Mk2 2 1.8 8v PB misfire/judder randomly when driving

Discussion in '8-valve' started by Mk2daz, Jun 5, 2017.

  1. Mk2daz

    Mk2daz Paid Member Paid Member

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    Hi all iv got a 1991 mk2 8v gti and its recently been developing a very strange misfire type judder when driving in gear.

    It used to do this a while back and when it did it would completely cut out eventually, then start back up fine. SO i changed the ignition switch and the coil and cleaned up all my ground terminals and it has been fine for the pas couple months.

    Now the past couple days it has returned however this time the car does not cut out it just judders for a split second at completely random times.

    To best describe it its as thoiugh someone has cut off the power to the car for a split second and so it feels like it has misfired. Im not convinced its timing related though as the car can run sweet for hours then this will happen randomly and the timing has been set and most of the spark related components have been changed (coil, dizzy, leads, plugs, TCI unit etc)

    There has been a fair bit of rain lately so i was initially thinking there was water getting into the fusebox causing some intermittent behaviour, dropped the fusebox today and the carpets and everything in the fusebox area is bone dry, took out the scuttle and cleared any debris, dried it up and made sure sunroof drains were cleared also. CHecked each relay and fuse for water damage but nothing that i can see.

    Its almost as if the fuel supply has been cut for a split second or iv lost a spark for a split second or as i mentioned the power has been cut for a split second.

    The car can run forever at idle but when its under some kind of load it seems to happen randomly

    DOing my head in as use this car everyday and the fact its intermittent is very frustrating! :thumbd:

    Can anyone shed any light on the situation?

    Heres the car in question :

    [​IMG]

    cheers, daz
     
  2. Tristan

    Tristan Paid Member Paid Member

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    Pull the plug off the MAF, pull the rubber boot off and check for broken wires. Also for corrosion on the pins on the MAF. I spent weeks chasing a very similar issue on a 90 1.8 digi.

    Also your vac lines, including the one to one MFA.

    And another less obvious one, the fuel pump wiring underneath.
     
  3. Mk2daz

    Mk2daz Paid Member Paid Member

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    Hi mate cheers for the info

    Took a look at the plug just now and pulled back the rubber boot the wires are all in tact and the terminals are clean and free of corrosion, the plastic in the plug was a little bit damp/greasy but nothing that would cause a connection issue i dont think, dried it up anyway.

    I need to throughly check my vac lines i replaced a few last summer but never really checked them properly, particularly around the inlet manifold, what is the bestv way to check for leaks, run the engine and spray carb cleaner and check for idle change? it idles pretty well just now but not sure if that means theres no leaks..

    And il get underneath it when i next get a chance to inspect wiring, due a fuel filter anyway so i can look at it then

    thanks again il hopefully get to the bottom of this
     
  4. Mk2daz

    Mk2daz Paid Member Paid Member

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    Little update on the scenario:

    Drove the car yesterday and again today as needed it for work, it juddered again on the way home and both on the way in and way home today. This time i managed to floor the clutch so it was crusing at idle when it hapopened again, basically the revs just blipped for the split second, no dash lights and there was some clicking from the fusebox, as if it was the relay going nuts.

    The fuel pump relay is a 167 one and it was brand new fitted about a year ago. Im going to put on a new fuel filter, add some redex to clean up the injectors, check the pump wiring, maybe try a new relay, try source a good working fusebox and ensure all my vac lines are good

    I think the CO should be okay as its been around 1% and below the past 3 MOTs, the ignition switch is aftermarket and was new 2 months ago but surely it wont be going already?

    Getting quite frustrating trying to diagnose this:thumbd:
     
  5. Tristan

    Tristan Paid Member Paid Member

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    sounds elecreical, you could bypass the fuel pump relay with a direct loop for test purposes?

    Gorgeous looking car btw.
     
  6. Mk2daz

    Mk2daz Paid Member Paid Member

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    Thanks very much.

    And that's what I was thinking but I'm
    Not keen on driving it with the pump continuously running, although for all a new relay costs I think il just replace it to rule that out, cheers!


    Sent from my iPhone using Tapatalk
     
  7. Toyotec

    Toyotec CGTI Committee - Happy helper at large Admin

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    if the intake boot has a split the above topic headline will occur. I have this before on an 8v digifant.
    Having done 1000s of miles in 8v MK2 cars, I can say digifants are pretty reliable things. They either work or do not!
     
  8. Mk2daz

    Mk2daz Paid Member Paid Member

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    Went out to start the car today, the left headlight was on! keys were out the ign, headlight switch was off, rear light was off, it wasnt parking light either as indicators were off!

    When i went to start it i got lots and lots of clicking from the fusebox, video in the link below

    I think i can quite confidently say its electrical, im about to give the fusebox a thorough inspection and i also have a spare one to swap over

    https://www.youtube.com/watch?v=nMagebXpytc

    daz
     
  9. Mk2daz

    Mk2daz Paid Member Paid Member

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    found some water seeping in ever so slightly from the corner of the windscreen so dried it up and seal the windscreen with some vaseline for now, then i swapped over to my old fusebox (cant remeber if it was working 100% either) and il see how it goes next couple days, in the meantime im gonna get my hands on a good working fusebox, hopefully it'll be alright
     
  10. Mk2daz

    Mk2daz Paid Member Paid Member

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    well the other fusebox didn't last very long as I experienced the same clicking and juddering just there, hmmmm....


    Sent from my iPhone using Tapatalk
     
  11. Mk2daz

    Mk2daz Paid Member Paid Member

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    Put on new fuel filter yesterday and checked the pump wiring, its all good and in tact (behind the rubber boot too)

    Tested all my relays this morning with my multimeter and 12v supply individually to confirm if they are good or not

    first checked the resistance across the input pins that energise the coil in the relay, then i connected a 12v supply to the pins to check the relay clicked, then i made sure there was near enough zero ohms across the output pins when power was supplied to the other pins

    Providing iv done this right then all the relays came back good and i expect they should be as they were brand new vw items less than 12 months ago

    I have another fusebox hopefully arriving tommorow that is apparently corrosion and water damage free so il swap that in.

    If i experience the same issue again then what can it possibly be!?
     
  12. Tristan

    Tristan Paid Member Paid Member

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    Corrosion on the pins in the plugs on the fusebox, or on the earths behind the fusebox.
     
  13. Mk2daz

    Mk2daz Paid Member Paid Member

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    Got another fusebox arriving today hopefully,

    and by the earths behind the fusebox do you refer to this earth bridge in the picture? mine was sitting loose and only had 3 wires earthing to it so i clipped it back on to the peddle box, not sure if this will have any difference or not

    [​IMG]

    cheers
     
  14. Tristan

    Tristan Paid Member Paid Member

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    Corrosion in the plugs of the loom, where they clip onto the fusebox.

    Yes, that earth "tree".
     
  15. rubjonny

    rubjonny Administrator Staff Member Admin

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    that tree should have 1 wire from F/4 to supply the earth, though its unlikely to casue your issue as its only an earth for extra bits n bobs that are unrelated to engine management. the important earths are all direct to the fusebox or to engine/battery
     
  16. Gareth Whyley New Member

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    Hi Daz, did you ever get to the bottom of this? I'm currently experiencing the exact same issue and it's driving me insane. Wondering if you got it sorted and can remember what it was that solved it for you.
     

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