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  #1  
Old 04-02-2002, 03:28 PM
Michael B
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Question "Bucking" 560SL

I have a 1988 560SL with about 130,000 miles. When I hit the accellerator to pass a car... this thing starts bucking and coughing at about 3200 RPM. On the Highway, it hits at about 70 mph... but on the sideroads... whenever the enging hits about 3200 RMP... watchout! I have to back off... then things are fine.

The car accellerates strongly... very strongly unless I really step on it.

What's the deal?

Thanks for the help!!!
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  #2  
Old 04-02-2002, 06:07 PM
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How long as it been since the fuel filter has been replaced? It sounds like a fule delivery problem under full load conditions. Could be anything from a weak pump to a dirty fuel filter.
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  #3  
Old 04-02-2002, 09:18 PM
Michael B
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Two new fuel pumps... and a new filter (new fluids all around).

Someone mentioned the "cats" but there's not a strange sound coming from the tailpipe or under the car.

Also, there's a big difference in the idle speed when in park or neutral... and in drive. Too high while in neutral (1000 RPM) and about 600 in drive. Any clue?

Thanks!
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  #4  
Old 04-02-2002, 09:31 PM
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You should ck. to see if the overload relay is okay, otherwise you might have an ignition problem wich could be causing that buck.
Have seen bad ignition coil do that. But you should always test before you replace parts. Good luck Robi
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  #5  
Old 04-03-2002, 09:37 AM
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Electrons can do anything
 
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The high idle could be a result of many things. Might need a new idle control valve (or clean it out), possible vacuum leak somewhere. But the bucking is caused from either fuel delivery or ignition problem. I agree with MERCEDESTECH you should check out the ignition system top to bottom.

I think these cars can sense an over speed condition and then cut off the fuel. I believe that is done in the fuel pump relay. There might be some component that thinks it should shut off the fuel supply. I know that the fuel pump relay does have an input signal from the ignition unit which could be used for this purpose.
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I got too many cars!! Insurance eats me alive. Dave

78 Corvette Stingray - 3k
82 242 Turbo Volvo - Manual - 270k
86 300e 5 speed manual - 210k
87 420sel - 240k
89 560sl - 78k
91 420sel - 205k
91 560sel - 85k
94 GMC Suburban - 90k
97 Harley Davidson Heritage Softail - 25k
00 GMC Silverado 1 ton 30k
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  #6  
Old 04-04-2002, 01:02 AM
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a bad or wrong fuelpump relay can cause this. if you have the means to borrow a tester, try it. good luck...paul
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  #7  
Old 04-04-2002, 01:38 AM
David C Klasse's Avatar
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Does it do this in Neutral or Park also?
When it begins bucking, is the RPM exactly the same every time? Seems to either be an electronic force, IE: fuel cut off (REV LIMITER), or a failing/fault part, etc. Is the bucking consistent? Does it sound like it's a rev limiter? Or does it sound like it's caughing/sputtering, etc?
Good luck.
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