Hello all

Just when I thought I had this all figured out something else has gone wrong and left me stranded again. But as usual with this car, its not as straight forward as you would think.

The back story of this can be caught up on this thread that I started about 2 years ago, but only recently updated as someone else got stuck with the same problem.

https://mbworld.org/forums/s-class-w...-when-hot.html

Just when I had that sorted the car started doing more or less the same thing again. My initial thoughts were that it was the Ignition Control Module, that controls both the ignition coil packs, was starting to cause the problem again. Only this time it kept coming up with codes for misfires from various cylinders on the left side (7 to 12). So i replaced all the spark plugs with brand new NGK ones, the same as what came out. This did not solve the problem as it would get heavy misfires under heavy load and the Engine Light would start flashing until the car was switched OFF and then back ON again.

Spoke to a chap over in California, whose sometimes here on the forums, Clark Rupp of https://www.v12icpack.com/

His thought was that the coil pack was playing up, so i decided to order 2 from him and replace them both. Whilst they were in transit the car got worse and would not start at all for a few days. Had the AA come out and they confirmed it was getting fuel but no spark. Had it recovered to a local Mercedes Indy that i've used before and he got it started the same evening by simply "clearing the codes with STAR". However, that did not last long as the next day it was back to square one of it not starting again and the coil packs were stuck at customs who were not releasing them. Once they finally arrived I had them fitted and the car did not start up!!! However, after about 10 minutes of clearing the codes it finally started up and drove perfect. This was a Saturday evening. Started up and drove it around on the Sunday and no problem at all. Came to start it up on the Monday and once again it would crank but not start. It spent about 2 weeks like that until I took it back to the local dealerships and had them change the Ignition Control Unit that I had replaced about 2 years ago as it was still under warranty. They could not get it started, citing that its most likely flooded full of fuel from all the start-up failures. Bought it back local and took the spark plugs out to get rid of the fuel, however, all the spark plugs were dry and it was not flooded.

So ALL the spark plugs have been changed, both coil packs have been changed and the Ignition Module has also been changed, yet it would still not start. What else is left to change?

Today I decided to take one of the coil packs out and place it on top of the engine with some of the spark plugs inside it to see whether it was sparking on start up. Then someone suggested that rather than remove the entire coil pack and the plugs, I could just disconnect it and use one of the old coil packs and plugs. After all, we were only looking for a spark.

So imagine the picture, the right coil pack is in the engine and connected up as usual. The left coil pack is in the engine but has been disconnected, as that plug is now connected to my old coil pack which is simply just sat across the top of the engine with 4 spark plugs in it.

I thought I would crank it and get someone else to check for the sparking in the spark plugs, couldn't see any sparking, but rather weirdly, the car started up. WTF!

Yes, with just one coil pack connected the car started up. It was running rough, but obviously it was only running on half the cylinders. I move the car about 10 yards at a turtles pace and then switched it back off. 10 seconds later I started it back up again with only the one coil pack in and it started up straight away again.

Switched it off, tried the same thing a few hours later and yep, you've guessed it, it would not start again!!!

Does ANYBODY have ANY ideas at all please?

We know it starts up, but we need it to start up all the time, not when it feels like.

 

I had this issue with my W220 S600. It would crank fine when I leave the house. After a quick stop it wouldn't start. Crankshaft position sensor was replaced but didn't fixed the problem. Replaced the camshaft position sensor and the issue went away.
At the time I had the Launch Creader code reader and it showed no codes.

 

I had a similar issue with random no start conditions. Temperature irrelevant and stopped time irrelevant. Sometimes it would start and other times it would not.

In the front Sam is a relay called the terminal 87 engine relay. If you search online for the front Sam diagram you'll see which one it is.

This relay was intermittently working for me and was causing the intermittent crank no start condition I had. Fortunately there are a few other relays on there that are non critical but the same type so you can swap and try.

 

On Starter and Airmatic relays, if green Tyco A 002 542 76 19 then should be replaced with Hella A 002 542 23 19.

 

I'm dealing with a similar hot start issue on my CL550. I know it's a result of not enough fuel getting to the engine (when it's hot) but can't figure out why. I've replaced the ECU, fuel pump, fuel filter, camshaft sensors, crank sensor, spark plugs, and fuel pump relay. Any suggestions would be appreciated.

 

UPDATE

Gave it to a Merc Specialist that I have used many times before and after a week of investigating his conclusion was that the engine had lost compression. When I asked how he came to that conclusion he said he had a camera down one of the cylinders and the bores were all marked up. He sent me a link to a used engine in Germany. The only one available in Europe. So it was either a case of spending something in the region of £10,000 on it, or simply scrapping it.

I wasn't 100% content in my heart that my engine had just given up like that, i've always looked after my car very well. Anyways, on the way back from the indy, I took it to an Auto Electrician who I have also used before so he can have a look at it. I knew I was clutching at straws, but I just wanted to make sure.

He rang me 3 days later and said "I hope you're sat down". My heart sank then as I knew he was about to confirm that the engine had gone. But instead he told me it seemed the problem was the Voltage converter, I told him it couldn't be because I had just installed a brand new one from dealers only 2 weeks before. He asked me to come down and have a look as it was not putting out enough power to the spark plugs. Well, when I got there low and behold, the car was started and running as sweet as ever. I honestly thought I was imagining it, maybe the heat of the day had got to me or something. But nope, it was definitely running. In his haste he had diagnosed the Voltage Converter but it turned out there was a problem further back whereby the Voltage Converter itself was not getting enough power.

In the end it turned out to be a break in a live wire from the fuse box to the Voltage Converter. £80 later and the car runs as strong as ever. I could have kissed him!!!

Must also say that the break in the wire also caused damage to the new Voltage Converter and I had to get yet another one to make it run 100%. The thought in the end was that this small break near the fuse could also potentially have caused all the problems in the first place, the first voltage converter going bad and even taking the coil packs out with it. A VERY expensive lesson if im honest, but could have been a lot worse.

 

Yes, voltage converter/transformer is the most common problem of bad running/not starting on those cars if the coil packs are already checked. Clark rebuilds those transformers too. Or can loan you a good one to check. Replacement is probably the easiest job on S600, takes less than 5 minutes.

Be careful with other rebuilders - I had some bad experiences, those are not easy to rebuild.

 

I realize this post is almost a year old... hopefully you've pined the issue ELSE take a good long look at fuel TRIMS and consider replacing the old PCV Breather Valve (it's supposed to regulate a mild crankcase vaccum)
When its shot open it becomes a vacuum leak bypassing the throttle plate and making the engine too lean around idle rpm's.

The ECU slowly learns the fuel mixture map so once tge leak is fixed either reset ECU or give the engine 1kMi to come around with solid idle and cold start mixture.
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