Rough to no idle

[duffelpud]

I just got my 250sl back from my local mechanic who has had it for about a month.  Symptoms are the same as when I took it in and he, in effect, threw in the towel.  Here's the situation:

- The engine is slow to start - it takes about 5-10 seconds before it will kick over
- The engine will not idle below 1800rpm; it sputters and dies
- The engine seems to run well above 2000rpm
- The rpm's have started to increase when the brake is pressed (I realize this is almost certainly a leaking brake booster), however the above symptoms existed before this development

Here are the facts:

- The automobile had been in storage for about five years with intermittent starts
- I removed, cleaned and coated the interior of the fuel tank
- I replaced all filters
- I blew out all fuel lines
- I replaced spark plugs with new NGK's
- I replaced points and condencer
- I replaced the fuel pump with a working but used 'short' model
- The mechanic pulled and checked each injector
- The mechanic checked all fuel lines and filters up to the injector pump

I've looked through and searched through the threads, but most of them seem to deal with a rough idle.  I'm not getting an idle at all.  Once the rpm's get below 1800 or so, the engine just sputters until it dies.  Usually when I start it the first time in the morning, it will run extremely rough and then die, like it's trying to keep running.

Thoughts & opinions?

[J. Huber]

I have no real answers but just wonder how you got the new points set without ever really getting the car to run close to normal. I mean how would you know if you adjusted the dwell angle correctly? This would then allow for the timing to be set... (just curious -- not criticizin'...)

Now the one thing you failed to mention was the linkage. Have you checked the geometry on this -- it is really critical.

Good luck -- I am sure this is frustrating.

[duffelpud]

Thanks for your response.  I turned the points over to the mechanic for installation, so I'm unable to answer the inquiry regarding how they were set.  I just left a message with his associate asking that question.

I don't believe the geometry of the linkage has been adjusted or checked either.  It is still set as it was when parked five years ago.  Again, I'll verify this with the mechanic.

Another point worth mentioning is that when the car does start, it initially idles at around 800-900rpms, but immediately begins dropping until the engine sputters and cuts out.  Could it be that the 'new' used fuel pump is not putting out to spec?  That's easy enough to check - 1l/15sec, correct? 

Can anyone direct me to a link regarding linkage geometry?

[Sirasila]

http://www.sl113.org/wiki/Restricted/Linkage-tour

Maybe this is it.

[duffelpud]

I heard back from my mechanic and he had this to say:

- The engine ran 'perfect' some days.  Other days it ran badly.  This seemed intermittent.
- The dwell was set between 2 and 4 degrees on a day when it was running 'perfect'.
- His opinion is that there is some kind of blockage floating around somewhere in the fuel injector pump.  He felt that adding 'Sea Foam' or something like it to the fuel might dissolve whatever was in there.

[Larry & Norma]

There have been problems, documented on this site, with fuel tanks
that have been recoated. This can clog up the 'flower pot' arrangement and
cause fuel flow problems. Just a thought.

[duffelpud]

The flow of fuel was checked and is good - it's within limits coming out of the pump and at the return line.  Special care was taken when performing the coat to use a quality substance and to execute its application according to guidance on these pages, taking special care to avoid the 'flower pot' area of the tank by carefully 'rolling' the coating around the unit so as to not clog lines.

[Andres G]

I just got my 250sl back from my local mechanic who has had it for about a month.  Symptoms are the same as when I took it in and he, in effect, threw in the towel.  Here's the situation:

- The engine is slow to start - it takes about 5-10 seconds before it will kick over
- The engine will not idle below 1800rpm; it sputters and dies
- The engine seems to run well above 2000rpm
- The rpm's have started to increase when the brake is pressed (I realize this is almost certainly a leaking brake booster), however the above symptoms existed before this development

Duffelpud,

I too have a 67 250, which I got from from the second owner in Houston, TX a couple of years ago. When I first got the car, the symptoms described in green were exactly the same as I had in my car.

These went away when I changed the electric fuel pump as well as my driving habits... Now, before I start the car from cold and after having it sit for over 1 week, I put the ignition key in the "on" position and let the pump prime the system for about 20/30 seconds before turning to the "start" position. This results in the car starting within no more than two or three turns. There is no issue once the engine is up to temperature, which is when the car starts almost immediately.

Regarding the poor idle, I had myt car tuned up by the local mercedes specialist and it now idles fine. I do believe it does have a bit more room for the fuel injection to be played with, as I can definitely smell the unburnt fuel scent coming out of the back, but the problem has been cured.

Regarding the brake booster issue (highlighted in Blue), I have recently started to notice the same issue. I've started a thread about this thinking there was a chance there may be access to rebuilding it... Have you also noticed lack of braking power in either front ends?

Thanks,
Andres G