Mercedes KE-Jetronic "Crank No Start" Solved: Differential Pressure & EHA Tuning W126

Crank no start troubleshooting on KE Jetronic 4, 6, and 8 cylinder cars 1. Is the OVP relay ok? Fuse(s) blown? 2. Fuel pump relay ok? Check by jumping terminal 7+8. Listen for pumps to come on. Are both running? 3. Crank shaft position sensor CPS: 680-1200Ohm 4. Fuel pressure 6-6.4Bar, delta 0.4Bar, screw in rich; out: lean 5. Fuel filter plugged? 6. Fuel filter in distributor plugged? 7. Return fuel line plugged at tank? 8. Fuel pressure regulator/accumulator busted? Typically a hot start problem. 9. Mass flow sensor potentiometer: 0.7V at idle position 10. Mass flow plate position: at lip in housing and 1-3mm play until it hits the distributor pin, little over a mm works great. Measure with fuel pressure on. That is for a low mileage car though. No flow – no gas at any of the ports. Disconnect fuel lines and push on mass flow plate. Is fuel coming out evenly? Distributor nut 0.5mm below surface not 1mm. Main plunger needs to move freely. 11. Idle control valve in good shape? 12. Check vac gauge in cluster when cranking? Does the needle even move? 13. Vac leaks? 14. Injectors: Plugged? Worn? 15. Ignition coil: does it have power? What is the primary and secondary coil resistance? 16. Spark at main cable? 17. Spark at cylinder? 18. Spark plugs 19. EZL? 20. O2 sensor? 21. ECU bad? Video Chapters [00:02] Introduction: Managing expectations and avoiding "part-cannon" repairs. [02:14] Testing the Air Mass Flow (AMF) Potentiometer voltage. [04:22] The Ether Test: Verifying ignition vs. fuel flow. [06:03] Distributing Justice: Checking fuel flow at individual injector ports. [07:40] Understanding the Air Flap: Resting position and "zero point" basics. [10:00] Diagnostic Anomaly: Why the engine only runs with a jumped relay. [12:30] Replacing the Electro-Hydraulic Actuator (EHA) valve. [14:27] Success: The engine fires up with a jumper wire. [17:15] Technical Deep Dive: Measuring and setting differential fuel pressure. [19:15] EHA Calibration: Making precise 1/4-turn adjustments. [20:16] Final Validation: Achieving the target 0.4 bar (400 mbar) difference. [23:14] The Master Checklist: 20+ points that can cause a no-start. [25:39] Hot vs. Cold Start Issues: Accumulators and cold start valves. Video Summary Ralf emphasizes that over 20 different issues can cause a "crank-no-start" on these classic models, and the worst thing you can do is start throwing parts at the problem [00:52]. This episode is a masterclass in methodical elimination. Key Technical Highlights: Ignition Verification: Before diving deep into fuel, Ralf uses an ether (starting fluid) test to confirm that the ignition system is healthy enough to run the car [04:22]. The "Jumped" Reality: Ralf discovers that while a new fuel pump relay was initially blamed, the car would only run consistently when the relay was bypassed (jumping terminals 30 and 87) [10:38]. This highlights that "new" aftermarket relays (often labeled "Made in China") can be defective out of the box [20:54]. EHA & Differential Pressure: The breakthrough comes when Ralf measures the differential pressure between the upper and lower chambers of the fuel distributor. He targets a 0.4 bar (400 mbar) difference [18:20]. Even "preset" EHA valves often require a precise 1/4-turn adjustment with a 2mm Allen wrench to suit a specific car [19:33]. Air Flap Sensitivity: Ralf notes that the air mass flow sensor plate should have only 1–2 millimeters of free play before it hits the fuel distributor's piston [08:11]. If this is misadjusted, the car will struggle to start regardless of fuel pressure. The "Bunny Trail" List: In the final summary, Ralf lists critical components to check, including the crankshaft position sensor (aiming for ~780 Ohms), the cold start valve, and the fuel accumulator for hot-start issues [25:39]. Video URL:    • Mercedes KE-Jetronic "Crank No Start" Solv...