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Help! MOT fail. Misfire on first cylinder.

Discussion in 'Motors' started by Ultra_Extreme, 27 May 2006.

  1. Ultra_Extreme

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    Yes yes i know, its a 306, it could be lots of things. Heres a summary.

    Took it in for MOT, knew it had a misfire but was lazy. Failed emissions slightly, mechanic reckoned it was deffo the misfire because of how the carbon had risen dropping the lambda way low failing it on both counts. (also my back pads were shagged but thats another story).

    So i get it home and head to the motorfactors for my pads and some plugs. Remove the ignition coil pack (yeah 16v so no HT seperates etc) check the plugs. GREAT, i think, the 1st plug (driver-most side plug) is coked with soot despite only being 3months old. The others have that lovely tan look (healthy) so i change the set to be safe.

    Oh dear still missing. I decide to check if it's that cylinder by sequentially disconnecting the injector connections. The only one that shows no change in engine sound is the first one (that had the cack plug). So the trouble deffo seems to be that cylinder not firing correctly.

    So first things first i go to the local scrappy and get a coil pack, 2 in fact (they know me and let me return one esp if i can cert it as working or not) neither changes anything. One made it a lot worse but i suspect that it was faulty and thus giving 2 faulty cyl's on top of the existing problem. The other works directly as my original did. The odd's on them both faulting on the same point? na dont think so.

    So i move onto the injector assembly. First i switch the connectors to try and shift the fault to another cylinder. Nope its still number 1. Then i remove the fuel rail and swap the injectors. Still same problem :(.

    Any idea where i could go from here?
     
  2. triggerthat

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    I can ask my dad for you.

    He said:

    Unfortunately it is the ECU. They are very common on 306s. You can unplug the ECU and leave it over night and hope it will reset. However, majority of the time you'd have to get the ECU replaced.
     
    Last edited: 27 May 2006
  3. Enfield

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    Location: Hampshire

    Changed the leads?
     
  4. Ultra_Extreme

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    Hmm i was edging tward this. i could get an ECU in good nick from the scrappy, but its tough to get the exact one and new they are muchos expensive. Without sounding cheeky may i ask why your dad thinks this and in what capacity he is qualified to suggest it (ie is he a mechanic/peugoet mechanic, enthusiast etc)

    Cheers for the info!
     
  5. Ultra_Extreme

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    aint got no leads :) coil pack sits directly on the plugs and as ive said ive changed it twice
     
  6. triggerthat

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    He is a mechanic and has been for awhile :)
     
  7. Enfield

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    Strange!
     
  8. Ultra_Extreme

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    okey cokey, good enough for me. Ill move down that route now. I'll have a crack at the reset as a few hours outta the car should default it unless its truly damaged in some way. If it is then ill have to hunt for the same model at the scrappy which might be difficult or look for one on a forum/ebay.
     
  9. Ultra_Extreme

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    Ive looked it up and your dad knows what he's on about, it seems a common fault is that sagem coil packs cause voltage spikes that damage the ECU if a specific type. gonna look at mine and see if its this type. Can you ask him perchance if replavement ECU's always need reprogramming? ie do they hold the security alarm info etc or if i get the exact one can i switch it, im in noobsville with this bit doh
     
  10. triggerthat

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    Good luck mate. You can always get 2nd opinion. Try a breakers first as the ECU can be quite expensive.
     
  11. Dogbreath

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    Not at all, many modern cars have "Coil On Plug" ignition systems.

    U_E: It's possible you have a fouled injector that isn't closing properly so is injecting too much fuel, swapping the injector to another cylinder would confirm that, ie. does the fault move with the injector (assuming this is mulit-point injection). If that cylinder still runs badly then it's time to do a compression test to see if your problems are more expensive...
     
  12. triggerthat

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    Just spoke to him again. What year is it? If your 306 is an early model, you can probably get away with just replacing the ECU providing the model number is the same. If it is a newish one, the ECU would have to be programmed again.

    If you want his mobile number so you can have a chat let me know.
     
  13. Ultra_Extreme

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    thanks man but i dont reckon i'll need to bother him that badly :) its a phase 2 98 reg. I can get ECU at breakers and ideally would like to find the updated one that apparently prevents reccurrence of this problem.

    Dogbreath yeah m8 ive swapped the injectors but have same problem on the same cyl :( this ECU problem (SAGEM SL96-4 ECU's being damaged by voltage spikes from the coil pack) seems a common prob :( so deffo worth a look. Have the ECU out now, will try replacing later to see if the reset helps but im not too optimistic. Whats the price of an ECU reprog these days roughly?
     
  14. Dogbreath

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    The Sagem ECU failure is related to the idle control circuit isn't it?
     
  15. Ultra_Extreme

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    I believe its all part and parcel of the same system. My idle has never been right despiute many changes of stepper/map etc
     
  16. Clarkey

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    I know that on 300zx's, there is a Power transistor unit which sits between the ECU and the coilpacks, that amplifies the signal or something, anyway its a common failure. Maybe the 306 has a similar unit, if the coils are driven by the ECU directly then its time for some open wallet surgery :p
     
  17. triggerthat

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    Do you tend you leave the ignition on for along time?
     
  18. Ultra_Extreme

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    Im not sure i follow you!? how do you mean? does it turn on the starter a lot? not really, starts a beaut tbh. The missing literally came outta the blue. One day fine next poof chugging like a TD
     
  19. Sputnik II

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    You can get your ECU checked and refurb, reprogrammed. Southern Carbs and injection can do it.
     
  20. Ultra_Extreme

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    But at what sorta cost? i mean i can get an ECU for the price of a bit of trim if ya know what i mean ;) at the scrappy so nowt basically. But the reprog from Pug will be a bit. If they can refurb and reprog for reasonable money id be interested.