Mini Misfire

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ben.martins
Pico Staff Member
Pico Staff Member
Posts: 100
Joined: Tue May 16, 2017 1:02 pm

Mini Misfire

Post by ben.martins » Mon Dec 04, 2017 9:39 am

Hi all,

Interesting video here from the BMW Mini petrol engine. Misfire codes, poor performance and rough running are some of the problems but what conclusion would you have if you saw this capture?


Liteace
TwoWaves
TwoWaves
Posts: 198
Joined: Fri Jan 27, 2012 12:25 pm

Re: Mini Misfire

Post by Liteace » Tue Dec 05, 2017 11:24 pm

He could have skipped all the blar, blar, blar, life story and got straight to the point, nearly fell asleep, though I was watching a Frankie video :lol:

Technician
TwoWaves
TwoWaves
Posts: 368
Joined: Thu Apr 24, 2014 8:32 pm

Re: Mini Misfire

Post by Technician » Wed Dec 06, 2017 11:02 pm

What I think you are experiencing there with the crank waveform when the misfire occurs is the slowing down of the crankshaft rotational speed. I suppose a lot depends how you set the scope, but fine tuning the operator is able to see the crankshaft slow down up to TDC and speed up after TDC, normally, and when an ignition misfire occurs, the crank will not speed up at all, hence your flat-line at the horizontal portion. It is also worth a mention that, as we had it drummed into us at college back in the 1980's, don't assume just because a part is brand new that it is not defective, always test it, which is what we were always told.

Always check the obvious!

Ask the question, why were the plugs changed!

Did the engine have a misfire before the spark plugs were changed!

Had somebody else worked on the engine before you!

Were the correct questions asked before much time was spent looking for the fault?

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