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Quanta2 07-18-2018 02:48 PM

Reliability 560SL
I recently purchased a 1986 560 SL that have been stored in a heated garage for the last 19 years. The paint and interior are nearly perfect and the wife is slobbering, wanting to get her hands on the car. The problem is reliability. I removed the fuel tank and cleaned it out blew out the fuel lines replaced fuel pumps and filter as well as the screen. New battery and tires and the car started right up and ran like a striped assed ape! For a couple weeks I took it on short trips 30 minutes or less and it ran perfect. My confidence built up and I took it on the longer trip and it suddenly died at 50 minutes. It re-started and ran perfect for 20 more minutes died suddenly again, restarted and ran the rest of the way home, about 20 more minutes. I did some reading on these forums, and replaced the fuel pump relay. On the next drive it died at 50 minutes again, started right back up and ran perfect the rest of the way home. I parked it in the garage and have been on a one-month bike trip, just got back yesterday, decided to drive the car in to town for groceries. 15 minutes to town. It made it to the store running perfectly, when I started the car to go back home it was missing badly, black smoke out the exhaust and the economy gauge would peg itself to the right side anytime I stepped on the throttle. Grossly over rich. Barely made it home. I have ordered new spark plugs and wires. The car does not have the OBD port. Just the 9 pin circular port for the oscilloscope. I believe I have 2 separate issues. I know there is a ton of knowledge on this site. Does this scenario sound familiar to anyone out there? Thanks in advance for any direction. Would love to let the wife drive this beauty!

rcrmonte3 07-18-2018 05:10 PM

Have you checked the ECU? Drops in voltage to parts of the ECU caused a similar problem in my 74 450SL.

Smackrattle 07-18-2018 05:25 PM

OVP relay?

isthisdave 07-18-2018 06:19 PM


^ That

Quanta2 07-18-2018 06:30 PM

How did you address the low voltage to the ECU? Is there a relay that feeds it? Ignition switch?
Thanks for the hint!

Quanta2 07-18-2018 06:33 PM

OVP relay sounds like an easy part to try. Where is it located? Thanks

isthisdave 07-18-2018 07:22 PM


Post number five in this thread, from the General Tech section of the EGV107, our reference library.

Quanta2 07-18-2018 07:46 PM

Thanks for the location. Must be right where I changed out the fuel pump relay, behind the glove box.

rcrmonte3 07-18-2018 08:01 PM


Originally Posted by Quanta2 (Post 17491275)
How did you address the low voltage to the ECU? Is there a relay that feeds it? Ignition switch?
Thanks for the hint!

Eventually the car died and wouldn't restart. Finally found a working ECU that matched the 1 in the car. Replaced ECU. Car works fine now. There are a couple members here who might have one. But check everything else first. Also, you have to check the voltage to/from EACH terminal (pin) on the ECU. I don't think there's a relay that feeds it. Also, if the ignition has a fault, the ECU would work only when the ignition switch is fully functional. Ignition switch and circuits are easier to trace and less expensive to fix. If there is low voltage to 1 or more of the pins on the ECU, trace those circuits 1st and make any repairs. If none of the repairs help, or if there are no faults in the circuitry, it's the ECU.

Quanta2 07-18-2018 08:31 PM

Thanks for the good advice. I have a newbie question. On my 560, if it fails to start on the first try, the starter will not engage again unless I turn the key to the off position first, then rotate to start again. Is yours like this? Or is this something wrong with mine?

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