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 Posted: Thu Sep 27, 2012 9:49 pm |
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Joined: Feb 07, 2010
Posts: 2949
Trade Rating: +6
Location: Athens, Greece
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OK, if a spark is NOT happening that's easy, no current pulse at the line for that spark-plug.
(But they are also fired in pairs due to wasted-spark scheme..)
If a spark IS happening and an injector coil is NOT open-circuit what other means does the ECU have of detecting specific-cylinder misfire?
The O2 sensors are very slow response so I can't imagine them being of any use.
The knocking sensor (essentialy a mic) combined with crankshaft position sensor would also seem a bit far-fetched..
So how's it done? 
I searched on-line but I can't seem to find good info on this and it could be quite useful
to know in interpreting trouble-codes I think.
Cheers.
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| 1.4i, 2001, 3-door, China Blue
Repair safely - Drive safely | |
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Posted: Fri Sep 28, 2012 1:20 am |
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Joined: Aug 20, 2011
Posts: 271
Trade Rating: +4
Location: worcestershire
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The ecu knows how many teeth should pass through the crank sensor for each given firing stroke (as the piston is coming back down) if there's s misfire there is no force pushing the piston down therefore it would move much slower thus less teeth passing through the crank sensor in a given time.
The crank sensor will know which cylinder was firing because there is a notch or some kind of mark to represent TDC on no. 1 cylinder and can work out from this which cylinder was firing when the misfire was detected
That's essentially it but someone might be able to explain abit clearer
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Posted: Fri Sep 28, 2012 3:59 am |
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Joined: Feb 07, 2010
Posts: 2949
Trade Rating: +6
Location: Athens, Greece
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If the crank position sensor is reading teeth as well as the notch, that makes sense
because it could be possible to detect a slow-down of the pulse train in between..
In fact I think the 'notch' is a missing-tooth, but could this way be accurate enough to assertain misfire at various RPM?
What about sudden changes due to loading of the engine by the gearbox, bumps on the road etc?
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| 1.4i, 2001, 3-door, China Blue
Repair safely - Drive safely | |
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Posted: Fri Sep 28, 2012 4:16 am |
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Joined: Aug 20, 2011
Posts: 271
Trade Rating: +4
Location: worcestershire
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Sometimes it's a missing tooth sometimes it's a small cut out load on the engine would also effect ignition timing, air flow and various other things so the ecu would understand but when there's an anomaly such as one piston slower than the rest it detects there's something wrong
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Posted: Fri Sep 28, 2012 6:03 am |
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Joined: Feb 07, 2010
Posts: 2949
Trade Rating: +6
Location: Athens, Greece
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Alright, cheers for reply and any further info/thoughts are welcome.
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| 1.4i, 2001, 3-door, China Blue
Repair safely - Drive safely | |
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Posted: Fri Sep 28, 2012 6:07 am |
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Joined: Feb 08, 2010
Posts: 10151
Trade Rating: +12
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Posted: Fri Sep 28, 2012 6:16 am |
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Joined: Feb 07, 2010
Posts: 2949
Trade Rating: +6
Location: Athens, Greece
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Cheers John, that settles it then:
"No combustion of the fuel mixture in one engine cycle results in the decrease of the torque and
the crankshaft instantaneous rotational velocity value (fig. 1). Crankshaft position sensor CPS ..."
Wicked document that.
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| 1.4i, 2001, 3-door, China Blue
Repair safely - Drive safely | |
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Posted: Fri Sep 28, 2012 1:45 pm |
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Joined: Feb 10, 2010
Posts: 4266
Trade Rating: +4
Location: Palestine
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Very good link,well explained 
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Posted: Fri Sep 28, 2012 1:45 pm |
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Joined: Feb 10, 2010
Posts: 4266
Trade Rating: +4
Location: Palestine
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Very good link,well explained
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