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.

[TomsMB]

I am still trying to find the issue or issues with my 230SL.  My primary concern is the backfire from the exhaust.  It occurs as the car is coasting to a stop for example when approaching a stop sign etc.

I have drained the fuel tank.  No rust or dirt found.  The strainer was really kind of clean but I recleaned it and reinstalled it
I tested the output of the fuel pump.  Using  a stop watch and measuring output over a 15 second period.  It exceeded one liter.
I did the linkage tour and found no problems there .
Fuel filter has been changed twice.
New spark plugs installed.

The engine had been running very rich as evidenced by the black sooty spark plugs.  My latest check of the plugs indicated I may be having some effect because there were some clean spots on a couple of the plugs.

I have not touched the injection pump and have no plan to do so.  If I can find someone nearby who is familiar with the system I would welcome some advice.

I have a vacuum gauge and I plan to try to rig it up to the intake manifold to try to adjust the idle air/fuel mixture.

suggestions are welcome. 

[Vander]

I would check engine timing.

[teahead]

check the ignition system before moving onto fuel.

Check the coil, wiring, change back to points to verify pertronix went bad or not, timing as aforementioned, plug wires, cap, etc.

[Jonny B]

As another point, that I did not see mentioned in the first part of the string. There are three filters in the fuel line. There is the main cartridge type filter in the engine bay near the injection pump, a second filter at the inlet to the fuel pump, and a third filter in the gas tank at the outlet line.

[TomsMB]

I did drain the fuel tank and verified sufficient output from the fuel pump.

I assumed that if the pertonix went bad the engine wouldn’t run at all.

I connected a vacuum gauge and tried adjusting the idle mixture according to some of the guidance I have read. Initially I had no vacuum registering on the gauge. I started closing down on the adjustment and got to a reading of about 14 inches of mercury. The engine was not especially responsive as I tried to adjust the idle. I have a couple things to try this afternoon. Will report any progress.

[Bonnyboy]

You mention that there was a sufficient output from the fuel pump -  make sure you check the volume of fuel at the point where the fuel goes bank into the tank.  That way you know the system is clear.
   

[TomsMB]

I will check the return line to the fuel tank.
A local mechanic looked at it and suggested there may be a vacuum leak he was hearing. I will also check that out.

[Runale]

I had some idling issues which were quite similar. It turned out to be a leak in the Csv which completely distorted the tuning.

I cut the supply to the Csv and retuned the warm engine.  The vacuum responded, backfiring reduced and the accelerator went back to normal without roughing idle once released.

[TomsMB]

i will disconnect the cold start valve and see if it helps. Thanks

Many people i have discussed this with suggest it is a timing issue.  I would love it to be that but I am not limber enough or smart enough to hold a timing light on the crankshaft damper and see the timing marks.  between the hoses and belts and the hood I can't see down there.  how do the rest of you do it?

[TomsMB]

I gave up on setting the timing using a timing light. If you can’t see the harmonic balancer while aiming the timing light and adjusting the distributor it is really frustrating. So after checking almost everything else that was suggested here, I decided to try making minor adjustments to the timing blindly. It worked. I made my changes by rotating the distributor about an eighth of an inch. After I felt it was running much better. The idle air adjustment started responding as I thought  it should.
I ran the car about 100 miles yesterday with no problems. I am just gonna drive it and enjoy it.
Thanks everyone for your inputs. I learned a lot.

[Cees Klumper]

Many people i have discussed this with suggest it is a timing issue.  I would love it to be that but I am not limber enough or smart enough to hold a timing light on the crankshaft damper and see the timing marks.  between the hoses and belts and the hood I can't see down there.  how do the rest of you do it?

Hard to explain in words, but first of all I have a white-out mark on the harmonic balancer/dampener to make the timing mark easier to see. Then I aim the timing light 'just so' from the top, in between hoses/engine block, and this way I can see it very clearly against the pointer, allowing me to relatively easily adjust timing with one hand rotating the distributor while holding the timing light aimed properly. I've done it many times, and can't recall it being really difficult - but I do have to hold it in a very specific position pointing down in between several 'items'.
It's a bit scary revving the engine to 3000 or so RPMs while hanging over it holding the timing light (to check the advance etc) but it's do-able.
Good that you seem to have addressed (most of if not all of) the issue.

[TJMart]

Hard to explain in words, but first of all I have a white-out mark on the harmonic balancer/dampener to make the timing mark easier to see. Then I aim the timing light 'just so' from the top, in between hoses/engine block, and this way I can see it very clearly against the pointer, allowing me to relatively easily adjust timing with one hand rotating the distributor while holding the timing light aimed properly. I've done it many times, and can't recall it being really difficult - but I do have to hold it in a very specific position pointing down in between several 'items'.
It's a bit scary revving the engine to 3000 or so RPMs while hanging over it holding the timing light (to check the advance etc) but it's do-able.
Good that you seem to have addressed (most of if not all of) the issue.

Do you have a helper hold the throttle at 3000 RPMs while you get in the engine with your timing light or is there a way to somehow keep the linkage set to 3000 RPMs? I wanted to check my timing at 1500 and 3000 RPMs but don't have a helper to keep the RPMs at 1500 and 3000.

Also if your vacuum is good, will your timing, if set correctly at idle, be correct at 1500 and 3000?

Tony

[Cees Klumper]

I don't have a helper operate the throttle, I do it by manipulating the linkage with my free hand while aiming the timing light. I suppose the system, if working properly, will make the advance move sufficient if timing is set right at idle, however that is what you want to verify by revving to 3,000 rpm, and watching the timing advance properly.