Checking return flow rate of injectors with engine running — VW

🧭 Before you start

Fits: VW Passat B8 (3G, 2014–)

• Special tools named: VAS 6684

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• Clean all return line connections (e.g. with commercially available cold cleaning solvent) before removing them.
• Clean all return line connections (e.g. with standard commercially available cold cleaning solvent) before removing them.
• Adhere strictly to rules of cleanliness. No dirt must be allowed to get into the disconnected fuel return lines or the open connections on the injectors.
• If one injector has a significantly higher return flow rate than the others (example (2)), it must be renewed .

🔧 Engine codes this applies to

📋 Procedure

1. Observe rules for cleanliness (see the separate procedure).
2. Remove engine cover panel (see the separate procedure).
3. Remove noise insulation.
4. Open heat insulation sleeve (5).
5. Unscrew nut (arrow B).

6. Unscrew bolt (arrow A).
7. Lay vacuum reservoir (1) with lines connected to one side.
8. Open heat insulation sleeve (4).
9. Release and pull off connectors (3).
10. Lay wiring harness to one side.
11. Unscrew bolts (arrow C).
12. Lay sender with pressure differential lines connected to one side.
13. Clean all return line connections (e.g. with commercially available cold cleaning solvent) before removing them.
14. Dry all cleaned parts.
15. Disconnect hose connection (2) at fuel return line.
16. Seal open return connection with a blanking plug (1).
17. Hold fuel return hose (2) (adding an extension if necessary) in measuring vessel to measure total return flow.
18. Start engine and run it at idling speed for 2 minutes.
19. If specification is achieved, increase engine speed to between 2,000 and 2,500 rpm for approx. 2 minutes, and check return flow rate again.
20. Observe rules for cleanliness (see the separate procedure).
21. Clean all return line connections (e.g. with standard commercially available cold cleaning solvent) before removing them.
22. Dry all cleaned parts.
23. Clamp off fuel return hose (arrow) using hose clamp up to 25 mm 3094.
24. Pull fuel return line connections off the injectors to be removed. To do this, push down connection at tabs and pull up centre piece to release. [Note: Adhere strictly to rules of cleanliness. No dirt must be allowed to get into the disconnected fuel return lines or the open connections on the injectors.]
25. Fit adapter C7 firmly onto return line connections of all 4 injectors.
26. Connect hoses of return flow meter VAS 6684 to adapters.
27. Start engine, and run it at idling speed for several minutes.
28. ⚠ Risk of damage to injectors after return lines have been pulled off. Do NOT press the accelerator during this test; the engine must only run at idling speed. — When the engine is at operating temperature and running at idling speed, the return flow rates at each of the 4 return lines must not differ by more than a small amount (example (1)).
29. If one injector has a significantly higher return flow rate than the others (example (2)), it must be renewed (see the separate procedure).
30. Carefully press connections of return lines onto injectors. The catch should engage audibly. Then press release pin down carefully.
31. Fit engine cover panel (see the separate procedure).
32. Checking fuel system for leaks (see the separate procedure).

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