1.4 TDI Starting Issue

[Teapot]

Hi all,

This is my first post so be gentle with me.

My ex-Wifes 1.4TDI recently developed a water leak at the rear of the engine and the local garage charged her £240 to do nothing and then recommended that she spend a further £2750 on a new engine!

Suspecting it was a head gasket and knowing that she hasn't got two h'pennies to rub together I stripped the engine down and replaced it for her. As the car has always had a sketchy service history and has over 130K on the clock whilst I had the engine dismantled I also replaced the cambelt, it's tensioner and the water pump.

I'm pleased to say that the water leak has now been resolved (phew!) but it now has a starting problem.
Initially it wouldn't start at all so I scanned the forum and tried the "disconnect the cam sensor" trick and it started, albeit after putting up a bit of a fight when cold. Once it was warm, with the cam sensor disconnected, it would start every time (after a few extra seconds) and run well so I forked out £82.00 and replaced the cam sensor.

But with the new cam sensor attached it still refuses to start! Disconnect it and she fires up.

I'm baffled as I was extremely vigilant when setting the crank/cam timing so do not believe it to be this. Plus, if the timing was out how would the car run when started?

I will check the timing but as it's a bit of a faff I thought I'd check here first so see if anyone has any ideas... plus it has just started to snow and it's too cold to hold a spanner.

Am I missing something obvious?

Also, other than assisting starting, what else does the cam sensor do?

Any assistance would be gratefully appreciated.

Kindest regards,

Teapot

 

[spike]

Hi Teapot
The ECU uses the signal from the cam sensor to identify which cylinder is on the compression stroke then trigger the appropiate fuel injector as the engine is cranked while starting. If the cam position sensor fails the ECU uses the signal from the crankshaft sensor but may require several revolutions of the engine to work out the correct fuelling sequence. As far as I know the cam sensor is only used for improved starting and the engine will run happily without it.
The cam sensor picks up pulses from tags on the rim of the hub for the camshaft pulley.
Best guess is that a tag may have been damaged at some point resulting in conflicting signals from the cam and crank sensors.

Cheers Spike

 

[Teapot]

Cheers Spike,

Thanks for the advice.

I'll check the tags as soon as I can dig the car out of the snow and let you know.

Thanks again,

Teapot

 

[Teapot]

Oh dear, mea culpa...

I'd screwed up the timing. Only a incy bit but enough to freak out the ECU as the two sensors would have been sending conflicting pulses.

I think I did it when rechecking the torque of the three cam pulley bolts having already 'unlocked' the crank. This must have moved the two slightly out.

Ho hum... We live and learn, and all that.

Realigned everything again today and it fired up instantly. Wish I'd done that before forking out £82.00 on the unnecessary sensor

Cheers again for the advice,

Teapot