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Old 03-22-2011, 08:48 PM
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Join Date: Feb 2011
Posts: 5
85 500SL Fuel Injection

Have a 1985 500SL/Euro that has not been driven in about six years. Car was repainted and interior totally replaced. Just now got it all back together. Engine was running fine last time it was drivable. Now it starts very easily but runs rough with extremely rich mixture. Have changed out the fuel pump and filter and got fresh fuel in the tank. Engine has very good compression and good ignition, new plugs.

My guess is that something in the mechanical fuel injection system has stuck or stopped up. Having a difficult time finding any diagnostic info. on the system. Any suggestions on an approach to solve this problem would be greatly appreciated.

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Old 03-23-2011, 08:07 AM
Join Date: Mar 1999
Location: Tucker, Ga USA
Posts: 12,153
How long did the car sit?? a year or more?

Most likely an issue with the warm-up regulator
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Old 03-23-2011, 11:18 AM
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Join Date: Feb 2011
Posts: 5
85 500SL Fuel Injection

Car was not started for about six years. It ran good before. Working on asumption that something is gummed up as opposed to a failure or adjustment. The car runs and even when warm it runs very rough with black smoke from exhaust. Compression check looked good with low of 195 psi and high of 210 psi. How would I diagnose or clean the "warm up regulator" ?
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Old 03-24-2011, 07:54 AM
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Join Date: Jan 2003
Location: Matthews, NC
Posts: 1,356
MBDOC is probably right. The "warm up regulator" or I call it "control pressure regulator" is the most common problem on these cars. (Ask me how I know. I have one). You really need a special fuel pressure guage to check the control pressure when cold and when warm. As the car warms up, the control pressure goes up which leans the mixture. One thing you can check, make sure the control pressure regulator has power and ground at the plug when the engine is running. If not, you will have the problem you have. I believe it also has a screen filter in one of the fuel line connections. You could try blowing air thru it in both directions and see if anything comes out. I really don't think you have a fuel dist problem.

Good luck

84 500 SEL (307,xxx miles)
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