Attempting to repair other vendor's nozzles are like picnicking from a dumpster. Why would I do that to myself? You go in, KNOWING there's a problem, expecting filet minion? Some of these nozzles really are CRAP!
Let's assume my esteemed competitor (or one of their minions) or any of a list of 'injector repair services', put the injectors together so the pressures are at least, correct. If the pressures are within reasonable limits, you can test the validity of your nozzles yourself using VCDS. Without the two pressures being reasonably in range of 220/ 300 bar, the accuracy of VCDS testing is not valid.
When checking injectors, we use the VCDS/ engine module/ measuring blocks/ block 13 and 15; Idle balance compensation (IBC) and Fuel economy (FE).
At idle, note the values for VCDS. AHU's, the #3 is considered to be 0.0 mg/str, so all other readings are compared to the #3 relative point. For the ALH, each injector show it's own value.
The closer to 0.0mg/str each injector reads, the less IBC needs to alter the fueling in order to make the engine run smoothly. That, after all, is the purpose of the 'idle compensation'. We have found a way to modify injectors using IBC. Also, any change in one injector will change the values of others. One of the simple evaluations using VCDS is if two injectors, other than the #3 are varying wildly, switch their positions. If the change follows the injector, the injector(s) are at fault. If the readings follow the cylinder, the engine is at fault.
So, with the engine warmed up, VCDS with the blocks 13 and 15 on screen, your ALH will show readings across the 4 injectors. A positive number means the program is adding fuel. Conversely, a negative number is reducing fueling; all this to make the engine run smoothly at idle. But if I shim the top shim, which changes the pilot pop pressure up or down, the numbers in IBC will follow. The pilot pop will also change the main fueling. So, it takes some discriminative manipulation of the two settings and also, how one injector setting will alter the others. We usually start by improving the injector that is 'worst out of balance'.
In all of this, you must understand, the mg/str is milligrams per stroke; .001Liters. We are looking to make it less than .5mg/str or .0005 liters variation per each cylinder's firing stroke. Very incremental differences. For us to volume the nozzle usually takes iterations of 25 strokes, minimum to get enough volume to measure decently. Test stands will give 100 strokes. But the problem is when popping an injector on a test stand, the fuel releases into atmospheric pressure, or I refer to that as emulations, instead of the rarified pressure of a running engine, which is testing under actual operation. Put the calculations to it: 907rpm x 60= 54,420 firing strokes per hour .5 liters/ 54,420=.00000918Liters per engine revolution, or.00918mg/str at idle. Check my math. That would mean a .5mg/str difference is really quite a lot! Also, the actual mg/str read is only an estimation, at best. A reference point, more than an accurate number.
So, the pilot pop amount of fuel is extremely small; not even all of what the pilot pop can make is used at idle. Usually in the block 15, the FE will show on average, .3-.4 liter per hour (lph) fuel usage. This measurement is a 'virtual sensor' reading taken from various sensors, like the MAF, MAP and #3 sensor. If you have a reading that low, that is fine, but you don't drive your car idling everywhere.
In order to read the second stage, or main fueling, the engine's rpm should be raised to just under 1600 rpm. You will note, as soon as you hit 1600 rpm, the IBC numbers freeze. Drop below 1600 and wait about 15 seconds, they will return to 'read' condition. I don't recall for sure, but I think you may need block 10 to see rpm. If you place a proper length stick between the seat and the fuel pedal, you can accurately hold rpm at 1596, or as much rpm as possible but still have the IBC program working. So you understand, as soon as you hit 1600 rpm, the IBC program turns off. After all, you aren't idling anymore and the PURPOSE of IBC is to make sure your engine doesn't shake at idle. We have modified the use of the IBC.
Note the change in IBC numbers from those at idle. Sometimes, the change is dramatic. This is because now, at the higher rpm, the second stage is operating and you are fueling your car more similarly to driving. So, my opinion, it is a very good practice to set the shims for the main pop, and causing the injectors is to have equal flow at the higher rpm... much more important than the actual idle numbers.
So, with the engine running at a fast idle, note the FE. Usually, 1.8-2.4 lph with no-load is normal. (The FE numbers will go above what IBC can do. We often use a 2000 rpm for certain purposes.) Keep in mind, although the fueling is modified by IBC up to 1600rpm, as soon as you hit that plateau, the engine's fueling is no longer modified. Each cylinder gets whatever the injector gives it, WITHOUT IBC. That means any injector that had a negative reading, when above 1600 rpm is now OVER fueling. That is the essence of how I have used IBC to improve overall effectiveness of the injectors. You'd be amazed what a couple of .001" difference in shims will do to modify total volume.
Although you can get very precise pressures at 220 bar and 300 bar, the nozzles are made with extremely small and not always as precise as some would claim, orifices... 5 in the usual TDI nozzle. For example, the size measurement of nozzles is in um2, or micrometers squared. Examples: The original Bosch 5-speed ALH nozzle is .184um. 520's are supposed to be .216um. The fake 1019's never were the right size, but Bosch makes them .213um. The clones are more like .220um. My opinion is they turned what used to be a fuel-sipper nozzle (Bosch 1019/955) into a rebadged 502 nozzle.
Any way, variation between the orifices will change not only total volume, but spray pattern and cavitation, which is another whole chapter and verse. But it comes down to the point, FLOW is more important than exact PRESSURE. It's not the exact PRESSURE of the fuel, but the VOLUME of the fuel that is the single most important value when setting injectors.
This is yet, assuming that the intake manifold is doing it's job. By the commercial shape of the intake, the #1 and to a slightly lesser point, #2 cylinders are slightly air starved because of the radical turn (at least in the ALH Stock intake, opposite in the AHU..), and any demand to 'bend the air' around corners, will adversely affect air flow. I know the BRM intakes are lauded, but they still don't really get it done.. So, based on hydrodynamic theory, I should be setting the 1 and 2 injectors so they are slightly underfueling or get a more perfect intake manifold. I'd like to try to create a 'more perfect manifold' one of these days..
When flow is equalized, there is not one cylinder working harder than another, or overheating to the point of melting pistons. Boy, Howdy! Have we ever seen the carnage of broken and melted pistons due to extreme variations in fueling. My techniques help overcomes those issues. When examining engines that were overfueled, the greatest damage usually is on pistons 1 and 2.
Now, just because I can, doesn't mean I will. My life is FULL of things I have promised to do. There is no more of me than last year or the year before and we are required to turn away business. The waiting list is long and I have to make it shorter. I cannot accept any additional injector work at this time.