Reference guide
R107 fuel-injection systems: D-Jet, K-Jet & KE-Jet
Across its 1971–1989 production, the Mercedes-Benz R107 SL wore three completely different Bosch fuel-injection systems. They look similar under the hood but share almost no test procedures, pressures, or failure modes. Diagnosing one with another's manual is the fastest way to chase ghosts. Here is what you have, how to tell, and where to start.
Common error: calling early R107s "K-Jet." The 1972–1975 350SL/450SL cars are D-Jetronic — an electronic, MAP-sensor system that predates K-Jet. K-Jet did not appear on the R107 until the 1976 model year.
Quick identification by year & model (US market)
| Years | Model | Engine | FI system |
|---|---|---|---|
| 1972–1973 | 350SL / 350SLC | M116 (3.5 V8) | Bosch D-Jetronic |
| 1973–1975 | 450SL / 450SLC | M117 (4.5 V8) | Bosch D-Jetronic |
| 1976–1980 | 450SL / 450SLC | M117 (4.5 V8) | Bosch K-Jetronic (CIS) |
| 1981–1985 | 380SL / 380SLC | M116 (3.8 V8) | Bosch K-Jetronic (Lambda) |
| 1986–1989 | 560SL | M117.967 (5.6 V8) | Bosch KE-Jetronic (CIS-E) |
ROW-market and Euro 280SL/300SL/420SL/500SL cars follow the same timeline: pre-76 = D-Jet, 76–85 = K-Jet, 86+ = KE-Jet. Six-cylinder 280SLs used K-Jet (1974–85) and KE-Jet (1986–89).
D-Jetronic (1972–1975)
Bosch's first analog electronic injection. "D" is for Druck (pressure) — manifold pressure is the primary load signal. Pulsed injectors, separate analog ECU, no airflow plate.
How to identify it
- Two black injection harnesses bundled to a large multi-pin connector at the right kick panel
- Analog Bosch ECU (silver box) bolted under the passenger-side kick panel or behind the glove box
- MPS (Manifold Pressure Sensor) — a finned aluminum box hose-connected to the intake
- Trigger contacts inside the distributor (no Hall sensor, no crank sensor)
- No airflow plate. No EHA. No fuel distributor. No warm-up regulator.
Key specs
- System pressure
- 28–36 psi (1.9–2.5 bar), regulated mechanically at the fuel rail
- Cold-start valve
- Pulses on cranking below ~30 °C, controlled by thermo-time switch
- Trigger
- Two sets of contacts in the distributor; one bank per pulse group
- Injector resistance
- ~2.4 Ω (low-impedance, current-driven)
- ECU power
- Switched 12 V through main relay; ground at intake-manifold stud
Common failures (in order of likelihood)
- MPS diaphragm leaks or coil drifts — runs rich, won't tune. The #1 D-Jet problem. NLA new; rebuilds and tested used units run $200–400.
- Trigger points in the distributor pitted, gapped wrong, or wire chafed
- ECU ground corroded at the intake stud — causes random misfire and no-start
- Cold-start valve stuck open (flooding) or seized shut (no cold start)
- Thermo-time switch in the head — controls cold-start valve duration
- Cracked vacuum lines feeding the MPS
Reference: Bosch D-Jetronic Service Information (1973); MB Service Manual Job No. 07-3. Active community at PeachParts' D-Jetronic sub-forum.
K-Jetronic / CIS (1976–1985)
"K" is for Kontinuierlich (continuous) — injectors spray continuously, metered hydraulically by an airflow sensor plate deflecting a control plunger inside the fuel distributor. Purely mechanical on early cars; later "Lambda CIS" adds an O₂ feedback frequency valve.
How to identify it
- Round airflow-sensor funnel on top of the intake with a hinged plate inside
- Gold/silver fuel distributor bolted directly on top of the airflow housing — six fuel lines fanning out from it
- Warm-up regulator (WUR) on the side of the block, two fuel lines, electrical heater plug
- No ECU on early cars. Lambda-CIS adds a small box (KE? no — frequency valve controller) but still no fuel-map computer.
- No EHA. No air-mass meter. No crank/cam sensor on the engine.
Key specs
- System pressure
- 5.1–5.4 bar (74–78 psi)
- Control pressure (cold)
- ~1.0–1.8 bar — WUR cold
- Control pressure (warm)
- ~3.4–3.8 bar — WUR fully heated
- Residual pressure
- ≥ 1.6 bar after 20 min (tests accumulator + check valve)
- Cold-start valve
- Pulses briefly on cranking via thermo-time switch
- Test tool
- Two-gauge K-Jet pressure set with shut-off valve (Bosch KDJE-P 100 or equivalent)
Common failures
- Warm-up regulator drift — slow warm-up enrichment, hard cold starts, runs rich warm
- Fuel accumulator internal diaphragm failed — long crank when warm
- Fuel distributor stuck plunger or leaking inner O-rings — uneven idle, fuel in the airflow housing
- Airflow plate not centered or sticky — lean/rich at specific positions
- Injector seals & spray pattern — heat-soaked rubber seals leak, drippy injectors
- Lambda CIS only: frequency valve seized, O₂ sensor dead, duty-cycle stuck at 50%
Reference: Bosch K-Jetronic Technical Instruction (yellow booklet); MB Service Manual Job No. 07.3. Useful community: PeachParts tech-talk; SLShop & KentBenz K-Jet walkthroughs on YouTube.
KE-Jetronic / CIS-E (1986–1989)
K-Jet's mechanical base with an electronic trim layer added. The warm-up regulator goes away and is replaced by the EHA (Electro-Hydraulic Actuator), which modulates differential pressure across the fuel distributor under the control of a dedicated CIS-E ECU. Adds closed-loop O₂, idle-speed control, full enrichment maps, and blink-code diagnostics at the X11 connector.
How to identify it
- Same airflow funnel + fuel distributor as K-Jet, BUT…
- EHA bolted to the side of the fuel distributor (small black actuator with a 2-pin connector)
- No warm-up regulator on the block — its hose port is capped or absent
- Diagnostic X11 connector near the firewall for pulling blink codes
- EZL ignition module + RPM and TDC sensors on the bell housing
Key specs (M117.967 560SL)
- System pressure
- 5.4–6.2 bar
- EHA current at warm idle
- ~0 mA ± 2 mA (closed-loop hunting); ~10 mA open-loop
- EHA coil resistance
- ~19.5 Ω
- Differential pressure
- 0.4 bar between system and lower chamber, modulated by EHA
- TDC/RPM sensor
- ~680–1400 Ω; air gap ~0.5 mm
- Diagnostic
- X11 blink codes — see /symptom/check-engine
Common failures
- OVP (overvoltage protection) relay with blown internal fuse — kills the whole system, no fuel pump prime
- Airflow sensor potentiometer dead spot — hesitation at a specific throttle opening
- O₂ sensor aged — EHA stuck at limit, fuel economy collapses
- EHA internal seal failure — fuel in the connector, drives mixture rich
- Air-flow accordion boot cracked between sensor and throttle — unmetered air, lean codes
- EZL module heat failure — intermittent no-spark when hot
Reference: Bosch KE-Jetronic Technical Instruction; MB Service Manual Job No. 07.3-0125. Most of this site's symptom flows for fuel/idle/start issues are written against this system.
Symptom flows that branch by system
These decision trees ask which FI system you have before walking you through tests — so D-Jet and K-Jet owners aren't sent down a KE-Jet path:
Corrections welcome — this page incorporates feedback from the BenzWorld R107 community pointing out the manual's earlier omission of D-Jetronic.