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Marty, Mercedes Technician
Category: Mercedes
Satisfied Customers: 53979
Experience:  Bosch Certified Master Tech. Over 35 years experience.
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I have a 1971 Mercedes 350 SL

Customer Question

I have a 1971 Mercedes 350 SL
Submitted: 1 year ago.
Category: Mercedes
Customer: replied 1 year ago.
Black smoke comes out when I press gas and car chokes. Engine was rebuilt and gas pump replaced along with all fuel lines. Also just replaced gas tank and so far 3 mechanics worked on it and it seems to keep getting worse. I'm looking for someone familiar with same car and not someone that will guess their way thru. thanks.see video
Expert:  Marty replied 1 year ago.

Hi, my name is*****'m familiar with the SL. What's your question?

Customer: replied 1 year ago.
I described the problem above, black smoke and rough running and car stalls at every light.
Expert:  Marty replied 1 year ago.

Hi Joe, I saw the description of the problem. You said 5 mechanics have worked on the car. What has been done so far?

Customer: replied 1 year ago.
Engine was rebuilt, last summer, including tank and pump and car still does not run good. I'm afraid the more mechanics that touch it the worst it will get. Again, I'm looking for someone familiar with these old SL. unfortunately all new technician know is how to replace but not how to repair. I'm not a mechanic but my guess is adjustment no more parts can possibly be replaced
Expert:  Marty replied 1 year ago.

Joe, I only get paid for my time if you leave a positive rating for my service. It's a waste of my time for me to tell you to check this and check that if you come back and tell me it's already been done. 5 mechanics have worked on the car and you think the problem is just an adjustment? I'm not so sure it's that simple. Has the manifold pressure sensor been checked for vacuum leakage? A bad manifold pressure sensor or a vacuum leak to the sensor is the most common cause of rich mixture.

Customer: replied 1 year ago.
I understand this is why I wasn't sure how useful consulting a mechanic by email.I was hoping to find someone who had a similar problem and can point me in right direction. No point in wasting your time or mine. Thanks
Expert:  Marty replied 1 year ago.
You never answered my question about the manifold pressure sensor. Has it been checked or replaced?
Customer: replied 1 year ago.
Marty,Yes that was checked couple of times and as I said to give last 3 mechanics some credit they did all the obvious checks. Car is running rich and it chokes when gas is pushed (per video) same thing happens on HWY when gas is pushed all the way, big puff of black smoke comes out and car stalls for few seconds. Car is not burning all the fuels at high RPM and I'm just getting tired and discouraged from repeated trips to various garages.I will continue my search on-line/off-line until I find the right mechanic that experienced this problem with similar car. Although you were not able to answer my question I would still like to offer partial payment for attempting to help if that is an option on this website. I'm not sure how it works since I just found it.
Expert:  Marty replied 1 year ago.

Hi Joe, I appreciate your offer. There are only a few things that influence the mixture on the D-Jetronic system. Either the manifold pressure sensor is bad or the vacuum hose to the sensor is bad or the coolant sensor is bad or the wiring between the sensor and the computer is bad or the computer itself is bad. It's also important that all of the grounds to the computer and on the manifold are good and that the charging system is functioning correctly. There isn't much else that can have such a drastic effect on the mixture. Assuming that the ignition system is good I'd have to think that your problem is among those items. The pressure sensor is adjustable for full load by cleaning out the sealing compound at the end of the sensor and turning the Allen screw clockwise to lean the mixture.

You can reply back with any questions at any time if you want to bounce something off of me.

Customer: replied 1 year ago.