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

Hesitation / flat spot under accel

Stumbles, bogs, or breaks up when you put your foot in it from low RPM.

Applies to all R107 fuel-injection systems. The flow first asks which system you have. KE-Jetronic (1986–89 560 SL) acceleration enrichment is handled by the EHA via the air-flow sensor differential pressure. D-Jet (1972–75) uses MPS + cold-start valve; K-Jet (1976–85) is purely mechanical with no EHA — different test procedure.

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. Is the bog only present when cold (first 5 min)?
  4. Air filter and fuel filter changed in the last 2 years?
  5. Does the EHA show ~10 mA at warm idle?
  6. Is it a 1976–1985 K-Jetronic car (450 SL / 380 SL)?

Possible causes it points to

  • Warm-up regulator slow to enrich
  • Worn injectors / poor spray pattern
  • EHA out of range
  • Clogged fuel or air filter
  • 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

Loading the step-by-step diagnosis…