1969 280se Coupe rough idle

[amerkhan]

Hi All, My 280se Coupe has always been a garage queen. I use to start it once a month. The last time i started it, the gas was smelling bad and old and it started missing. Checked the ignition spark and found it good. Cylinder 5 had no power. Checked the fuel to that cylinder and found that no fuel was coming in from the Injection pump in that line. All fingers point towards the pump. I put new gas and ran the a bottle of fuel injector cleaner but no good. What could be the possible problems with the FI pump? If clogged or sticky? How can i fix it myself instead of expensive overhaul of the pump. Please help.

[mercmad6.3]

You have just discovered why mercedes say to start the car AT LEAST once per month and get it hot and make sure you use full throttle.
What has happened is that a injector pump ball valve has become blocked with varnish from old fuel.
You need to drop the tank and get it cleaned ,not lined with anything ,Just cleaned including ensuring both lines are free and clear.
The fuel lines need new rubber hoses and the steel lines must be flushed. Spray paint thinners blown up the lines with compressed air is the best method to clean them.
The fuel filter bowl must be removed and cleaned and new filter installed.Leave the fuel tank empty for a moment while you go through the next steps;

The Pump .
[i]To clear the injector pump you need to source plain toluene.
[ii]next remove the fuel inlet pipe and rig a funnel so you pour toluene into the pump.
[iii] Crank the engine over. It won't matter if it starts,it won't harm the engine but it will destroy paint so be careful.
[iv]Turn the engine off if it runs then pour more toluene into the pump and let it soak overnight.
[v]repeat '[iii]'
[vi]reconnect the fuel lines,refill the fuel tank and run the pump (rear fuel pump)
[Vii] start the engine check your results. It will run rough until the toluene is run through.
[viii] In future use 1 liter per 100 liters of ATF in the fuel. This cleans the pump and cylinders and prevents the pump from sticking again. Always make sure you give the engine a few full throttle blasts to make sure the pump fuel rack moves through it's range.

[bwostosh]

"garages kill"

true quote from Dan Smith M-100 group

You should do the full fuel system cleaning as listed.

Tank to injector tips.