here.
    Well I wish it was the switch, Changed it out and no difference, did need to replace a blown guage and ecm b fuse.
    And After i thought about it i pulled and replaced the fuel selector valve and bought a kit and took the time to replace the harness for it, i use solder on the joints and shrink wrap to keep it sealed. Tested it on the left tank and it started up and ran fine. The only problem is when i turned the ignition switch off the truck keep running, not dieseling but running, it did change rpm i think because of the computer, but i could give it gas and it was smooth, the accessories like the ac would not work unless i had the key on but the motor ran fine. HELP and ideas??
  7. stephan

    stephan New Member 1000 Posts 100 Posts

    Hey Aficio,
    It seems like this new problem started after your son saw smoke coming from the dash & you could smell something burning. You need to find out what was burning because I think it is what is causing your "new" problem with the engine running after you turn it off. It is maybe burnt wires giving power, or could be a burnt relay that is burned in "closed" position & supplying power.
    It is not the ignition switch, because if it was staying on, the AC would have worked, & since the accessories were not working when you turned the ign. off, this indicates switch is working. You must find out what was burning that caused all the smoke. I think this is where your problem is.
  8. aficio400

    aficio400 New Member

    I agree, my problem is that my Chilton schematics do not seem to be that good. I do not see any relays besides the fuel and ac. I will dig around on the internet and see if i can find some more info.
    Thanks
  9. stephan

    stephan New Member 1000 Posts 100 Posts

    I have an '88 wiring diagram & I think all fuel & ignition wiring may be the same for '87 & 88, only the body was changed. My diagram shows all fuel & ignition wiring going to or through the ECU at one time or another. I would check the wires going to the ECU to see if they are burned, & even if you do not see burned wires I would take the ecu out & take the cover off & look inside for burned circuit board or electronics. These would certainly make the smoke that you saw.
    Also on my '88 there are 3 relays in the engine compartment on the firewall in front of the passenger side. They are under a black plastic cover. One is the ignition relay, one is fuel pump relay. I don't think yours were burned as the smoke probably would not have come into the cab, but you can use these to diagnose which wires are burned by finding out if the ignition relay is being held closed, by burned/shorted wireing or burned shorted ECU. If the relay is not opening & closing as you turn the ignition switch on & off then it is being held closed by burned wire or ECU. You can verify this by starting engine, then shut off ignition switch & when engine stays running, disconnect relay & it should stop. If so, then trace wires of proper color according to your wiring diagram & relay, back to inside & you should be able to trace them to source of short/burned area. Since you have not been able to see any burned wires anywhere under the dash I believe you will find something is burned inside ECU, or at wires right where they go into ECU plug connector.
  10. Bigbomber

    Bigbomber New Member 1000 Posts 100 Posts

    Welcome to the site!

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