intermittent missing and loss of power

[TomsMB]

My 1966 230SL has developed an intermittent miss.  It seems to be related to trying to rapidly accelerate or when the automatic transmission kicks down to a lower gear.
 I also have difficulty keeping the car running when I back the car out of my garage.  It seems to struggle to keep running and frequently it stalls as I am trying to turn the car around in the driveway.  Also when backing out of the garage the brakes seem less effective than usual.  When I sense the car is about to stall I try putting is in neutral with the intent to try to keep it running by pressing the accelerator sometimes pumping it and even pressing it to the floor.  There is no apparent response from the engine.

Some will ask if the engine has been modified in any way.  About 15 or so years ago I changed from points to pertronix.  Otherwise the engine has not been modified.
Any suggestions will be appreciated.

[Benz Dr.]

Try disconnecting the vacuum line going to your brake booster. DON'T drive the car! Just see if runs any better. If it now runs normally, you have brake booster problem.

[Charles 230SL]

..It seems to be related to trying to rapidly accelerate or when the automatic transmission kicks down to a lower gear.. When I sense the car is about to stall I try putting it in neutral with the intent to try to keep it running by pressing the accelerator sometimes pumping it and even pressing it to the floor.  There is no apparent response from the engine..

Tom, it sounds fuel or fuel pressure related. I'd check for blockage(s) in the line from the electric fuel pump. Remember that in addition to the fuel filter (immediately prior to the fuel injection pump) there's a filter screen at the inlet to the electric fuel pump. Has the fuel tank ever been out of the car and cleaned? If not, there may be sediment or rust blocking the inlet to the electric fuel pump. 

[TomsMB]

Tank has never been out of car. I had changed fuel filters about 6 or 7 weeks ago. But I allowed the tank level to drop below a quarter of a tank and after filling the tank I wasn’t sure I would make it home.
I took the filter back off this morning and it still looked good. However I have no spare filters and now I can’t get the old one to seal properly. I have ordered new filters and will continue this effort once I can get a good seal on the center bolt.
 Of course all this also means there is about 17 gallons of fuel in the tank. Removing the tank will mean I need someplace to drain that fuel to.
I will also work on that. I have the car on a parking lift. I should be able to drain the fuel to some empty gas cans.

I will check back after solving the issues above.

[Bonnyboy]

Be careful - fuel is volatile

If you decide to drain the tank from the bung under the tank, be prepared fuel will come out in a real hurry.  I would suggest siphoning from the filler into jerry cans to take the bulk of the fuel out and then remove the fuel sender unit in the trunk (careful with the gasket) to peer inside at the flower pot.  The tank is fairly simple to remove once empty (and sender removed and vent lines and filler piece) but very heavy if fuel is in there.

I mostly emptied my tank with a siphon hose, then undid the bung and the amount of crud that came with the fuel was incredible, that was blocking my flower pot. 

Have a proper fire extinguisher handy before you start and I would suggest disconnecting the battery before you start.  A helper will make it easier or at least support under the tank so when you remove the hold down bolts it doesn't bend and drop. Clean the tank.

reinstall and Then measure the volume pumped back into the tank through the return line (its in the forum).  you need quite a bit to cool the Fuel injection pump. 

After I did all this I still had insufficient volume back into the tank so I got a new pump and still not enough volume and traced it back to a crimped fuel return line under the car.  which I cut out and replaced with new. 

Hope this helps.