E24 6-Series

1976-1989 / Coupe / Germany

All E24 6-Series problems All workshop issues

Common Engine, M30 (633CSi, 635CSi)

6. Bosch L-Jetronic Fuel Injection Issues (Early 633CSi)

Symptoms

Rough idle, hesitation on acceleration, rich or lean running, poor fuel economy. The engine may start fine cold but run poorly once warm, or vice versa.

Cause

The L-Jetronic system uses an analogue air flow meter (flap-type) and a series of sensors to determine fuelling. After 40+ years, the air flow meter potentiometer wears, the coolant temperature sensor drifts out of calibration, and the wiring harness connectors develop resistance from oxidation. Vacuum leaks from perished rubber hoses compound the problem.

Fix

Systematic diagnosis starting with vacuum leak testing, then checking sensor outputs with a multimeter.

The air flow meter is the most common single point of failure, rebuild kits are available ($150-250) or replacement units cost $400-800.

The coolant temperature sensor (NTC type, Bosch 0280130026) is cheap at $30-50 and should be replaced proactively.

Wiring harness connector cleaning and re-pinning: $200-400 at a specialist.

Cost mentioned in fix

$150-250$400-800$30-50$200-400

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Other known issues

Critical Engine, M30 (633CSi, 635CSi)

5. Timing Chain and Tensioner Wear

Rattling noise from the front of the engine on cold start, lasting 2-10 seconds until oil pressure builds. In severe cases, the rattle persists when warm. If the chain jumps teeth, the engine timing shifts and performance drops dramatically, in worst cases, valve-to-piston contact occurs.

Critical Engine, M30 (633CSi, 635CSi)

7. Oil Leaks

Oil residue on the engine and components. Oil smell in the cabin from oil dripping onto the exhaust manifold. Oil spots on the garage floor.

Minor Structural and Body

1. Front Subframe Mount Corrosion

The front subframe mounting points corrode from road spray and accumulated grime. In advanced cases, the mount tears away from the body under braking or over bumps, causing a complete loss of front suspension geometry.

Minor Structural and Body

2. Rear Trailing Arm Pickup Point Corrosion

The rear trailing arm mounting points weaken from corrosion, causing the rear suspension to shift under load. Symptoms include vague rear-end handling, uneven rear tyre wear, and clunking from the rear when cornering.

Critical Structural and Body

3. Windscreen Surround Corrosion

Bubbling paint around the windscreen edges, particularly at the lower corners. By the time paint is bubbling, the underlying metal is often perforated.

Common Structural and Body

4. Door Bottom Corrosion

The lower edges of the doors develop rust bubbles. In advanced cases, the door skin perforates. Paint appears to blister from the inside out.

View all 15 E24 6-Series problems