5.6 liter frustration 560SL - Mercedes-Benz Forum
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post #1 of 3 (permalink) Old 04-17-2019, 01:22 PM Thread Starter
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Date registered: Jul 2018
Vehicle: 1986 560SL
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5.6 liter frustration 560SL

Can someone offer a little guidance? I have a gremlin haunting me! Bought this car about a year ago, it had been sitting for 15 years in a heated garage. Went through everything I could think of, now I have a strange quirk.
The car starts perfect and idles around 750 rpm, really runs good on road until the temperature gets to normal then will start oscillating at the low throttle position. With maybe 1/8 throttle it will fade for a second or two and then come right back to smooth running. Say cruising on flat road at 40 or 50 mph, fades every few seconds for about a second. If I push just slightly on the throttle, perfect again. The duty cycle is 51% but when the fade takes effect, it goes to 75% for a second or two, then right back to 51%. This is measuring at pin #3 on X11 while driving. What should I be looking at next? What would make the voltage drop at pin #3? Have had the fuel distribution center rebuilt by Flowtech, pressures are good on top and bottom, all new rubber parts, fuel pumps and filter, fuel pressure regulator, idle control module, fuel pump module, over voltage protector, new holders and seals on injectors, air flow sensor, coolant temp sensor, throttle position sensor, O2 sensor, coil. O2 sensor puts out .47 volts. Vacuum test is solid. EHA readings are on spec at an idle. I have not drivin while monitoring the EHA. Anyone know what in the world would cause the readings at Pin #3 to drop like that?

Thanks for reading.
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post #2 of 3 (permalink) Old 04-17-2019, 02:07 PM
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Here's a random thought. Check the small wire connected to your positive terminal cable. Make sure the connection is clean and tight. On the W126 this feeds the fuel pump relay.

I'd also consider breaking and making all the connections of the relay, ovp, ecu, etc. and cleaning all the grounds in the engine bay.
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post #3 of 3 (permalink) Old 04-17-2019, 05:50 PM Thread Starter
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Will do, thank you for the reply!
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