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So I know this is not the only case of this happening, and have read in a few other forums. But my gorgeous 560sl (86') just started running really rough the other day. I hadn't done any recent work on the car, and nothing out of the ordinary happened.

It idles rough, and has a really hard time accelerating beyond 2,000 rpm. It even died at a stop light the other day. It seems to do alright going down the highway though! And intermittently it will even idle and accelerate ok. But when its bad, its really bad.

I put a can of seafoam through it and have driven it about 300 miles since it started. The problem hasn't gone away.

Research on the forums says the following might be culprits:
1. engine temperature sensor ($60)
2. fuel distributor ($1000)
3. fuel pressure regulator ($300)
4. EHA valve ($300)

Does anyone have further input on what it actually is or ways to find out without replacing all of the above? I could really use some solid answers! Thank you!:nerd
 

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Your problems are similar to what I had when my FD was clogged, but I suppose it might have turned out to be any (or all) of your numbered culprits or a clogged catalytic converter as was first suspected.
Unless it’s a clogged CC, I think you will like me eventually require the help of a pro and his test gear to set up the fuel system properly. Why not use that pro for problem diagnosis now?
 

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I had nearly three same issue as you, and noticed the Economy gauge didnt move and was pegged in the far right, red section (NOT a political post...LOL). After some searching, I found the rubber elbow on the small vacuum line that connects to the back of the intake manifold was the issue.
 

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Thank you! Do you know if it is possible to clean out a fuel distributor?



Your problems are similar to what I had when my FD was clogged, but I suppose it might have turned out to be any (or all) of your numbered culprits or a clogged catalytic converter as was first suspected.
Unless it’s a clogged CC, I think you will like me eventually require the help of a pro and his test gear to set up the fuel system properly. Why not use that pro for problem diagnosis now?
 

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Your SL is equipped with the Bosch KE-jetronic which is an awesome system if you get to know it a bit better. It allows you for instance to diagnose a lot of the fuel injection components, for example the engine temp sensor, better know as CTS. (Coolant Temp Sensor). It does require a lot of reading to start to understand KE and the contributions of forum member H.D. are a must read.

Nonetheless, the first 2 things I would do is to test if you have any vacuum leaks. Vacuum is crucial to KE, so before you can do anything, make 1000% sure you have no vacuum leaks. Then get yourself a multi meter preferably with Duty Cycle reading, but if you have already a MM without DC then that works as well for the beginning.

Get the engine up to operating temp. With engine OFF, ignition ON, measure the Voltage between terminal 2 & 3 and 2 & 6 on the X11 socket in the engine bay and please report the results back here.

Good luck! :thumbsup:
 

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Vacuum is crucial to KE, so before you can do anything, make 1000% sure you have no vacuum leaks. :
Couldn't agree more. Eliminating vacuum leaks is an excellent starting point. And not only for KE-related issues. I noticed VERY slightly longer (maybe 1 second instead of half a second) cranking time to start. But then I noticed NO 5th GEAR!!! Cause? A split vacuum boot - one that leads from the manifold to the EZL (ignition controller). Bodge fix and normal service resumed. Permanent fix - new boot - and all's well.

And fuel consumption has improved.

So, eliminate those vacuum leaks.

Good hunting.

RayH
 

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Also check your fuel pumps. My 87 560SL kept dying intermittently until I replaced the fuel pumps. I suspect that dying fuel pumps, yes, there are two, put extra strain on the fuel pump relay since dying pumps likely draw more current as they struggle to pressurize the fuel and it burns out the transistors that feed the fuel pumps.

One of these days I’m going to put a fuse on that circuit, I think it’s the only electrical circuit that doesn’t have one and replacing a fuse is a lot easier and cheaper than replacing the fuel pump relay.

I had another intermittent starting problem after it rained or after I washed the car that turned out to be a poor ground connection on the coil. The screw on the ignition coil is fastened to a sheet metal engine compartment wall and the other side is exposed to the elements. A little rust around it can impede the ground connection. Now I always put a tiny dab of No-Ox-Id contact grease on to prevent that sort of thing.


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I will be watching this thread. All good suggestions above. I also have an 86 560SL and I am learning all I can about the KE Jetronic.

I would start by checking for vacuum leaks. A smoke machine would be the best tool. Or an unlit propane touch. Hold the nozzle around the vacuum hoses, injectors, lower throttle body. If you hit a vacuum leak the engine speed will rise.

Cleaning the ground wire connections is a simple DIY job. On the left side just next to the fuel distributor you will find a grounding terminal with about 5 brown wires. Clean those. The main ground wire is below between the frame and the engine. You will need to raise the car up to reach it.

As a matter of maintenance you could replace the distributor cap and rotor. Maybe plug wires too. Or you could at a minimum check their condition for arcing.

To me it sounds like a fuel problem. I would next check the fuel pressure, lower and system. Sorry I don't remember but the pressure specs are listed in numerous places in this forum. I need to do this as well. I rented a fuel pressure test kit from O'reilly's but unable to use it because their kit does not have a fitting to match ours.

Then on to other testing. In the Encyclopdia Germanica in the sticky above there is an excellent paper about KE-J by Isthisdave. Read that as it gives an excellent overview and test steps for you to try.

DO NOT EVEN THINK ABOUT ADJUSTING THE AIR / FUEL METER!!!!!! That is not air fuel mixture. And due to the sudden onslaught of your problem I doubt any adjustment will really do any good.

I'm doing this from my phone so I can't do an adequate search. But look for an article authored by HD. It might be in the 126 section. But he gives an outstanding intro to KE.

Baul18's thread titled "Change fuel filter now won't start" is also an excellent read and journey into testing before you spend $$$$$$ replacing parts that may or may not be bad.

Look forward to hearing your progress.
 

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