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post #186 of (permalink) Old 22nd October 2009
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Originally Posted by 1938TubeStock View Post
Hi All,
Let me explain a bit about this problem. I work in the machine construction industry, where we fit proximity sensors to machines all the time, which is what the Crank Position Sensor is. The sensors have a very limited range of about 1.5mm. My brothers Clio Mk2 kept failing to start when it was warm and occasionally when cold. We fitted a new sensor which was fine for three months then the problem came back.
I took the sensor off and took it to work to test it. Attached it to an oscilloscope and all was fine, nothing wrong with it. Bearing in mind that knowing these sensors have a very limited range I decided to file out the mounting holes on the sensor bracket in an upward direction so I could position the sensor closer to the flywheel.
We rocked the car back and forth with it in first gear until the TDC mark on the flywheel was under the sensor.
I placed a 0.5mm feeler gauge between the sensor and the flywheel mark and tightened the bolts.
Since doing this to the old sensor we refitted it and the problem has never come back.
I am convinced that these sensors are mounted at their absolute maximum working distance from the flywheel. Once the engine warms up and expands by the tinyest amount, it moves the sensor to far away from the flywheel to sense it.
This also seemed to have cured the occasional cold starting problem he had aswell.
After writing this I'm suprised people are still forking out for new sensors. The sensor in the black plastic body is just a coil of wire wrapped around a magnetic core. There is no electronics so not much to go wrong with them. The flywheel passing the sensing tip alters the magnetic field flux lines so inducing a current into the sensor. The sensor has to be close enough to the flywheel to sense the magnetic flux change, which I believe is the original problem. Fillings attaching themselves to the magnetic tip could also distort the magnetic field so it wouldn't pick up a good clean pulse. From reading this forum, these sensors seem to be a problem across a wide range of Renault models. The new replacement sensor may have now solved this issue but my brothers, old original sensor is still working fine since filing out the holes. I would love someone else to try setting one up as I explained just to see if it works for them before shelling out for a new one but only if you have the confidence to do so. I set mine to 0.5mm and I suppose this is close enough for any filings to get brushed off by the passing flywheel and pick up a good clean pulse.
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