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post #53 of (permalink) Old 25th April 2008 Thread Starter
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update (and partial cross-post)

Failed the MOT a couple of days ago on CO emissions and a seized rear brake load pressure sensor something, which after much WD40, crowbar work and bad language is now unseized.

MOT tester said that while fixing the valve clearances would reduce CO emissions it was unlikely it would bring me back to 'legal', and the next step would be to change the lambda sensor.

Sorted out the clearances and the car purrs. Have done this before (on a proper car, where the rocker cover really is a cover and you can run the engine with the it off) but I still don't really understand the process: I'm measuring a gap to tolerances of 0.05mm, but this is on the basis of visually judging the lowest point of the cam follower?!

Anyway... before doing the valve clearances I disconnected the lambda sensor. This had no effect on the engine idle (750rpm, +/- 10rpm 'flutter'). Rechecked all hoses, still no change.

Post-clearances the idle speed/flutter is still the same (sensor or no sensor), although it sounds a whole lot nicer.

Does the fact that the sensor appears to have absolutely no effect on the idle suggest that the sensor is basically not functioning, or do sensors just not affect the idle? The sensor's condition was as I imagined: bleached by water/antifreeze.

Anyway, have gone ahead and ordered a new sensor. Hopefully the sensor (52 incl VAT and P&P from Gendan) will be with me on Saturday morning, so I can fit and get re-tested. This time the car will go in warm: first test it had been sat outside the testing bay for 90 minutes...


1) Will the new sensor immediately take control of 'stuff', or does it require a proper run to assert itself?

2) I saw somewhere that the battery should be disconnected 'for a couple of hours' in order to reset the ECU : is this true? It suggests there's a backup battery in the ECU , which I've never heard of before. Is there any difference between a ten minute disconnect to fit the sensor, and a two hour disconnect?
Currently in mojolicious's garage:
2001 Ford Focus 1.9TD(d)i Estate in the incredibly luxurious 'LX' trim :)

Last edited by mojolicious; 25th April 2008 at 09:28 PM.
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