kjc300

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Had to replace a plug on my fiesta Si and the plug I got from the scrappy obviously has different colour wires!! Does it matter which way round it goes??????? 2 wires 50/50!!

kjc300

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up

kjc300

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Up for some clever git!!

zvhturbo

Yes it does matter what way round they go.

If you get it wrong simply change them round.

The crank sensor wire is a special wire that has a screen round it to prevent interference. The screen must cover the entire length of the wire.

Matt

kjc300

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Cheers I have anticipated that reply and put spade connectors on it for now!!!!! Easy to swap round!! I'll solder it up proper once I find out!!

richm

kev, it may 'work' with wires either way round, but the 'wrong' way will give an ignition timing offset error - normally the sensor signal will rise as the flywheel tooth approaches, and fall as it centres on the sensor, the oposite will happen with the wires connected the wrong way. As the ECU will detect the falling edge of the sensor signal, this will give a timing error equivalent to approx half a flyweel tooth, approx 5 degrees retard from memory..

cng1

Are you sure about it detecting the falling edge? Regardless of which way round the sensor is installed the ecu will see the signal change for the leading edge, then the falling edge. Unless there's a wormhole in the cabling I can't see how it can see the trailing edge before the leading edge

richm

OK - variable reluctance (2-wire) crank sensor operation.. :-
As the target metal (flywheel tooth in this case) approaches the sensor, the output signal will start to rise due to magnetic flux change, until the sensor face is covered by the target when the signal will then fall to zero until the target starts moving away, when the signal will rise again in the opposite (negative) direction. If the target is of a similar width to the sensor, the transition from rising signal to falling signal will be continuous, passing through zero on the way.
By convention the sensor will be wired so the signal goes positive as metal approaches, and falls negative as the metal passes the sensor. The trigger circuit will be 'armed' if you like as the signal rises, then detects the centre of the target as it passes through zero ('zero-crossing detector' in electronic terms) . This provides a reliable mechanism to detect the precise position of the crank as the target will be centred on the sensor when this zero crossing condition occurs.
The convention to use the positive rising signal and subsequent fall through zero is due to there being no need for a negative supply voltage in the ECU to detect the negative signal, it can essentially 'ignore' the negative transitions as they are irrelevant.

Now if you wire the sensor in reverse, this sequence of events doesn't happen in the same way.. the target approaches and the signal goes negative, followed by a rising signal through zero as the target passes, the signal falls again as the gap between targets passes the sensor.
As you can see, the ECU now detects the falling edge sometime after the target passes..

sorry , bit long winded, I couldn't find any handy pictures to demonstrate..

kjc300

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Obviously I connected the wires wrong first go!!!

Did not start!!

Changed em over and it's now alive again!!

just have to connect them properly now to get rid of the spade connectors!!

richm

glad it's all sorted then Kev

kjc300

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