1969 280SL Fuel System; stalls and gook in exhaust

[landyod]

The car is hard to start and will stall all of the sudden.  There is black gook coming out of the exhaust (spray and drips).  I'm told ethenol may be rusting the tank and gunking up the injectors and the mixture is too rich.  What type of modern gas is recommended?

[mdsalemi]

Landy,

Sorry, this is too brief a description in order for anyone to draw any meaningful conclusions.  Things that might be useful to know--

Is the car new to you?
When did it last drive well?
What is the service history of the car?

These cars generally run rich at cold idle, and this should lean out when warm.  When things wear in the system, they wear to a rich condition.  There are adjustments and compensations for this, that in the wrong hands can lead to poorly-engineered solutions.  It is not uncommon to have someone re-adjust all the linkages for example, to compensate for things that really need to be adjusted elsewhere.

In a "new" car, that has never run right, you need to go through the system piece by piece, and evaluate its condition.  Starting with the condition of the fuel tank and lines, the fuel pump, and then on to the fuel injection pump and injectors.  Ignition can play a big part.

The bad news is that it can take an obscene amount of time to solve, particularly if you have a car neglected; one that has been worked on by people not knowing what they are doing, or if you have multiple problems at once.  The good news is that most of the information you might need in order to get it right is here.

I'd consider checking the Tech Manual for fuel system and ignition issues...

[landyod]

Thank you, Mr. Salemi

I've had it for 4 years.  Second owner.  It sat on blocks for 11 years but was full reconditioned.  It has run beautifuly for 2,600 miles.  Idle is strong and runs very well when this is not happening.  I'm now using non-ethonol with injector cleaning solution and a marine additive to reduce/prevent rusting.  I've been chasing this for about a month with my second choice mechanic.  I probably need to get it to my favorite about an hour away?

[mdsalemi]

Look for others to pipe in here, but if I understand you correctly, this is only a cold-idle problem?  Or is it all the time now?  When warm it seems to be running well?

[ctaylor738]

Any restriction in the fuel system would cause the engine to get less fuel than it needs, not more.

Assuming no one has screwed with the car; the most common causes of a sudden over-enrichment seem (to me) to be:

- cold start valve leaking or continuing to squirt because of relay or sensor malfunction
- warm running device not working (continuing to enrich after warm-up)
- injection pump rack stuck
- restriction in air supply (unlikely)

A Search will bring up lots of info on these popular problems, except for the last one