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Please help backfire running rough mystery

Discussion in 'Bay Tech Clinic' started by jimmybay, Feb 25, 2012.

  1. jimmybay

    jimmybay New Member

    Messages:
    267
    Location:
    roxby downs sa
    Hello I've got a 1800 75 kombi.
    Last week she started to backfire and idle shit for about 5 mins then would come good. The periods of the backfiring slowly increased. At the moment we are traveling oz with my partner and 14 month old son Harper and I have found some work in stawell park NSW so it is important that the bus is running. we can't get in to a vw mechanic until next Friday so I am attempting to fix her myself.


    It is running a crowcam fireball xr700 elec ignition run through a gt40r coil and a ballast resister. Doss anyone have experience with this set up????

    What I have checked so far:
    Fuel flow rate is good
    Leads are good
    No vacume leaks I can find
    Changed out coil
    Checked connections

    Had a service on Tuesday but was running fine both when I took it in and when I drove home.the prob was occurring before the service.

    I would appreciate any help as I can't afford to loose this job over transport.
     
  2. splitbus

    splitbus Well-Known Member

    Messages:
    3,281
    Location:
    Brisbane
    Check the rubber elbows on the balance tube, under each carby on the manifold, are you using e10 fuel, also replace fuel filter, just some quick thoughts

    Also it could be water in your fuel, I had a problem just like that back in the 80's on my 72 camper, had it serviced, ran great for a while, then it started the same problem again
     
    Last edited: Feb 25, 2012
  3. cbus

    cbus Well-Known Member

    Messages:
    10,921
    Location:
    sunshine coast
    Couple of long shots.
    does the engine run hot when prob occurs. does coil seem over hot?

    dont know resistance requirements for the ign but May??? be a source of prob. Was it ok previously with this setup?

    Had an issue with crap in fuel tank causing intermittent blockages which made engine run hot/lack power/generaly fart around. hard to track.

    check a plug for signs of lean/hot running.

    does it run ok cold?

    using 95 fuel?

    col
     
  4. oldman

    oldman Super Moderator Staff Member

    Messages:
    8,043
    Location:
    Avalon Beach NSW
    As Col & Mike suggest, check the fuel filter -was it replaced in the service?
    Could also be water in the carb. float bowl from a dodgy fill too.

    I can't quite follow your quote above....?

    Hope you get it sorted. Cheers, Mark
     
  5. jimmybay

    jimmybay New Member

    Messages:
    267
    Location:
    roxby downs sa
    I dropped the fuel out yesterday to replace the fuel lines and filter. I'm not running e10 I have sprayed the elbows with wd40 with no change to idle I might take them off to check. The fuel flow was ok so a blockage seems unlikely.She has run perfect with the ignition setup for the last two years. I tried to get a new ballast resister this morning but had none in stock. The coil dose not seem too hot I'm thinking of replacing dizzy , coil and ignition with a more commen setup.(brand)
     
    Last edited: Feb 25, 2012
  6. jimmybay

    jimmybay New Member

    Messages:
    267
    Location:
    roxby downs sa
    Sorry mate it was happening a few days before the service.
    I was just eliminating anything done buy the service mechanic. Ended up sounding like a riddle whoops :umm:
     
  7. oldman

    oldman Super Moderator Staff Member

    Messages:
    8,043
    Location:
    Avalon Beach NSW
    No probs. just trying to work through possibilities, that's all. Helps to have a clear picture/timeline.
    When it was serviced, they didn't alter the timing did they?
    Once you have EI installed & timed to suit, there should be no need to touch the dizzy/timing ever again....
    Cheers, Mark
     
  8. oldman

    oldman Super Moderator Staff Member

    Messages:
    8,043
    Location:
    Avalon Beach NSW
    Check the dizzy locking plate/bolt. If it's worked loose there's a chance that the dizzy has started to rotate through vibration - that'll cause havoc with your timing.
     
  9. Kai

    Kai Well-Known Member

    Messages:
    4,683
    Location:
    Eastlakes, NSW
    Intermittant problem sounds electrical.

    Are the cables on the idle cut of valves, would cause poor idle.
    Spark Plugs
    Leads
    Can you take it back to points and condenser?
     
  10. oldman

    oldman Super Moderator Staff Member

    Messages:
    8,043
    Location:
    Avalon Beach NSW
    ...as Kai suggests - could be your EI module is on the way out .....? How long ago was it put in ?
    If everything else is ok, that's a likely bet.
     
