Mk2 1.3 manifold pre-heater weirdness?

Discussion in '8-valve' started by tapehead_01, Jan 17, 2018.

  1. tapehead_01 New Member

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    Right, so if I go to start my 89' golf 1.3 (with a Pierburg 2e3) when cold it'll fire right up fine, run smoothly for the first say 20 secs, then start to misfire. Revving up to about 3k rpm will clear the misfire after about another 20 secs but I doubt this is good for the engine, especially when cold. Misfiring is typically worse the colder and more humid the weather is. However I've found that if I sit with the key in the accessory position for at least 2 mins+ the manifold pre-heater will warm the carb and it'll start fine and not misfire at all. Thing is over 2 mins seems to me like quite a long time for the pre-heater to warm up, is this normal or should it be warming far quicker than this?

    The other problem I've faced is that once warm, if I park somewhere for anywhere over about 30 mins the car won't start unless I hold the accelerator pedal to the floor. Anywhere under 30 mins and it'll start but idle a bit low before picking up after a few secs. I'm not sure if this is vapour lock or something, but I did make sure to route the new fuel lines in the same places as the factory ones were. The overrun fan works fine as well (though only really switches on when the weather warms up).

    Things done to the car include:

    > Rebuilt and cleaned out Pierburg 2e3 carburettor, new flange, gaskets, accelerator pump, vacuum lines etc...
    > New, good quality fuel pump
    > New fuel lines, fuel filter
    > New head gasket, oil stem seals, inlet manifold gasket
    > New distributor (couldn't just buy vacuum advance unit separately)
    > New coil, HT leads, plugs
    > Flushed coolant system, new radiator, thermostat & housing

    Admittedly I adjusted the carb myself so no idea how accurately I've done it since I don't have the equipment (I didn't adjust the choke mechanism though, just left it as it was), though the exhaust gas results from a recent MOT put the CO level at 1.96% which I think is about right, and it runs really nicely after it's stopped misfiring! I think the mixture screw is about 1.5 turns out.

    So, any ideas what I might have missed that may cause warm-start issues or if the pre-heater is working correctly?

    Thanks
     
  2. EZ_Pete

    EZ_Pete Forum Junkie

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    The hedgehog can degrade over time, as I found out with my 1.6 driver. I measured the resistance between the feed-wire and ground and got a much larger number than expected (should be well under 1 Ohm, from memory). I dissected the old one when I finally got round to replacing it, and found it to be quite simple. Four little PTC heater discs, with a sprung contact mechanism that leans on them. I think the blackness of the contact areas is the problem, oxidation of the silvering on the surface, giving higher contact resistance which limits the current. Couple of pics here: https://www.dropbox.com/s/8im1vgyzby71jdc/PTCs in hedgehog.JPG?dl=0 and here: https://www.dropbox.com/s/sio9fi4nsu58462/Hedgehog contacts.JPG?dl=0.

    I might just have a new spare somewhere in the shed, acquired in the days when I used to collect Pierburg-related bargains off Ebay.

    Measure the resistance of yours (with cold engine) and see what you get.

    Another thing to look at, possibly, is the part-throttle enrichment valve on the side of the carb. If the diaphragm inside there breaks/leaks it can drip fuel down into the manifold via its vacuum feed, and make hot-start very difficult. Can't remember quite how easy it is to remove/inspect; maybe just two screws?
     
    tapehead_01 likes this.
  3. Tristan

    Tristan Paid Member Paid Member

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    Could you use a couple of diesel heater plugs for similar effect?
     
  4. tapehead_01 New Member

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    Thanks for the info and the photos, unfortunately I don't have my multimeter with me at the moment since I'm at uni and forgot to bring it with me... I suppose a cheap one would at least give me a rough idea if the pre-heater was working or not, might go and buy one tomorrow. After 2 mins I can still put my hand under the manifold, touch the base of the pre-heater and it feels luke warm, but I don't know if that means anything seeing as it's heating the fins, not the base. If you do happen to find your spare (and are willing to part with it of course), and it turns out mine is broken I'd be very happy to buy it off you.

    As for the part-throttle enrichment valve, I replaced all the gaskets and rubbers in it when I fitted the new gasket set to the carb. I assume if it was still leaking it'd be an internal leak so not one I'd be able to see from the outside of the carb?
     
  5. EZ_Pete

    EZ_Pete Forum Junkie

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    Sounds like you've ruled out my theory about the power valve, I'll have another think about the starting symptoms tomorrow, I'm not sure I can remember enough about these carbs, but I'll have a go.

    Have you tested the pulldown unit? I remember those being a common failure.

    If you do find that your hedgehog is reading higher resistance than it should, just PM me a good delivery address and I'll post out my spare. I'm pretty sure I can find it, I moved into a new workshop/shed recently so I've seen it within the last month. I have no use for it, but don't want to throw it out, so I'd be happy to donate it to you. :)

    Edit: Full disclosure; first attempt to find the spiky little fella just now was a complete failure.
    Don't give up hope though. I just need to look for something else and it'll probably turn up. Not as confident as I was earlier though...
     
    Last edited: Jan 17, 2018
  6. tapehead_01 New Member

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    Hmm yes tested all the vacuum stuff, all seems to work fine. Pulldown unit and auto-choke stuff, TTV, all that works, even does the cold start procedure properly (holds revs at 2k for 5 secs then slowly drops down to idle). I was pretty happy that I got that to work, just a shame it wasn't the end of the problems :p

    Thank you so much! It's not urgent or anything, I'll go and buy a multimeter tomorrow, leave the car to sit over night to cool down completely so should know if the hedgehog's working some time friday. If you don't find it don't worry, let me know and I'll just rake through ebay until I find another used one (though I guess there's no guarantee a replacement of another car would be much better than the one I have already), unless of course it's possible to repair the one I've got?
     
  7. rubjonny

    rubjonny Administrator Staff Member Admin

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    have you checked over the warm air feed system, make sure the flap moves when the engine is started and the hose+shroud is all intact. fact its worse when cold/humid suggests to me its not quite working as it should
     
  8. tapehead_01 New Member

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    Alright checked the flap and seems to be working fine, moves to the up position directing air from the exhaust manifold shroud when cold-started. A while ago I did take apart and clean the orange switch thing inside the airbox so that should be working fine too. The tubing from the shroud to the airbox does have a small rip in it but it's been taped over so I doubt a significant amount of hot air is being lost through that.
     
    Last edited: Jan 18, 2018
  9. tapehead_01 New Member

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    UPDATE: Checked the resistance of the hedgehog this morning, registered between 1.5 and 1.7 ohms so I guess it's slightly out of spec. Connector was a little bit corroded so I cleaned that up but hasn't really made any difference.
     

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