The first thing to note is in what great condition these fuel injectors used in the 4.6 engines were after more than 20 years in use. I found that out while cleaning and testing them. For that purpose I built my own fuel injector cleaner/tester with parts I had laying around. The principle is actually very simple: a tube filled with a cleaning fluid (I used carborator cleaner) is put under pressure (about 40psi) with an air compressor and the injector is activated. I made the activation a bit more sophisticated with an Arduino, which allows four different modes (single pulse, 600 pulses at 1000 rpm, 600 pulses at 6000 rpm and unlimited random pulses for cleaning).





After two cleaning cycles, I back flushed the injectors (attached them upside down) in order to clean out any dirt which could have collected inside. Finally I tested the injectors with gasoline in order to measure the rate of flow. Results: all showed almost perfect spray pattern even at begin of the cleaning process. The flow rate was off max +/-3% between different injectors.

Installed new O-Rings (Bosch F 00V E35 007), filters & retainers (ebay) before putting the injectors back in.

Before:



After:

 

For anyone that doesn't have an arduino and the knowledge to set it up you can buy an injector testor on Amazon for about $25
12V Fuel Injector Tester Professional Ignition Fuel Injector Pulse Tester 4 Pluse Modes Powerful Fuel System Scan Tool Test Stuck/Leaking/Burnt-out Problem https://a.co/d/7f2gQE5

 

I fashioned a much more basic setup using a battery charger as a power source and momentary switch to cycle the injectors. I mounted them in an old fuel rail and pressurized it with carb cleaner. Pretty janky but it worked surprisingly well. My only recommendation would be to back flush them first to eject any loose particulate and then clean them by flowing in the normal direction.

 

I saw the tester on Amazon as well, but I had the parts already, so it just cost me some time and it was a fun project. In addition it gives me more flexibility for the cleaning modes like the random pulses which the other low cost testers don't have to my knowledge.

I did the cleaning with the filters first, then took the filters out and back flushed, so dirt doesn't get trapped by the filter. Also to note that the carb cleaner is quite aggressive and it dissolved the old O-rings partially, so always replace the parts after cleaning, not before.

 

Everyone here is so damn smart; I just send questionable injectors out to Witchhunter Peformance for cleaning.