280SL Stumble Solved
This was a multi layered issue that on remediation has resulted in a beautiful powerful smooth running car.
The Car: 1969 280SL California Coupe 93,000 genuine miles. 576G/040
Tenure: Owned for 12 years, driven circa 200 miles per year. Full History.
The Problem: After 30 mins plus of driving an intermittent idling stumble which years later grew to stuttering on acceleration. This advanced to a failure of ignition at 4000 rpm and some weeks later, catastrophic backfiring and rough running without power to proceed.
The diagnosis:
This was a combination of ignition and fuel supply failure.
Part of the problem only occurred post heat transmission to engine peripherals, whilst the fuel delivery issue was constant.
The individual failures;
- 1k Resistor Lead Connectors had failed, particularly once heat had transferred to engine peripherals
- Radio Suppressor Capacitor had failed shorting to ground
- Distributor Capacitor had failed shorting to ground
- Woven Battery Earth Lead shorting on Ballast Resistor
- Rotor Button had failed and burnt
- Fuel Pump wire strainer filter end had dislodged and intermittently blocked fuel entry to pump body
The completed works:
- Tied back Woven Battery Earth Lead
- Checked Ballast power and resistance
- Checked Original Regulator with Beru Replacement (Beru later returned to inventory)
- Replaced Fuel Tank with genuine part
- Replaced Foam Tank Ring with genuine part
- Replaced Tank Filler Neck to Body Seal with Oldtimer Part
- Replaced internal boot Tank Filler Neck Cover Seal with non genuine foam sealant strip
- Replaced Fuel Tank Strainer with genuine part
- Replaced Fuel Hoses with genuine parts
- Replaced Rotor Button with Bosch genuine
- Replaced Leads and Resistor ends with Bremi Bakelite 1KOHM. Early 280SL requiring Bakelite.
- Replaced Spark Plugs with NGK5ES
- Replaced Distributor Capacitor with unit of equal value
- Replaced Radio Suppressor Capacitor with unit of equal value.
- Dismantled Fuel Pump, machined commutator, removed debris from pump body, reassembled
- Replaced Flat Head Body Fixing Bolts to fuel pump cover from Authentic Classics
- Dismantled Fuel Pressure Diaphragm and checked, reassembled.
- Removed, cleaned and tested Throttle Switch
- Removed, tested, reseated Cold Start Valve
- Cleaned and reassembled Fuel Filter
- Measured Dwell
- Inspected Points
- Inspected Distributor Body Insulation
- Inspected Distributor Shaft
Ignition/Fuel Works scheduled:
- Replace Fuel Injectors
- Replace Fuel Filter
- Replace Fuel Strainer to Bosch Short Pump (Originally Long Pump)
- Replace Distributor Cap
- Replace Ignition Switch
- Replace Battery with Bosch correct dimension
- Replace Battery Shelf Plate
- Replace Throttle Linkage Bushings and Ends
- Replace Injector Pump Gaskets (small oil leak)
- Check WRD
The learns:
- Check the basics first; leads, plugs, distributor, capacitors etc
- Refresh the fuel pump, very easy job
- Look further afield, i.e. ignition switch, regulator etc.
- Search for shorting to ground and current supply restrictions to both plugs and coil.
On this job, a big thanks to Mercedes Benz Classic Centre California, George at Authentic Classics, Patrick at Oldtimer and Kevin at McStar Australia.
Finally a heartfelt thanks to all the contributors on this forum. The knowledge base is exceptional and has helped me tremendously on my long Pagoda journey.
I hope members benefit from the above.
