misfires and Hc too high

Discussion in '8-valve' started by Richard Gilberd, Nov 12, 2022.

  1. Richard Gilberd Forum Member

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    Hello all, well i've got my car so far (8v PF) that i am ready to go and get new papers for it, I had it on the tester and all was good managed to get the co to around 1 percent and all seemed to be running fine. on the day i drove it to the testing station without any trouble, but after they took it inside it started playing up and misfiring, co2 way too high ( they call it Hc i think which is basically unburnt fuel i geuss) so i took it home and put it back on the tester and i cannot work out what the problem is, this car has had everything new, i'll write a list;

    plugs, leads, cap, 2nd dizzy to prove the first isn't bad, new icv valve,blue sensor (pattern), new injectors, new FPR, 2nd maf as was suspect on the original, new knock sensor, new Earths all around, new lambda, new Catylasator, umpteen different ecu's!

    I am at a loss when i had the motor out i reground the valves in and new head gasket e.t.c , i think i'll do a compression test on it next although i just removed all the valves and they do look all equally sooty none wahed clean or anything, can running rich cause a misfire, our machine at work is brand new and maybe it has a problem!!(clutching at straws). if anyone can point me to what should look at next would be great.

    just as an extra thought would the knock sensor cause problems as when i unplug it it doesn't seem to make a difference.

    sorry for the long post.
     
    Last edited: Nov 12, 2022
  2. Tristan

    Tristan Paid Member Paid Member

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    Are you sure it wasn't HC, not CO
    ?
     
  3. Richard Gilberd Forum Member

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    yes you are correct Hc which is hydrocarbons maybe??
     
  4. GVK

    GVK Paid Member Paid Member

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    Have you got the result sheet to post ? Are you in UK
     
  5. Richard Gilberd Forum Member

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    not in the U.K (expat in Austria) the test results are as follows:

    idle Hc:130
    at 2500rpm Hc:160

    Lambda 1.05

    from what the guy told me at idle the Hc should be below 60 and the lambda should be under 1.03, gotta say this stuff is pretty foreign to me!
     
  6. GVK

    GVK Paid Member Paid Member

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    Stricter limits than a UK car of that age! I think our non-cat mk2s should be 3.0% CO and 1200ppm HC from memory ofdoing MOTs

    If its misfiring it will have higher HC naturally, so any air leaks or whatever can effect it. 1.05 lambda indicates a slightly lean mixture.

    Parts cannon well and truly fired at this one, no idea what to suggest really other than make sure the cat is nice and hot before test.
     
  7. Richard Gilberd Forum Member

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    lol, yes parts cannon true but this was bought as a non runner so pretty much everything has been changed!! everything that i thought i could save would let me down within a month!, still have no idea where this misfire is coming from, whilst driving it seems to be at around 2800rpm where it get's really bad but by wide open throttle it doesn't miss a beat
     
  8. GVK

    GVK Paid Member Paid Member

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    I see you've added an FPR, have you checked the fuel pressure? Wondered if it's not up to spec causing a lean misfire.

    Straws and clutching as they say lol
     
  9. Richard Gilberd Forum Member

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    no the Fpr was replaced but it was already misfiring before that, as i've done all the electrics i was on the route of thinking it must be fuel so new injectors anf FPR, runs alot better i must say (powerwise) but still the annoying misfire, today i'm going to try a new (used from my box of bits!) relay for the ecu
     
  10. Richard Gilberd Forum Member

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    okay relay didn't help,next i am going for power to the coil dropping out (ignition switch?) as sometimes i turn it over and it won't start and the rev counter doesn't move which would point to no signal or no power, i still think this is a electric problem.
     
  11. Richard Gilberd Forum Member

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    so tonight things were getting worse stalling e.t.c, so i had a brain wave, lets take the revs up to where it's really misfiring and then turn the distribtor and see what happens, well it stopped misfiring and runs like a champ, i have no idea why, i have looked at static timing more times than i care to admit and then loyally been there with my timing gun to get it just right, so what the F..k, is my knock sensor fu.kd or what, but to be honest i'm havin a Beer because after the hoops this mofo had me jumping through i think i deserve it!!
     
  12. GVK

    GVK Paid Member Paid Member

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    Seems odd but a step forward! Nice one!!
     
  13. rubjonny

    rubjonny Administrator Staff Member Admin

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    is it a genuine VW/bosch distributor? as sometimes the cheaper pattern ones make things worse as the trigger wheel can be made to incorrect dimensions
     
  14. Richard Gilberd Forum Member

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    genuine off a rp motor, did have a pattern one and that did make things worse so i sent it back, but i geuss that was the problem with that then.
     

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