1990 300SL m103 refuse to start

Hi all,

Last week my 300SL engine sound like it is running on 3 cylinders so I send it to the workshop. They checked the sparkplug and discovered that the no.6 sparkplug is dead and exchange it. When I wanted to pick the car, the engine started ok then developed the same sympton and then it went dead. The enfine refuse to start and it sound like there is no compression.
Do I need an overhaul? Any advise or experience is appreciated.

Regards,

[elau]

I don't think you need an overhaul on the engine yet. How many miles do you have on the engine? What did the mechanic say when you went pick up the car besides #6 plug was dead? Did he do anything else? It seems like the first order of thing is to find a knowledgeable mechanic to work on your car.

I am not a mechanic and not pretending to be one, but you may want to start looking for the obvious first if you have not done so. I will make sure all the plug wire are good, replace them all if they have been in the car for a long time. Check and replace any ignition related items if they are in the car long time. Check your OVP relay while you at it. Check your fuel filter and replace if needed.

Remember, your car is about ten years old and some of the items I mentioned may need replacement.

Do a search in the forum and you may come up with more ideas. Good luck.

Hi,

The mileage on the car is about 30K miles. I seldom use the car and before this problem developed I have not use it for the last 3 months. The no.6 plug seem to be oily when the mechanic removed it. I have heard about the OVP in relation to starting problem. How do I locate the OVP? The mechanic is a Mercedes mechanic but I having my doubt as well. Just don't want to be spending for nothing.

Thank you on the response.

Regards,

[elau]

I cannot say for sure for your model year, but I think the OVP is located just in front of the firewall on the passenger side.

If your car has been sitting, I will suspect your fuel filter. Dirt may have settled and clogged your filter and hence rough running. You may start there first.

Next I will suspect moisture in your fuel. How much gas did you have in the tank prior to starting your car? If your car has been sitting that long, moisture may have build up in your fuel line. Just a guess.

If your engine has only 30K, overhaul will not even be considered. You have practically a new car. It is probably some minor maintenance items you have over looked.

Hi,

Yesterday we did a compression test on the engine. 3 cylinder is not having good compression. It seem theya have to open it up to check the valve and the rings. Sigh ....
I will let you know the status as they will only carry out the work 1st week of Jan as they are pretty busy now. Is there anything else I could do ?

Regards

[maheath]

I find it hard to believe that an engine with 30k miles needs a bottom end rebuild. Is it using oil? My first suspicion would be that the valve stem seals need to be replaced. Used so little could dry out the valve stem seals faster. I don't see that keeping the engine from starting. I think you've got more than one problem. It's much more likely that the valve stem seals are fouling your plugs than the rings.

I'm with elau on going through the ignition components. If the plug wires are original, replace them. Also replace the plugs (copper, not platinum), rotor and distributor cap. Those are all common failure items and will run you a little over $200 for the parts. I replaced all of those on my M103 engine a couple of weeks ago. Very simple job. Randy Steele puts together a nice package that includes the suppressor cover and wire guides too. He's got one currently on auction here. Rusty Cullens at *************** will probably match his price.

The fuel filter is another maintenance item worth replacing, but I'd do the above stuff first to see if that fixes (or changes) the problem.

Hi,

Just curious. If the valve is faulty , will that contribute to the compression problem? We have check the spark and there seem to be spark and the fuel pump seem to be working. Maybe I will ask the mechanic to hold on first and run another diagnose.

Regards,
Zaini

[maheath]

Yes, faulty valves will showup on a compression test. You need to do a leakdown test to isolate the problem between the valves and the rings.

Hi All,

Thanks to all who responded to my problem. It turn out to be the ignition coil. So far the car is running fine.

Once more thank you.

Kind regards,
Zaini

[elau]

Glad you found the problem, and it is a minor one for that matter!! Now, take the car out and drive till your heart contents