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[doz]

As I struggle on with the "Growbag" I have only one item left to test really and that's the camshaft sensor. But what does it really do? Why does the ecu need to know the position of the cams? after all they are fixed in one position to the crank. So from the crank position the ecu will know where the cams are any way. If the camshaft sensor is faulty (i have no fault codes for it) will it cause all sorts of running issues? I'm struggling to track down this 2k idle problem I have. Unplugging it makes no difference to the idle.

Yours now two thirds demented
Doz.

[KillerWatt]

The camshaft sensor tells the ECU when to fire the sparks and inject the fuel.
It will work in conjunction with the crank sensor, and the info from these two (plus other odds & sods) will enable the ECU to work out what timing the plugs should be fired at as well as how much fuel to deliver.

[doz]

Yea but why cam and crank sensor? After all if you unplug the camshaft sensor the engine still run try that with the crank sensor and she'll stop dead.

[HerefordElite]

Yea but why cam and crank sensor? After all if you unplug the camshaft sensor the engine still run try that with the crank sensor and she'll stop dead.

Try unpluging the cam sensor and see if it starts

unplugging while running the ecu will just revert to basic map and still run.

Crank sensor will give engine position but ecu needs cam position for exact induction sequence to get spark right

[doz]

Cheers for that I'll give it a go.

[tmx]

cam sensor will go into limp home mode max 3.5k if the cam sensor is flagged up on the EML

Cranksensor makes the car cutout and not start when warm and even cold!

[Kevin Wood]

The cam sensor actually is only used to time the fuel injection pulses and possibly to interpret the knock sensor output on pre-DBW cars.

Although the cams are fixed with respect to the crank, for a given position of the crank, the cams can be in two positions since the cams rotate at half the speed of the crank. This is why 2 turns of the crank are needed to bring the cam timing marks back into alignment when changing the cam belt.

The cam sensor tells the engine management which of these 2 possible positions the cam is in, which allows it to work out which of the two possible cylinders is next to fire. Fuel can then be injected into the appropriate intake port (sequential injection).

Since the coil pack fires pairs of spark plugs, cam phase is not important for ignition at all, and no detailed timing information comes from the cam sensor as the crank sensor has greater resolution.

The cam sensor is probably only checked during initial engine start. Once the ECU knows the cam potition it can remain synchronised using only the crank sensor output, which is probably why unplugging it makes no difference.

If the cam sensor has failed the engine management likely falls back to firing the injectors in batches, which actually doesn't make that much difference.  The rev limit obviously does, though.

Kevin

[doz]

Cheers Kev. That's what I wanted to hear.