  11. jimmybay

    jimmybay New Member

    Messages:
    267
    Location:
    roxby downs sa
    I think your right about the EI being stuffed I've checked just about everything else. I am 90% sure it's electrical I'll have to wait till next Friday might be able to catch the train from Coledale to stanwell park. Thanks for trying to weed this problem out lads I'll get it swapped out Friday see how that goes. Thanks again
     
  12. oldman

    oldman Super Moderator Staff Member

    Messages:
    8,043
    Location:
    Avalon Beach NSW
    Plenty of posts on this elsewhere, however most EI modules fail 'cause they're cheap-ish versions of reputable brands or they've been installed by the owner - "How hard can it be....."
    I know a couple of fellas that build high performance VW engines for a living & swear by EI modules. Both reckon it's usually installer error or cheap module choice that results in failure. Cheers, Mark
     
  13. nikferatu

    nikferatu Active Member

    Messages:
    1,457
    Location:
    Bracken Ridge, Brisbane
    Had a similar problem with backfire on overrun, after removing the screw in solenoids and ensuring the passages were clean the problem went away, particularly the larger one in the right hand carby. Mine had a small amount of debris in the little drill holes in the end of the solenoid which was enough to cause the problem. Could be a long shot but worth checking before buying too many new parts.
     
  14. jimmybay

    jimmybay New Member

    Messages:
    267
    Location:
    roxby downs sa
    I did disconnect the idle solenoids briefly and they have power didn't remove them to check for grit will tonight along with the locking plate. I think the cranecam sells for around 140 pretty cheap. it was already on the bus and was running fine so I had no need to change it out. I don't think many EIs could handle the heat of a Vw engine bay so it may have failed because of heat. The mechanic will change it over with a test set he has. I would try myself but 99% of my spare parts are in SA.No use buying 200 bucks on parts if they don't fix the prob
     
  15. Red Kev

    Red Kev Member

    Messages:
    468
    Location:
    Moonee Beach
    Don't know the specifics of your coil/EI setup, but I'd be question the coil. Other EI modules hate ballast resistors, and need 3 ohms. EDIT: that's assuming the ballast resistor in internal to the coil. If it's external, than total resistance (coil plus resistor) should be 3 ohms.
     
    Last edited: Feb 26, 2012
  16. cbus

    cbus Well-Known Member

    Messages:
    10,921
    Location:
    sunshine coast
    going over old ground , but.
    when you dropped fuel you checked filter gauze in tank outlet if you have the nut type of outflow connection that unscrews from tank?

    like the swap whole disy/coil to check proceedure.

    does the idle cut off valve screw in securely.


    if all of above ok then maybe a double check of valve adjustment and that adjusters are not dodgy?

    cold run ok? change when hot?

    change cap and rotor. have had a cap with tracks through it misfire. hard to see.

    col
     
  17. ttmck

    ttmck Super Moderator Staff Member

    Messages:
    2,733
    Location:
    Hallett Cove STH AUS
    Is the back fire like a gun going off = electrical
    Is it a poping sound on decleration or hesitation hic cup on acceleration = fuel

    Your answers are in above posts but you need to identify exactly when its happening other wise this will keep going round and round
     
  18. jimmybay

    jimmybay New Member

    Messages:
    267
    Location:
    roxby downs sa
    Ok the bus is now running sweet :)
    The reason for the backfiring is still a mystery.
    We replaced the coil lead put two new idle jets in swappedover the dizzy coil and EI with no change. Until it was taken out and given a flogging and with one last KABOOOM followed by black smoke she burst into life.
    The problem must have been fixed but had fouled the plugs so the engine still ran crook until it was driven hard :/
    So we will never know exactly what the cause was .
    Thanks everyone for the help and advise
    I have pulled apart and tested a few things I had not been game to touch inthe past.
    Now the kombi is running well we can Continue travel thanks again :)
     
  19. Grantus

    Grantus Well-Known Member

    Messages:
    14,738
    Location:
    Southern ACT
    I love a happy ending...:)
     
  20. jimmybay

    jimmybay New Member

    Messages:
    267
    Location:
    roxby downs sa
    Ok problem is back :/
    Engine was idling high after the problem was fixed.
    Changed out sparkplugs idle dropped right down and now it's dying under load
    Carbs may be on the way out.
    Or burning out leads and coil? What would cause this?
    I'm bloody close to traveling home and putting the 2l in that I have but that means stopping our trip and working for a few more months.
    Can't get into a mechanic till Tuesday. Hopefully he can solve this prob!!!
     

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