Table of contents: Checking the fuel return flow for… ↓ Checking the fuel flow in the return… ↓ Installation of return fuel lines ↓ Checking open injectors ↓
Checking the fuel return flow for all injectors
Remove the engine casing. Disconnect the return fuel line hose "3" from the rear of the pressure reducing valve "2". Close the open end of the return fuel line with the plug "1". Lower the hose "3" (if necessary, extend it with hose "4") into a suitable container to measure the fuel consumption in the common return line. Start the engine and let it idle for 2 minutes. The nominal value after 2 minutes: from 0 ml to 50 ml. If the nominal value is reached, increase the speed to 2000-2500 rpm and check the fuel consumption in the return line again. The nominal value after 2 minutes: less than 250 ml.
If the nominal value is exceeded, this indicates a fault 1 (or several) injectors. Check the fuel flow in the return line of each injector.
Checking the fuel flow in the return line of each injector
For each individual injector, the return fuel flow has a small value. If this value is greater for 1 of the injectors than for the others, then this injector is presumably defective. Clean all connections before removing (for example, using a standard Kaltreiniger cleaner). Dry all cleaned parts. Clamp the return fuel line after the pressure reducing valve "1" with a hose clamp up to 25 mm "3094".
Disconnect the return lines from the injectors by pressing both clamps down and simultaneously pulling the locking device up "arrow". Put the hoses on the connectors of the return fuel lines of all 4 injectors. Insert 4 hoses into the measuring device "VAG 1348/2 B". Start the engine and let it idle for a few minutes. Do not press the gas pedal during the test, the engine must only idle. With the return fuel lines removed, increasing the engine speed will damage the injectors. The volumes of fuel supplied through the return lines of all 4 injectors, measured on a warmed-up engine at idle, should be practically the same. If the fuel consumption in the return line of 1 of the injectors is much higher than the others, it must be replaced.
Installation of return fuel lines
Replace the sealing rings of all return fuel line connectors. Before installation, lubricate all sealing rings with assembly or oil. Carefully place the return line connectors on the new injector sealing rings. The fitting should lock into place with a clearly audible click. After this, carefully press the clamps down. Check the tightness of the fuel system.
Checking open injectors
Clear the ECM event recorder. Remove the engine cover. Clean all connections before removing (for example, using a standard Kaltreiniger cleaner). Maintain cleanliness, prevent contamination from entering the fuel system. Check cylinders one by one. Dry all cleaned parts. Start checking with cylinder 1. Unscrew the union nut of the fuel line to cylinder 1 on the fuel rail and additionally, using the "T40055" socket wrench, slightly loosen the union nut on the injector. Plug the open nipple of the injector's fuel line. Close the open nipple using the "T40204" threaded plug. The electrical connector of the injector being checked must be on. Delete all entries from the event recorder. Take a test drive. If the injector is recognized correctly, there should be no "positive mismatch" errors in the event recorder. The event recorder may also contain other entries. Ignore these new entries in the event recorder (tracking error). After the test drive, query the event recorder. If the "positive mismatch" entry appears again, repeat the operations with all fuel rail fittings until no more error entries appear after the test drive. Follow the installation rules for all injection lines. Moisten the threads of the union nuts with fuel. Tighten the union nuts of the fuel injector lines by hand. Check the installation for internal stress. Install the high-pressure lines.
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