Good morning all,

I have a situation with my 1990 Mercedes 560 SEL (221,000 miles). In the process of restoring this beauty to its original operating glory, I have been chasing a series of fuel and mechanical issues. The final hurdle involved the fuel distributor. I purchased a used unit that was supposedly in good working order off of ebay. After having the unit put on it was discovered there was an excessive amount of fuel being dumped into the engines and cylinders.My mechanic cleaned up all of the excess fuel and I was supplied a replacement unit. After installing the replacement, the engine now has a knock. My mechanic mentioned that the excess fuel may have damaged the engine and that a replacement engine may be required.

My questions

1. Does this pattern of thought make sense?
2. Can the engine be repaired, or is replacement the best answer?
3. The transmission has lost reverse. Am i better to buy a replacement for both?
4. Does anyone have or know of a good replacement unit?

I would greatly appreciate any input that is offered.The car is in excellent shape inside and out, minus the problems mentioned.

Thanks for your time,

Ron
Richmond, VA

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Fuel in the oil can cause damage but not in the short term. Has the oil been changed after this? If the oil is still thin it can make a used but still serviceable engine noisy. What ever you do, run the motor as little as possible until this gets takes care of and don't run it fast. Sometimes bearings can be changed to freshen up the motor.

Also, I "think" these motors had timing chain guide issues and will make noise.

Ron, I can only answer your first question. The answer is NO, doesn't make sense. I can't answer any of the other questions without a lot more information, so I would like to ask if you don't mind.

1. What is the history of the car? Where you driving the car before you had this problem with the fuel dist? Why was it replaced?

2. Did the engine run with the first replacement dist? If so, how long did it run? The engine holds 2 gal of oil and it would take at least 2 gal of gas in the crankcase and run a long time to cause damage.

The most common problem on these engines is the timing chain guides breaking and causing the timing chain to jump timing which causes the pistons to hit the valves in the left head and bending them. Most other problems are minor, just hard to diagnose sometimes.

Help us out with some more information and I am sure you can get all the help you need.

PaulM

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84 500 SEL (307,xxx miles)

Good morning and thanks to you both for you feedback. It seems the timing chain related issues may be the culprit. My mechanic is working on it and determined the rods and etc are good.

The history on the car includes purchasing it and it had been sitting for a year or so. After making the purchase, I lost my job and it sat for some time. When attempting to get it running, there was a fuel issue and starting issue. My mechanic identified the cold start valve was not getting power. After replacing several items (fuel pump relay, fuel pumps, OVP Relay, etc) my guy hot wired the cold start valve to a rocker switch on the console. Once getting the car started and running, it ran rough at idle and wasn't showing even fuel production out of the distributor.

We replaced the fuel distributor with one off eBay. The car started and only ran for a short period. Htis is when it was discovered that excessive amounts of fuel was dumped into the cylinders. He cleaned up this issue and replaced the porly working distributor with a replacement.

After starting the car he hear the knocking sound and immediately turned the car off. Upon restarting it on another day, the knocking sound didn't begin until the engine warmed up. He checked it out and listened ot engine and traced the noise. This lead him to the tension-er area.


I hope this info helps

Ron

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Ron, the cold start valve only gets power when the starter in engaged. It gets its ground from a sensor in the intake close to the valve if the engine is cold. Once the engine is warmed up, the cold start valve is not used again until the engine is cold again.

Now, this is very important.

The first thing I would do is pull the valve covers and check the cam timing. If it is off by more than 5 deg, change the guides and chain. If timing is 0 to 5 deg then look at the plastic chain guides in the heads (easy to see). If they are dark brown, replace the guides in the heads and the chain tensioner rail.

If the guides are white or very light brown then you can focus on the tensioner. It has a spring that pushes in on the tensioner rail and once the engine is running, oil pressure also pushes. I have never seen one go bad, but I am sure they can. Also, look down in the right head and you should be able to see the tensioner rail with a white or light brown plastic covering. If the covering is missing or partially missing, replace it.

PaulM

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84 500 SEL (307,xxx miles)

Alright now Paul for the awesome information. I will pass it on to my mechanic. I will keep you posted.

Thanks

Ron

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Can anyone show me what the cold start sensor looks like?

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And even at that, the cold start valve only turns on at near freezing temps,only when the starter is engaged and only for a few seconds. The thermo time sensor regulates the cold start.

The warm up fuel pressure regulator takes care of the choke function for most of the temperature range.

Ron, what I said about the cold start valve was correct in that it only gets power while starting. But I was wrong about the thermo time sensor controlling it. On the generation 2 gas 126 cars the cold start valve is controlled by the fuel pump relay. There is no thermo time sensor. Every thing else said is correct. Sorry for that, I jump the gun sometimes and describe how my car works, a generation 1 1984 500SEL.

One thing we all need to keep in mind is that car designers changed the electrical system in cars more often than they changed there underwear. Believe me, I have been working on electrical problems on cars for over 50 years and one thing I have learned is THINGS CHANGE.

Still, please check the timing chain and guides. If a guide breaks because it is old it can destroy the engine in the blink of an eye. No warning.

PaulM

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84 500 SEL (307,xxx miles)

Thank you Paul for the correction and support. I share this thread with my mechanic and he is in the process of following with the check points mentioned.
I should receive some feedback by tomorrow.

The part the still puzzles me, is the cold start valve not getting power. The OVP relay and the FPR have both been replaced and still intermittent power to the CSV at start up. This is why he designed the rocker swith to perform the function. Ideally I would like it to work as designed.

Thanks

Ron

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Ron, I don't know the exact temperature for your 560, but my 84 500 only uses the CSV when the engine water temperature is below 60 deg F. So this time of year, it won't be used at all, so no power will go to it. I don't think you have a CSV problem. The engine computer should take care of getting the correct amount of fuel to the engine.
I hope this helps.

PaulM

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84 500 SEL (307,xxx miles)

PaulM

I understand what you're saying and it makes complete sense. If not a CSV problem, what do you think ii may be related to?

Ron

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it sounds like you need a new mechanic. here's list of shops in richmond that speak mercedes-

Mercedes-Benz Repair Shops in Richmond, VA | Independent Mercedes-Benz Service in Richmond, VA | BenzShops.com

i can vouch for import ********. if none of these appeal to you, i strongly suggest eurotech in stafford. he's a ways out, up us 1, but worth the trip. rick came from the dealer in f/burg and has been in his place for a long time. good luck, chuck.

********

Thanks

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