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Running unevenly

Discussion in 'Engine & Transmission' started by Basil Bus, Oct 14, 2018.

  1. Basil Bus

    Basil Bus New Member

    Messages:
    4
    Location:
    Hobart
    I'm having a problem with my 1976 2 Litre Bus and neither of the most respected Kombi mechanics in Hobart have been able to sort it:

    At about 40K in 3rd gear and 50 - 60K in top it runs very unevenly. The feeling is much as if it's missing, although it's not actually missing; there's no dramatic lack in power. Above and below those speeds it runs smoothly. Whether it's accelerating or decelerating doesn't make any difference. It seems to be much better when cold and becomes more noticeable as it warms up. For some reason the unevenness isn't apparent in 2nd. Whatever the cause it has steadily been getting worse over a couple of years.

    I've also been trying to sort some starting issues and in the course of my investigations found that the voltage difference across the two terminals of the coil is usually around 5 Volts. It seems to be quite variable, anywhere between 4.8 and 8 volts but mostly around 5. I've read in a couple of places that it should be at least 9.6V. I've mentioned it to a couple of auto electricians who don't seem to attach much importance to it being so low. Don't know if this is significant, but it's fitted with electronic ignition (not sure what brand, it was years ago).

    Any opinions would be welcome.
     
  2. oldman

    oldman Super Moderator Staff Member

    Messages:
    8,044
    Location:
    Avalon Beach NSW
    Hey Basil...welcome to KC ;)
    More noticeable when warm would indicate, to me based on my experience with similar issue, that you have an electrical resistance issue....
    Try swapping out the HT leads, including the lead from the coil to the dizzy.
    If that doesn’t help, swap the coil out.....they’re not that expensive.
    Also worth checking the carbon block in the dizzy cap itself....can sometimes have a hairline crack...
    Good luck, start simple and work up from there.
    Let us know how you go.....it’s how we all learn here:cool:
    Cheers,
    Mark
     
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  3. David H

    David H Well-Known Member

    Messages:
    3,563
    Location:
    newcastle
    Vacuum canister territory;).
    Cheers
     
  4. Mordred

    Mordred Super Moderator Staff Member

    Messages:
    2,706
    Location:
    Penna, Hobart
    Do you have a standard dizzy you can swap out and try. An electronic dizzy is fine but sometimes when you are trouble shooting it pays to go back to the basics and original set up. No guarantees but might be worth a try.

    I am out near Sorell and should have some bits you can try. PM if your are interested.

    Adrian
     
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  5. Dapom

    Dapom Well-Known Member

    Messages:
    638
    Location:
    Brisbane
    Hey :) I had a very similar issue with my bus. It had an accuspark or other unstamped generic Chinese electronic ignition in it with matching coil. It all bench tested perfectly and so I always thought it was all good. I changed pretty much everything else...HT leads etc etc and still had the issue. Finally I changed out the electronic ignition module to a pertronix ignition 2 and matching coil and have had no issues since. I then ceremoniously burnt the accuspark module :) I wouldn’t advise playing parts darts but if you’ve swapped out plugs, HT leads, dizzy cap and rotor and the issue is still there then that’s where I’d be heading :)
    Only other thought is rust in the tank. Slight fuel starvation can make it feel like it’s missing. Maybe change out the fuel filter and open the old one up to see what’s in there. Good luck! I know from experience how annoying intermittent problems can be to diagnose and solve ;)
     
    oldman likes this.
  6. Basil Bus

    Basil Bus New Member

    Messages:
    4
    Location:
    Hobart

    Hi Adrian,

    Thanks for the offer. It would be great if I could find a spare dizzy I could try. That would help narrow it down. At the moment I'm not sure if it's fuel or ignition.

    Mark
     
  7. Mordred

    Mordred Super Moderator Staff Member

    Messages:
    2,706
    Location:
    Penna, Hobart
    Not sure what my movements over the next couple of week are but we should be able to sort something, even an evening possibly now that we are in daylight savings.

    Adrian
     
    Grantus likes this.
  8. Basil Bus

    Basil Bus New Member

    Messages:
    4
    Location:
    Hobart
    Cool. I'm very flexible. An evening would suit.

    I have found something that could be significant. A little while ago I replaced the plugs and thought one looked a bit different. I inspected the new ones yesterday and one was noticeably blacker than the other three. That was after just 600km. Doesn't really look oily to me but I'm no expert. The insulator was yellower than the others.

    Any idea what this might mean?

    Mark
     
  9. Mordred

    Mordred Super Moderator Staff Member

    Messages:
    2,706
    Location:
    Penna, Hobart
    Going out on a limb because there is a lot of variables that can cause it, but I am suggesting it might be the distributor cap contact or the lead to that cylinder not transmitting the spark well to that plug. Not firing with enough voltage can cause it not to clean burn or achieve the right temperature, but it could also be the cylinder is not sealing as well and the compression may be lower, but it is unusual. You would need to do a compression test on all the cylinders to confirm that they are all similar. Easier to maybe change out the lead and see if it makes a difference to the plug and the funny running. Also check the dizzy cap and see if that has any cracks or burns on that cylinders connection.


    Adrian
     
  10. Basil Bus

    Basil Bus New Member

    Messages:
    4
    Location:
    Hobart
    I can't claim to be a mechanic but I was wondering if it could be an ignition issue. I checked conductivity of the lead and it seemed on a par with all the others. Had a look inside the cap to see if the terminal for cylinder 4 looked OK. It looked pretty much like all the rest. I'll see if I can get someone to do a compression test for me.

    Many thanks for your help so far.

    Cheers,

    Mark
     
  11. cbus

    cbus Well-Known Member

    Messages:
    10,927
    Location:
    sunshine coast
    Agree with all that Adrian posted.

    Re plug
    Testing a wire cored lead won't show much unless there is a full failure.
    If you are running carbon leads then its worth replacing with original wire cored.

    Try pulling the offending lead and put a good plug in it then earth the plug body . run engine and observe.

    Also check at night for stray sparking on leads and contacts.

    Possible that spark plug cap is faulty. Common.
    Swapping with a known good unit easiest check.

    Fluffy black on plug is unburnt fuel. Missfire being a likely cause if other plug on same side is good so its worth chasing.
     
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  12. Mordred

    Mordred Super Moderator Staff Member

    Messages:
    2,706
    Location:
    Penna, Hobart
    If you get stuck I can borrow a compression tester that is easy to use and screws into the spark plug hole than the push and hold one that I have. Either will do but the screw one is easier for bus engines.

    I have found a complete dizzy that will do(needs some shims but good enough for a test) and good vac can, with cap and leads except the centre one, but that should be enough to prove other components.

    Adrian
     
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