Truck won't start after sitting for years

Discussion in 'Tech Discussion' started by agreiner, Jul 8, 2018.

  1. agreiner

    agreiner Junior Member

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    As promised in the intro thread, I have returned with photos, and some test results.

    First, the project: a beaten and battered 87 V20, which has seen severe neglect. My objective at this point is to make it move under it's own power, since I have nothing capable of moving it, to a slightly more suitable work area.

    My issue is that it cranks, but won't fire. I was hoping to make it move before I have to drop the tank, but that may not be happening. My current theory is that old fuel has gummed up the works somewhere.

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  2. agreiner

    agreiner Junior Member

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    Here are some photos of the Throttle Body, and the wiring of the ignition system. The only visible issue is some stripped insulation on the hot wire into the right (passenger side) injector.

    Here is what I was able to determine with the trusty multimeter, with the key in the "on" position:
    Injector (Right side): Black (Blue or green?): 12 V, white: 0 V.
    Injector (Left Side): Black (Blue or green?): 12 V, white: 0 V.

    The coil has two plugs in the top: Gray and Black.
    Gray plug: Pink: 12 V.
    White: Not connected to anything (tach?)

    Black plug: Pink: 0 V, but no continuity to ground.
    White: 0 V, but no continuity to ground.

    TPS:
    White: 5 V
    Blue: 0.03 V (not 0, but not much either)
    Black: 0.03 V (same)

    Do these readings appear correct?

    I was unable to remove the distributor cap today, because the only extension I had with me was 6", just enough to hit the firewall and keep me from getting a wrench on it.

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  3. 1987 GMC Jimmy

    1987 GMC Jimmy Full Access Member

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    Okay, so first off, the two plugs at the back of your distributor are plugged in? I thought you said before one wasn’t, but I may have misunderstood. The first thing I’d do is ditch that injector connector with the bare wire. The best way to proceed is to get a new connector, cut the old one off, slip some heat shrink over the harness portion of the wire, unsheath a portion of the harness wire, twist the two sets of new and old together, solder, and slip the heat shrink over and warm it up. There are other ways to perform harness repairs (i.e. crimp connectors), but that one will have the cleanest, most sightly result.

    The consistency on the injectors bodes well for their function, but I like the noid light method of testing for pulse while you crank the engine and just watch the light out the windshield. It sounds like you’re getting your 12V to the ignition system, which is good. There’s a tach wire there, and the other two go to the ICM.

    You’re getting your TPS 5V reference, which is good. The black wire should be tested (key on) with the red probe at the battery positive terminal and the black probe on the black wire. 12V verifies good ground coming to the sensor. The blue wire should probed with the connector plugged in and read .5-.6V with the key on. It should be that at idle, and as you move the throttle towards WOT, the reading should smoothly ascend to 5V. If it doesn’t do so smoothly, the sensor’s no good.

    The cap is held on by two Phillips screws. You undo them, and it pops right off. The bolt down in that crevice is the distributor hold down. That’s for your timing adjustment or removing the whole distributor so I wouldn’t mess with that yet.

    Have you been able to verify spark? I had to do this a few days ago, and I just used a test light probe and hovered it over the coil to verify it was good and then hovered it over one of the eights distributor cap pins to make sure spark was leaving there as good as it arrived. Also, are you hearing your fuel pump when you turn the key on.
     
  4. agreiner

    agreiner Junior Member

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    Fuel pump does run when the key is turned on.

    The distributor cap *is* held on with Phillips screws, but they are also 5.5 mm hex head, which is what I was using the wrench for.

    Sent from my Moto E (4) using Tapatalk
     
  5. 1987 GMC Jimmy

    1987 GMC Jimmy Full Access Member

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    Gotcha. It sounds like it’s close to doing something to me.
     
  6. chengny

    chengny Full Access Member

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    A good initial diagnostic is to get a can of ether (starting fluid). Shoot a good blast directly into the throttle body. Then - quickly before it has time to evaporate - crank the engine over. If the engine fires up (it will probably only run for a few seconds), that would seem to indicate a fuel supply issue. If there is no change (i.e. the engine cranks but still doesn't fire)...you should concentrate on the ignition system.

