Post
by FlySpeck » Mon May 17, 2010 12:12 am
haha i know mate.
Ok, talked to a guy who is a bench technician for Bosch and lives in France....my wifes aunty has a house there and we been over before helping deco etc.
Local mayor (also postman, cop and hotelier) has a nephew, Peter, who is the bloke concerned....I heard "he works for Bosch, is pug fan" - and bingo my ears are pinned back! I got talking to him, and it turns out thus:
The injector is at fault, Bosch dont sell parts except the nozzle (which isnt the problem) to anyone, so "recon" injectors from anywhere can be just as badly worn as they only swap the nozzle (except in Bosch themselves)....scrapyards are better, or buy second hand as cheap as poss and swap them. Or pay Bosch loadsadosh to swap it out lol.
What happens is, the pin (rod) that moves up and down to let the pressurised fuel into the nozzle orifice holes (and they are only 0.0135 mm across for the anoracks) wears in its forged steel bore....the injectors use pressure balance to stay closed, as no solenoid coil could lift the needle against such massive fuel pressure, so the injector has 2 chambers, called "pressure" and "control" - both fed rail pressure fuel, so the needle actuator stays closed. The solenoid when fired, introduces a small controlled leak to the leakback pipe from the top "control" chamber, and the huge pressure in the bottom chamber (pressure chamber) surrounding the needle end, forces the needle rod upwards due to pressure difference, and this lets the fuel to the nozzle where the rail pressure forces it through.
The ecu uses pilot or pre - injection from 2k rpm to 3.2k rpm, then turns it off. What goes wrong is the worn injector allows fuel from the pressure chamber to leak up to the control chamber and hold the solenoid valve open too long or make it shut slowly, which makes the supposed tiny (1ml) pilot injection turn into a full blown spray - which is obviously wrong in timing terms, as it forces strong pre-ignition and an early combustion bang (clatter) in the affected cylinder, and hence you are hearing the cylinder not the injector itself. It is "pinking" heavily, which to a TDI / HDI just means the timing is advanced on that one cylinder due to the leaking injector.
A leakback test then shows which injectors are not admitting full pressure to the nozzle but leaking back into the control chamber and hence out to the leakback pipe.
Simply put, its good, as it means it is only an injector, which can be had cheap from france, or get a scrappy one and swap till it shuts up. So - it is pinking - its not great to have - swap a second hand injector with each one in turn, matching the injector "class" (2,3,4 etc stamped on the head of the injector) and drive it to see if you have hit the right one - or use a screwdriver or rubber tube to listen to the plastic leakback connector above each one, the bad one will clack with a heavy sound to the ear, good ones tick softly....swap the dud out - Job Done!
**btw I experimented with the 3rd piston deactivator plug off - so full rail pressure from the pump all the time instead of graduated 200 bar to 1350 bar between 2k and 3.2k rpm....it pulls stronger at low revs (below 2k) but the rattle is slightly worse low down (as expected - higher pressure at the rail sooner so earlier leakage) - oh and the injectors fire using inductive kickback from each other to charge a capacitor bank in the injection ecu like a camera flash unit, which pulses the next injector which then charges the caps again when its field collapses, ready to fire the next injector......ach you get the idea. Thats why when one injector fails completely like having an open circuit solenoid valve - the whole lot fail and the engine stops as the chain reaction is broken that produces the high voltage pulses. unusual but clever.
TaDa!!!
2001 406 HDi 90 LX saloon with moon miles...
It's confirmation day here, I've just escaped from one such party next door and if I see any more food today I'll explode. 
).
