Nail Polish: PD vs. VP - Which is Better?

'Something I've noticed recently: Last Saturday, we picked up two Touran vehicles with 100 HP PD engines. These engines are making a knocking sound. I've also noticed this knocking on several other new cars. Our 1Z with a VEP (Variable Valve Timing) doesn't do this. Could the VEP be preventing pilot injections, or is the knocking caused by something else? Also, I've noticed that the Tourans are producing a lot of black smoke. I've never seen this on our Passat (maybe it's because I rarely drive behind it *g*). The excessive smoke would suggest that the PD engines aren't performing pilot injections. Does anyone know more about this?'

Best regards, WarLord.

Hi,

If you had just read a little bit of the old posts and the quiz, you would have come across a topic about pre-emptive injections in PD (Parkinson's Disease).
- The PD also has a pre-injection feature.
- The PD engine makes more noise (especially when cold) because the fuel injection pressure is higher than in the VP engine.
"This noise problem is common to all high-pressure injection systems. It is only through the pre-injection process that the pressure increase in the cylinder is reduced sufficiently to achieve a reduction in noise."

"With a PD engine, there's a noise that isn't related to the combustion process, but it can be mistaken for it (as it's sometimes louder than the actual combustion sound). The solenoid valves make a hissing (ticking) sound – this noise is not present during idling. This particular sound is a clear indicator of a PD engine."
If the Piezo PD elements are from Siemens VDO, then that noise will also disappear.