Audi A4 1.9TDI SE Auto cranks but won't start

[A4avant1.9TDISE]

Hope I'm posting this in the right place

I have a A4 1.9TDI SE Auto 2004, it someetimes starts on the turn of the key and other times needs a little cranking with the accelerator pedal, unfortunately it sometimes won't start at all and just cranks, it's been recovered to the garage 3 times, once turning the key on and of 3 times to prime / warm the glow plugs before cranking got it started the next time it started fine when it got there and the last time it wouldn't start and the diagnostic machine said camshaft position sensor - replaced camshaft position sensor and all ok, but its done it again. Its recently had a new genuine fuel filter (I know this can cause issues) any help or suggestions most appreciated, it seems to do it when left over night and sometimes doesn't feel like its running smooth?

[nevo]

One possibility is you have a slight air leak on the fuel system drawing air in but not leaking diesel out so as you can see it ,do you park on a hill by any chance? also is your lift pump working ok when turning on the ignition?

[a8 tech]

check the cranking rpm from cold start also check the pressure pump delivery rate and pressure before the tandem pump and at the tandem pump

check the coolant, fuel and air temp senders are roughly the same from cold before cranking the engine

crank sensor fault is a red herring and only registers sporadic because the engine has not started
If the cranking rpm is below 230 to 250rpm its not sufficient and points to a weak battery or starter motor

if the fuel pressure drops overnight below .50 bar then its harder to supply instant pressure so clamp the return hose and try that also

[A4avant1.9TDISE]

Thanks for the replies,

Garage currently looking along those lines

Can anyone let us know where the pressure relief valve is which maintains the pressure in the cylinder head fuel rail? as clamping of the return necessary to hold reserve pressure at the moment

Thanks again

[nevo]

Its integral with the tandem pump where the return line attaches to the pump, there's a fitting for a pressure gauge too.

[a8 tech]

9468 :biglaugh: