1.9 TDI cam timing adjustment

Nothing against you ben but that write-up is absolute bullshit and is the first of its type that i've seen.

those slots in the cam are to ease fitment of the new timing belt by moving slack from one side of the timing system to the other NOT to adjust the cam position for performance purposes.

the EDC15 ECU controls most variations of timing and adjusts injection timing accordingly thus ruling out this muppets theory completely.

if this were true then forums would be swamped with the same threads about cam timing and performance gains on pd engines.

hes even put the wrong picture up for the timing belt route which shows he knows very little, surprised he didnt clip the valves.

its also worth noting that i've done literally 100's of PD belts so have come across most if not all the different scenarios and outcomes.

the likelyhood of this story is that the timing WAS out and he's movede it back into place (and back within the ECUs tolerence) as when the tension is applied you can move things out by as much as half a tooth.

Commencement of injection and amount of fuel injected are set by the ECU which closes the solenoid valve on the injector to start the injection stroke and then opens it again once the correct amount of fuel has been injected, dumping the rest of the pressure stroke into the fuel return line.

The pressure is not controlled by the cam. The cam provides the mechanical displacement to operate the piston in each unit injector, but the pressure at the start of each injection cycle is controlled by the springs in the injector itself.

Pre-injection starts at 180 bar, main injection at 300 bar. Once main injection has started the pressure rises further, since the injector nozzles are too small to allow the whole fuel dose to escape at once. This ensures better atomisation at higher engine speeds. The fuel pressure rise as the main injection cycle is carried out is not critical to combustion, but the efficient atomisation of the fuel dose is. Ideally the whole dose would be injected at once as a finely divided homogenous mist.

The PD cam timing is related to the inlet and exhaust valve openings, as all the cam lobes are on the same shaft. An incorrectly set camshaft will incur problems with the engines breathing, even though the ECU will be able to compensate for a certain amount of error in fuel injection.

The ECU controls the start of injection and amount of fuel injected as both these parameters are critical to the engines performance, efficiency and emission control. They benefit enormously from being controlled to a better precision than the mechanical adjustment of the camshaft can provide.

The non-PD engines, the distribution pump diesels such as ASV and ALH, have a similar items, the Quantity adjuster N146 and Commencement of injection valve N108, integrated into the distribution pump.