    That test may not tell you exactly what the problem is, but it will point you in the right direction.

    However, before anything else, verify the ECM is operational (confirmed by the SES light being illuminated with the ignition switch in RUN position). If there is no Service Engine Soon warning with the key on, you'll have to deal with that first (because you are not going to get anywhere until it is).
     
  7. 78c10bigten

    78c10bigten Full Access Member

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    Thats also assuming that the light hasnt burnt out or been previously removed.
     
  8. agreiner

    agreiner Junior Member

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    SES light is illuminated in the on position.

    Sent from my Moto E (4) using Tapatalk
     
  9. Jppr26

    Jppr26 Member

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    Clean the contacts on the distributor and check for spark, I would even give a few squirts of atf from a oil can into each cylinder to help build compression
     
  10. agreiner

    agreiner Junior Member

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    Finally got some free time to work on this beast...then it started raining. I was able to use a spark tester to check for spark...no go. Thus, I'm off to research the coil and how to test it. It's pretty well rusted, but I want to be sure it's dead before I start chucking parts at the problem. I disconnected the coil and brought it home. Should be able to get it cleaned up and tested without too many headaches.
     
  11. chengny

    chengny Full Access Member

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    Ignition system diagnostic procedure (with remote coil):

    1.jpg

    2.jpg

    3.jpg
     
  12. 1987 GMC Jimmy

    1987 GMC Jimmy Full Access Member

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    Could be that, the ICM, or pickup coil. I’ve done the multimeter test, but I’ve also hovered a test light probe over the coil pin while cranking. It sounds like you’ve removed it so you’ll have to do the latter. The ignition module is a pretty common failure point, I’d say more than the other two.
     
  13. T-ROD

    T-ROD Full Access Member

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    The very first thing I'd have done if no startup occurred after so long of sitting, (especially after about a year or more) would be to check the fuel from injectors, or even on a carb I like to disconnect the line to it to see if it's got fuel going to it, just slowly unscrew last few threads, (BTW not much pressure on TBI but enough to be careful with) and maybe replace filter, and the coil of coarse usually can be checked through secondary ohm check if primary is alright, then of coarse secondary side should tell, it's usually in the thousands but not quite the tens place like 7,000-9,000 ohms, it may be rusted but usually got enough metal to carry magnetic field to give some fire to start, b or the old way and sure fire way of pulling a plug wire, or the main plug wire and pulling to where you can see a spark on intake away from TB and maybe on a bracket. The injectors you can check if you had a way for someone to crank you could see the spray pattern, or you could at least check pulsing to it with multimeter I've messed with those and you can have one injector clogged or unplugged and it wouldn't even have enough to pop or sputter and fire a cylinder at startup depending on temperature, some of them are precisely accurate, but they are good, and then I'd definitely check those first off, its probably something simple for sure. Basically if you have Have 1.compression; 2.Fuel; 3.Fire; 4.Air; 5.Good Battery for Cranking, it shouldn't have much holding it up, in fact it's almost impossible unless there's a major issue like jumped timing or fouled plugs which I'm sure it wouldn't be too many, and maybe it's either not getting enough fuel or flooding too, but you would probably smell that instantly, those can stick pretty bad, and if it's warm it will flood it quick, and that's the page of thoughts I can think of, probably not much you didn't check but it may give a lead to it somehow.
     
  14. roundhouse

    roundhouse Full Access Member

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    I doubt the lack of spark is the coil


    More likely something in the dizzy
    I’d pop the cap and clean the brass contacts inside

    Make sure you are getting fuel
    Disconnect the line at the TBI and see if the pump is working
     
  15. Crispy

    Crispy Full Access Member

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    Just another random suggestion here to make sure bases are covered. I had a Jeep that would crank and didnt want to start after sitting for extended periods. It was always the battery ground to chassis cable, i would have to remove it and reinstall it. Double check your grounds for good contact and cables for corrosion. Just for peace of mind.
     

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