Car intermitantly jerks at constant speed

Discussion in '8-valve' started by SiddyGTI, Jul 3, 2019.

  1. SiddyGTI New Member

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    Hello,

    I've got a 91 GTI 8v Digi, and today cruising at 70 on the motorway the car jerked forward and then went back to normal straight away. This happened twice with about a 30 second gap between, and then once or twice just before turning off later on. Not sure if this is a misfire, but I could replicate the sensation by bliping the throttle and lifting straight back off. Does anyone have any ideas where and what I should start checking to sort this?

    Thanks in advance
     
  2. costel1969 Paid Member Paid Member

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    I would start with the basics - confirm fuel filter and fuel pumps (wiring/condition) are OK. Presuming they are give confirm rotor, distributor cap, HT leads, coil and spark plugs and blue sensor (see RJ's guide) are all good. After that it's https://clubgti.com/forums/index.ph...ose-and-tune-your-mk2-digifant-gti-8v.124949/ as kindly provided by RJ.
    If that doesn't get her going like the clappers nothing will...
     
  3. H8V

    h8v New Member

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    After checking the above,

    1. If the rev counter drops down when this happens it might be the hall sensor in the distributor that is beginning to fail.

    2. Have someone blip the throttle to replicate the problem while you have a look at the engine to see which cables are flexed when the engine rocks. Look especially at the plug and two wires that operate the injectors.

    I've just suffered a problem where the engine would rev fine when stationary, but stopped whenever I tried to move off. One of the wires into the injector plug had fractured all its copper strands and was just hanging on by part of the plastic insulation. Any engine movement broke the connection, meaning no fuel injection and a stalled engine. Had me puzzled for an hour or two.
     
  4. pigbladder Forum Addict

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    hall sender isnt a bad shout ...often the rev counter goes mad with this

    other thoughts ecu relay , check battery terminals and earth cables are clean and tight
     
  5. rubjonny

    rubjonny Administrator Admin

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    have a close look at the clocks if it happens again, if it looks like they reset at the same time look at the ignition switch and wiring. Check the ecu and fuel relays for corrosion and water damage, wiggle to ensure seated. Slots 1 and 2 if CE1, 3 and 12 if CE2.

    Couple times I've had this, first it was CO set a little weak and 2nd time it was burnt out fuel pump fuse due to fusebox damage. fuse 5 is CE1, 18 if CE2 :)
     
  6. SiddyGTI New Member

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    Not had chance to properly check yet as I'm waiting for a new fan and in this weather dont want to risk over heating, but followed the set up guide and found the allen screw on the MAF took quite a few turns clockwise before a smooth idle was achieved so crossing my fingers this was the problem and it was running lean (I believe that is the correct way round?)

    Will confirm if this was the issue after more use and will work through the suggestions if not and update. Thanks.
     
  7. SiddyGTI New Member

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    Took her along some b roads and a bit round town last night with no issues, and have done the commute from Nottingham to Sheffield this morning without any jerking. Think running rich has been the problem, had to turn the allen screw on the MAF clockwise (think this is the correct way round and me saying lean in the previous post was incorrect). Thanks for the help.
     
  8. rubjonny

    rubjonny Administrator Admin

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    clockwise richens the mixture, anti-clockwise leans it :)
     

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