Hall effect sensors -- behaviour when failing?

[robs]

My car has recently been running really badly once it reaches about 4000rpm. On the scope the crank position sensor went gappy at those revs, so it was the culprit. I closed up its air gap some and the problem came good. The bad news is that there were already telltale marks of the wheel hitting the sensor. I rechecked the centring of the wheel and it was < 0.1mm out of round, but I noticed that the dial indicator would move up to about 0.3mm as I pulled on the crankshaft (i.e. spanner on the pulley bolt). Engine's got 300,000km on it, so might be a bit of slop there.

A couple of possibilities that strike me:

1. perhaps I originally had the gap too small; the sensor has been smacked around by the wheel and it now won't work unless the gap is small (gap is now 0.55mm and it's not happy with it any wider and the daub of paint I put on its tip has already been worn off with the quick test). Do I just need to order a new one from DIYAutoTune?
2. maybe running the sensor at 12V rather than 5V would allow me to run a bigger air gap
3. change to a different hall effect or reluctor sensor that allows a bigger gap
4. tear the engine down and replace the mains (and much else no doubt)

Happiest if it's #1 -- but is this how this sensor would fail? #2 wouldn't be bad either. Not at all keen on #4.

Appreciate any suggestions or advice.

FWIW, running MS2/Extra on a V3 board. 4 cylinder 2.2L Peugeot. 36-1 wheel, standard dizzy and coil. Very mundane, but gets along nicely all the same.

Have fun,

Rob.

[robs]

Just to clarify:

At DIY this sensor states a nominal gap of 1.5mm. I'd have no trouble if I could run with this gap. Would running with a higher voltage allow a wider gap? Perhaps a lower valued pull up resistor would do the trick?

Have fun,

Rob.

[hybrid]

I don't think the voltage will make any difference.
The magnet is affected or it's not.

The only reason it might make a difference is if the ECU is not detecting the voltage change.
If the sensor is not changing it's output at all, then changing the input voltage won't make any difference.

[jsmcortina]

Why not try a standard automotive VR sensor?

James

[robs]

I don't think the voltage will make any difference.
The magnet is affected or it's not.

The only reason it might make a difference is if the ECU is not detecting the voltage change.
If the sensor is not changing it's output at all, then changing the input voltage won't make any difference.

Fair enough. The sensor output is a square wave, but teeth are missed when the revs get up. The Hall effect is an even deeper mystery to me than magnetic flux and fields and all of that, but I can understand that more power doesn't always help.

Why not try a standard automotive VR sensor?

Laziness -- the sensor's in a pretty awkward spot and, having made the mounting bracket, I'm not eager to adapt it for something else.

I suspect that the buzzing from light contact hasn't hurt the electronics, but it may have moved the magnet further from the tip of the sensor. The car's running fine for now, and it's still just a scrape mark, not a gouge, but any contact's a worry. I'll order another from DIY if they'll stand by their 1.5mm gap claim; there won't be any contact with 3x the current gap.

Thanks for the replies.

Have fun,

Rob.