How injector nozzles fail question.

AnotherPerson

Veteran Member
Joined
Oct 24, 2015
Location
New Orleans
TDI
1999 Beetle
I've read some saying the nozzle opening wear and put too much fuel. Others say they put less fuel as they age. Which is correct?

I would think holes closing up would mean low power and less fuel.

Just trying to figure out because I'm setting my stock value with hammermod and will adjust vcds a little extra fuel for my stock injectors till the new larger ones get installed (need money). That way I can be back closer to stock iq.


Sent from my iPhone using Tapatalk
 

UhOh

Top Post Dawg
Joined
Dec 24, 2014
Location
PNW
TDI
2000 & 2003 Golf GLS (2005 Mercedes E320 CDI)
I'm really not sure how holes could end up closing up. Seems like a fair amount of pressure to keep them from doing so. Wear, on the other hand, I can understand, and that would tend to make the holes "bigger." Of course, "bigger" isn't something to get excited about like one does when one gets "bigger" nozzles.

I suspect it has more to do with the needles inside the injectors, their tolerances against(?) the nozzle bodies. Basically this results in a less controlled doling out of fuel, sloppy delivery and more often times dumping/dribbling excessive fuel (which, given enough deterioration, can lead to cylinder wear). And I could see poor combustion result in layering the nozzles some.

DriveByWire is the guy that can best explain all of this (and, hopefully, correct any misstatements here0.
 

AnotherPerson

Veteran Member
Joined
Oct 24, 2015
Location
New Orleans
TDI
1999 Beetle
Ended up deciding to just order them now with the hot swap option. Hoping thats the end of my poor milage once I get them installed. 32-34mpg is pretty bad :\


My vanes keep clogging no matter what after 2000-2500miles or so.
 

Drivbiwire

Zehntes Jahr der Veteran
Joined
Oct 13, 1998
Location
Boise, Idaho
TDI
2013 Passat TDI, Newmar Ventana 8.3L ISC 3945, 2016 E250 BT, 2000 Jetta TDI
Due to age nozzles flow less, the injection pump by way of the ECU commands a higher "Load Value" this effectively causes longer duration and a loss in fuel economy and higher EGT's and increased smoke output.

Why do nozzles flow less?

Heat for one. As injector age, the "Ejection" distance grows closer to the nozzles holes. This heat causes a slight distortion of the nozzle holes and this causes flow break up of the fuel passing thru them. This is called "Choke" in respect the nozzle. This can also occur with brand new nozzles that are are "Mount and Pray" without correctly setting the injector, in as little as 500 miles you overheat the nozzle and now they are ruined because of heat distortion.


The other effect due to age is erosion of the nozzles individual bores (aka holes). The channels develop erosion paths that cause cavitation channels, this results in flow break up and now the holes become restricted due to cavitation and a reduction in fuel flow but also grossly longer injection duration.



Wear inside the injectors causes erratic operation and out of balance in respect to the nozzles control. This causes deviations in quantity delivery, opening response and other factors like dispersion and ejection distances which can overheat a nozzle and further reduce its performance.

DBW LLC
www.DBWLLC.net
 

UhOh

Top Post Dawg
Joined
Dec 24, 2014
Location
PNW
TDI
2000 & 2003 Golf GLS (2005 Mercedes E320 CDI)
Cool stuff right there!
 

ebeday

Active member
Joined
Jun 19, 2009
Location
canada
TDI
2003 jetta TDI 2015 jetta TDI
Diesel fuel injector issues

From reading the posts regarding fuel injector operation, it would seem that there are varied ideas about how they actually work.
The job of the fuel injector is to turn the liquid fuel delivered to it whether by a digitally controlled unit injector (PD) or mechanical Injection pump (ALH) and turn it into a fine mist that ignites and burns in the presence of highly compressed, hot air. That is all the injector does.
It does this job by basic principles of fluid under pressure. The pump portion of the injector or the injection injection pump produces high or extremely high fuel pressure and tries to force the fuel past a needle and seat, the needle being held on its seat by a strong spring. The pressure builds up because fuel under pressure is acting on a very small area to try to unseat the needle. When it finally does unseat the needle, this is called the nozzle's opening pressure or VOP.
Once fuel passes the needle and seat, it enters the sac hole area from which the tiny orifices radiate. The orifices are drilled at specific angles to suit the engine they are intended for, this angle and the size of the orifices is critical for good combustion and engine performance.
Once the needle has been unseated, the pressure drops rapidly, the needle reseats, pressure builds again, needle unseats, again and again till delivery from the pumping device is cut off. The rapid seating, unseating is called nozzle chatter and is audible in some bench testing. The needle finally seats at the end of injection and from then until the next injection cycle seals the fuel supply from entering the combustion chamber.
Fuel injectors do wear, needle to seat wear does happen which affects VOP and chatter. Parts that affect needle lift do wear but we are talking "micro" wearing surfaces. Strong springs lose spring rate over time. Orifices do wear and become larger but microscopically. Orifices do become plugged but this is usually the result of micro beads of water contaminating the fuel, the water turns to steam in the heat of combustion but leaves residue behind.
When enough or all of the orifices plug, the nozzle tip breaks off because of hydraulic forces, injection pumps have no relief valves so the nozzle tip is the weakest point. Pressures are extreme when a nozzle tip fails.
If you have read this so far you will see that there is no place for injectors to get "dirty", they perform all their useful lives having been delivered ultra clean fuel. Understanding this, you will see why I don't get too lathered up about fuel additives purporting to "clean" dirty injectors. The tips protruding into combustion chambers get discoloured from soot but that is all.
That is all from me as well.
 
Top