560SL no power under load - Mercedes-Benz Forum
 
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post #1 of 7 (permalink) Old Today, 09:37 AM Thread Starter
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Date registered: Aug 2019
Vehicle: 1987 560SL
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560SL no power under load

Project car purchased on ebay. Starts up fine but struggles off the line with the pedal all the way down. Zero power...can't get up a hill. Running it for a while doesn't make a difference. Top speed about 50mph...then engine temp starts to spike until overheat. First indy swapped the fuel distributor from another SL in the shop and that didn't fix it, so he gave up. Then MB of Manhattan said compression on the engine is good but the cat was clogged and engine should come to life with a new exhaust system. They said one of the spark plugs was laying on its side so one cylinder wasn't firing. They re-threaded that so now it sits properly. They suggested I take it to an indy for an exhaust install, which I did. Indy swaps the exhaust and there is no improvement whatsoever. That indy checks the timing which is perfect, swaps in a new fuel filter which makes no difference in performance. Iíve scoured posts and found similar but not quite exact symptoms. Indy is confounded and is about to test the fuel pressure. Any ideas? Accumulator, fuel pump relay, maybe some sensor causing this?
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post #2 of 7 (permalink) Old Today, 11:16 AM
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it might be the O2 sensor.

once the engine was brought up to temp (after about 30 mins) the engine would starve for fuel stutter and not be happy. this is what i figured the issue to be and my local mechanic agreed with this. so i had the 02 sensor replaced and things really improved. it then led to having to replace both fuel pumps, filter and a fuel line because the engine wasn't starting on first try initial pressure was not ideal. since these fixes, i have had no issues.

now before all of this, i did replace my fuel injectors, seals and hoses myself. they were bad. fuel distributor wasn't the problem for me.

so when you had the exhaust replaced did you replace the O2 sensor?
my situation is not exacting the same as yours but it's worth a try.
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post #3 of 7 (permalink) Old Today, 12:28 PM
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Quote:
Originally Posted by theflow View Post
Top speed about 50mph...then engine temp starts to spike until overheat... indy checks the timing which is perfect
I'd suspect that something is still not timed correctly. Low power+overheating can be due to retarded ignition timing, which leads to slow fuel burning without putting much force on the pistons, but delivering excessive heat to the exhaust ports and valves. Perhaps have the cam timing checked too, although your mechanic said compression was fine.
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post #4 of 7 (permalink) Old Today, 01:07 PM
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Hi @theflow

Your 560SL has electronic timing. There's nothing to check or modify so that rules out that one.

A clogged cat obviously means a rich running condition.

My forum mantra for basic troubleshooting on these cars:

Have your mechanic smoke test the engine and then perform a fuel pressure test from cold to hot.

If any smoke leaks out from deep within the confines of block valley, you will need to rebuild the intake system. If the fuel pressure falls outside of spec, you will have to play with the EHA valve that sits on the distributor.

Those two tests will get you a baseline of what the underlying issues are and what needs to be fixed.

Most likely, there are some severe air leaks in the intake which the KE Jet system can't over come. These air leaks are typically what do these engines in and most owners don't want to commit to rebuilding it.
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post #5 of 7 (permalink) Old Today, 01:59 PM
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Originally Posted by okyoureabeast View Post


These air leaks are typically what do these engines in
beast, what do you mean?
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post #6 of 7 (permalink) Old Today, 02:25 PM
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Originally Posted by dugald View Post
beast, what do you mean?
Hehe, I should have said instead:

"Air leaks are what do the previous owners in."

These issues crop up and the skills needed to troubleshoot have faded from most shops' memories.

And the ones that do have it charge for it and the cost to repair scares them away which leads to new enthusiasts having to sort through them.
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post #7 of 7 (permalink) Old Today, 02:35 PM
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Quote:
Originally Posted by okyoureabeast View Post
Hi @theflow

Your 560SL has electronic timing. There's nothing to check or modify so that rules out that one.

Most likely, there are some severe air leaks in the intake which the KE Jet system can't over come. These air leaks are typically what do these engines in and most owners don't want to commit to rebuilding it.
Thanks for the explanation, I am just getting acquainted with this car, but I should have known as an '86 Audi we had years ago used a Hall-effect trigger in the distributor. But a question; if the distributor had been removed, can it be installed a tooth off? Also, seems to me that a bad enough air leak downstream of the airflow plate would not only tend to lean the mixture, but max the O2 sensor, which should be easy to determine with a Voltmeter.

Last edited by Turbo510; Today at 02:37 PM. Reason: Speculated about the distributor incorrectly
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