R107 Workshop
Mercedes-Benz R107 · 280–560 SL · 1971–1989

Cranks but won't start

Starter spins normally but the engine never catches — no run, no stumble.

Applies to all R107 fuel-injection systems. The flow below first asks which system you have (D-Jet 1972–75, K-Jet 1976–85, KE-Jet 1986–89); KE-Jetronic gets the full detailed tree, D-Jet and K-Jet route to system-specific guidance because the test points differ. Verify spark first regardless of system.

What the diagnosis checks

  1. Which fuel-injection system does your R107 have?
  2. Confirm: 1986–1989 560 SL / 420 SL with KE-Jetronic (CIS-E, has EHA)?
  3. Strong blue spark at a known-good plug grounded to the head?
  4. Do you hear the fuel pump prime for ~2 s when you turn key to RUN?
  5. Fuel pressure at the cold-start valve > 5.0 bar?
  6. 12 V at the EZL ignition module connector when cranking?
  7. Is it a 1976–1985 K-Jetronic car (450 SL / 380 SL)?

Possible causes it points to

  • Cold-start valve or thermo-time switch
  • Low system fuel pressure
  • Fuel pump relay / OVP
  • Crankshaft position / TDC sensor
  • EZL power supply / fusible link
  • K-Jetronic (1976–1985 450/380 SL) — purely mechanical CIS
  • Early D-Jetronic (1972–1975 350/450 SL) — different system

Parts for this job

KE-Jetronic fuel system spares

Background reading

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