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I gave my car for service to the only BMW shop in town Rolfe Classic BMW in Canberra, ACT, Australia.

The car is under warranty routine service so the spark plugs are replaced and they put the wrong one in the wrong cyllinder.

I must have driven 2-3 kms max 80km/h with cyllinders misfiring the car shaking. Came up with a drivetrain warning too. After which i returned it to them and they fixed it.

My question is what extent of damage could this have caused to my precious car? and i love and maintain them diligently.

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  • Put the leads on the correct cylinders and probably all will be fine. A difficult thing to evaluate...
    – Solar Mike
    Commented May 3, 2017 at 12:05
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    What do you mean by "wrong one in wrong cylinder"? They fitted wrong size plugs? wrong temperature? The effects will be different.
    – Chenmunka
    Commented May 3, 2017 at 12:19
  • You need to be more specific. What got misplaced? A spark plug or a spark plug wire? Or the wrong type of spark plug? All of that makes a difference, agreeing with @Chenmunka.
    – mongo
    Commented May 3, 2017 at 15:06
  • If the car was misfiring severely, I would consider the possibility of exhaust system damage from an unburnt charge combusting in the exhaust or possible the catalytic converter. But we need a more descriptive narrative to better ascertain the probability of that. The misfire would have to be pretty severe to likely do damage, however. In my experience I have never seen damage happen from misapplication of spark plug wires. Except ego.
    – mongo
    Commented May 3, 2017 at 15:11

1 Answer 1

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When the spark plugs are out of order what happens is that the fuel/air mix in the cylinder does not burn, instead it gets blown out of the exhaust valve, into your exhaust manifold, through your turbo (presuming you have one) and into your catalytic converter. This could potentially:

  • foul the spark plugs
  • gum up the exhaust valves
  • foul the turbo (if present)
  • ruin your catalytic converter
  • damage the oxygen, gas temperature, and other sensors in the exhaust system

Any or all of these could happen over time, but it's unlikely they've happened to you in just 2-3km driven. Put the plugs in the right places and you should be good to go. In your post you said that there was a drivetrain warning, which could be an indication something is wrong, so as it's just been serviced and any work done is under warranty I would take it back to them and get them to run a diagnostic on it to make sure it's all okay.

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  • What specific diagnostic would that be? What damage are you looking for after 2-3km?
    – mongo
    Commented May 3, 2017 at 14:41
  • There's a computer system that plugs into a diagnostic port (ODB) on the car which will report any problems or look for out of spec values. Home mechanics can get an ODB reader to look for fault codes. Like I said in my answer there's probably nothing, but as it's under warranty why not have them take a look?
    – GdD
    Commented May 3, 2017 at 14:45
  • Here's my concern: poor ignition sequencing is highly unlikely to impact plugs in a short run, and certainly not gum up exhaust valves. Incomplete combustion for a short run would likely not ruin the cat or foul the turbo. Could it damage sensors? What ones on that engine? Without specific suspected damage, it only seems that running ODB diagnostics would be unnecessary work (or punishment) for the dealer. The reality is that ICE tend to suffer from bad fuel and other factors and survive. Our answers should be factual and experiential not conjecture, hence the questioning of specifics.
    – mongo
    Commented May 3, 2017 at 15:04
  • @mongo, the poster reported a drivetrain warning came up during the 2-3 km the car was driven, it would make good sense to have it checked to see what the alert was for. The dealer made a mistake and it could have impacted the car, there's no harm in checking.
    – GdD
    Commented May 3, 2017 at 15:27
  • Drivetrain warnings are typical of automatic transmission issue, and is quite common when there is rough running, and the transmission cannot properly respond to the powerplant. There may be no harm in checking except that there is a cost (to someone) to do so, and there is no indication that anything is not working correctly now. Having a headache one night does not mean that an MRI should be done.
    – mongo
    Commented May 3, 2017 at 15:38

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