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Starting problems.

Discussion in 'Chevy Trucks' started by DMK86, Jan 21, 2007.

  1. DMK86

    DMK86 Junior Member
    from Canada
    Messages: 5

    I recently bought an 86 GMC half ton. I swapped out the 305 for a 350. When i got the truck it wasn't running, the 350 i put in had no issues starting or running. When i go to start it now the starter engages slow and extremely rough. I ran a switched wire to the s terminal on the starter and it turns over fine with the ignition switched off. I have also put in a new ignition switch and still the same thing.

    Has anyone had this problem before or have any suggestions?
     
  2. Sydenstricker Landscaping

    Sydenstricker Landscaping PlowSite Veteran
    Messages: 3,882

    How good are the ground connections to the body or frame? Those could cause some issue
     
  3. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    You didn't say whether this truck is a stick or an auto trans but when the crank wire (purple/white) leaves the ignition switch it either goes through a neutral safety switch (auto) or a clutch start switch (manual) before heading out to the starter. If the connection's are worn or corroded in either you'll experience the problem your having. You can make up a heavy jumper wire (10 gage min.) and jump the switch,whichever one it has, and try cranking it again.If it crank's good with the switch jumped them replace the switch.
     
  4. DMK86

    DMK86 Junior Member
    from Canada
    Messages: 5

    Sorry, i forgot to mention that. It is a TH350 auto. I have the neutral safety switch bypassed at the moment.
     
    Last edited: Jan 22, 2007
  5. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Take your jumper wire that you used to hot wire the starter directly off the battery and run it in the truck and touch it to the purple wire at the neutral switch and see how it crank's.This will eliminate the ignition switch and it's connection's from you diagnosis.Also make sure your fusible links in the wiring harness at the starter and on the junction block at the fire wall are in good shape.If one of these is in poor condition there may not be enough power feeding the cab and ignition switch. A GM starter solenoid require's nearly 40amps to pull the plunger in to engage the starter.If the ignition switch can't get the 40amps it needs to send to the starter the solenoid wont engage properly.
     
  6. DMK86

    DMK86 Junior Member
    from Canada
    Messages: 5

    I haven't been able to find any fusible links near the junction box but it seems like the engine wants to kick back when its about to fire.
     
  7. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Hmm,thier should be at least two at the junction block on the firewall and two at the starter.Did you check the purple wire to see if it has any power in it at the nuetral switch where you have it jumped?
     
  8. DMK86

    DMK86 Junior Member
    from Canada
    Messages: 5

    Yes, it cranked fine but as soon as i run power to the ignition switch it starts going all goofy. I have power at both power wires at the ignition switch and i put a new switch in and its still doing the same thing. It almost seems like its trying to fire up backwards but the starter is turning the engine over the right way and the engine timing is good.
     
  9. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    I know you said the timing is good but are you ABSOLUTELY POSITIVE? Its very easy to time them 180 degree's out.What about the firing order? Did you check that? Did you check the pink ignition wire at the distributor to see if it had power in the crank and run position's? Are you sure you connected the pink wire into the correct port on the distributor? That's another easily over looked item that will make you pull your hair out.
     
  10. DMK86

    DMK86 Junior Member
    from Canada
    Messages: 5

    I'm sure the timing is good, it did fire up a few times. I double checked the firing order and thats good too. I'm starting to run out of hair to pull out, i've never seen this kind of problem on a GM vehicle before.
     
  11. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Try running a jumper wire from the battery directly to the distributor and see how it run's. This will eliminate all your wiring and ignition switch as a problem.If it doesn't help any then you still have a problem with the motor (timing or fuel problem),it's not in the wiring.Note though, if it start's and run's it wont shut off until you disconnect your jumper.
     
  12. diehrd

    diehrd Senior Member
    from NY
    Messages: 199

    Try to crank the truck WITH the coil disconnected....
     
  13. And then if it turns over fine with the coil disconnected, you've definitely got a timing or firing order problem. What you are describing really sounds like the classic GM advanced timing issue meaning the piston is coming up against a closed intake valve and the spark plug fires an instant before reaching top dead center and "locks" the motor for an instant. If it's not that, then you might have the firing order swapped on 2 cylinders. It will give you the same symptom. Last but not least as stated earlier, you could have missed the distributor install by one tooth.
    As a long shot, check the inside of the distributor cap for carbon tracking between the terminals for each cylinder. I haven't seen that for years but you never know.