Technical Flywheel Sensor Replacement

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Technical Flywheel Sensor Replacement

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I need a new Flywheel Sensor for the UT. Have been quoted £50 by the dealers which seems pretty steep any suggestions for a cheaper place? Could chance the scrappies but would rather know I was getting a good sensor. Have tried shop4parts and the item has been delisted on their system. Interestingly if the car was the CAT model the sensor is only £30.

Anyone know if this sensor is common to other cars?
 
Hmm, I wonder what the difference is. It cant be much as they are all generic, as long as it fits it will work. The gearbox/flywheel is the same AFAIK so it may only have a different plug or somehting.
 
Flywheel Sensor Replacement UPDATE

Well the UT is now running again. New Flywheel sensor installed and she starts on the button. Only cost £60 inc VAT ouch. I'm convinced that this sensor has multiple part numbers some which would've been cheaper.

My problem was the car wouldn't start, car turned over on the starter, petrol pump active - could hear it prime - but the car wouldn't fire. checked distibutor was turning and the cap was good. Checked for spark none. Anyway I followed the diagnostics within the Haynes manual and all checked out fine according to Haynes - including the flywheel sensor; resistance in range.

Scratched my head and eventually called the RAC who went through all the basic checks I'd done and confirmed no spark and no injection, immediately he thought crankshaft sensor on the basis that the ECU didn't know the engine was turning over and therefore not sparking or injecting. Discounted the coil which was my guess and also the ECU - he reckoned it was very unlikely either would fail. For some strange reason the UT has a sensor on the pulley (TDC) and one of the flywheel (Engine Speed), anyone know why? RAC thought limp-home but the fact the car wouldn't run with one faulty discounts this I think. Again checked resistance of both sensors and fine. Finally I think he checked the voltage while I turned the engine over, the crank pulley was fine but flywheel out of limits. Unfortunately I can't remember exactly how he checked this so if anyone knows would be good for future reference.

The sensor was a bit of a pain to fit, the UT has so many pipes and the sensor is buried under half of them it seems.

So if your UT turns over and won't start check both these sensors are working and don't assume that the resistance confirms that are working correctly! If I'd followed the Haynes manual I'd now be buying a new ECU instead.

PS Both the RAC and Pipers of Maidstone were very helpful and Pipers also had a reasonable deal on filter and Selena oil (not 20K) both for £20 including the VAT.
 
Re: Flywheel Sensor Replacement UPDATE

Interesting! Lots of useful points there. Do you think, if the resistance was correct, that it could have been just the air gap that was stopping your old flywheel sensor from functioning? Often (though probably not in your case) it's just the connector which has a hard life hanging around under the coolant tank, above the gearbox.

Thanks for posting this info... I'm fairly certain it applies to the Mk1 as well...

The Haynes manual does quite a good job of enunciating the various sensors... I think the two sensors (crank angle and speed sensor) are both for the ignition system? One sets the timing (crank angle, near crankshaft pulley) while the other sets the advance (engine RPM counted from flywheel teeth).

While it would theoretically be possible to get the engine RPM from the crank angle sensor, I suspect it may not be accurate enough. And as for the flywheel sensor, unless the flywheel had an intentional missing tooth, there would be no crank-angle sensing possible!

Another possibility is that the two sensors are necessary because the fuel injection and ignition are two separate ECUs (unlike, say, Bosch Motronic which combines them). In the Uno Turbo, the ignition is Magneti-Marelli while the injection is Bosch. But, I don't think the injection system actually has any engine speed input at all? I wonder how it 'knows' how often to spray fuel in? (The quantity of fuel depends mainly on the airflow meter and the coolant temperature sensor - but I don't know what controls the injection timing.)

Cheers,
-Alex
 
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Re: Flywheel Sensor Replacement UPDATE

Resistance testing is quite standard but its not full proof. You need a scope to check them properly. This is beyond a haynes manual. Even more advanced books wont have scope signals to compare. You can test that they work (but maybe not working correctly) with an AC multimeter. You may get 0.5V or so when cranking. If its dead its likley something is wrong.

Crank sensor is a reference for TDC, so the ECU knows the timing of the engine. RPM sensor gives RPM. The Digiplex systems on Tipos etc combine these in 1 sensor. But its a bit more complicated.
 
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