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Old 09-06-2001, 08:45 PM
Registered User
Join Date: Aug 2001
Location: New Jersey USA
Posts: 28
Question HELP!!! 560sl rough engine

I am requesting help for my 560sl.

It is a 1987 560sl with 148,000 miles. The only things I have replaced are the fuel distributer and fuel filter. I have checked all of the vacuum hoses and the ignition. All is fine.

The engine runs smooth at first start when ice cold then it goes into a very low rpm fit. It looses all power but continues to run at a very low rpm almost like it is missing or untuned. When I turn the fuel/air mixture screw towards the 'rich' (clockwise) the engine smoothens out and runs OK. I know this is not a good way of fixing this problem.

The car has been operating fine after the fuel distributer install (approx 1,000 miles). This first started when I had thought the car was out of gas. I refilled the tank and it was fine. Then I started it again the next morning and again the power loss was there.

Does this condition sound like a bad fuel pump or is the fuel distributer faulty?

Any help would be greatly appreciated.
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Old 09-06-2001, 10:00 PM
Senior Member
Join Date: Apr 2001
Location: Beech Island, S.C.
Posts: 468
First of all you need to set the mixture using the proper tool hooked up to the diagnostic connector. When the correct mixture is achieved the tool should fluctuate between 45 and 55. You've probably got another problem such as a major vacuum leak or an electrical problem dealing with the engine control system. If that is the case you will need to set the mixture after the required repairs are done.
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Old 09-07-2001, 09:40 AM
Posts: n/a
Idles smooth when cold and then starts to get rough(not a regular miss like a cylinder not firing but erratic missing) as it heats up with idle changing ( not quite a surging but a slow up and down in the idle (600 rpm to 900 rpm) with random missing at irregular intervals which seems like a missing spark plug?? This is what I had on my '88 560 SEL. Drove me nuts. Changed spark plugs, wires, distributor cap, rotor, checked for vacuum leaks, did compression test -- everything. No difference. I have 180,000 miles on mine. What mine turned out to be was dirt in the metal screens in the fuel distributor that the lines to the injectors hook up to. Injector cleaners helped for a short term( not perfect, but better)-car idled smoother after being on highway with injector cleaner and got worse with city driving. The cause???? Rusted fuel lines from the gas tank! When we changed the two lines (feed and return) the feed line broke in two - it was so rusted. Changing the lines and pulling out the screens in the fuel distributor and cleaning them and re-inserting them finally cured the problem. Don't know if this is your problem -it was mine and drove me nuts for a year and a half before we found it!!!
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Old 09-10-2001, 07:55 AM
Registered User
Join Date: Aug 2001
Location: New Jersey USA
Posts: 28
560sl bogging

I will continue with more symptoms:

When the engine is warm the engine goes into a bogging type of run. When the gas pedal is depressed the engine continues to bogg; you can hear backfiring from the intake manifold.

Does this sound like the symptom of a bad fuel accumulator?

I will be checking fuel pressure (I can hear the fuel pump come on when the key is turned).
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