Ignition problems... Why has my engine fouled 3 different sets of plugs!
 

Sorry for cross-posting, but I'm desperate!

I've replaced the distributor, rotor, cap, wires, and plugs (3 different sets of plugs!!!)

First set was a Bosch super copper core (not the W7DC)..
they were carbon fouled in a matter of months. It took me a while to figure out that they were actually fouled b/c I didn't think they could have been the source of my problems.

The second set was Bosch PLATINUM... they fouled in a matter of 2 days.

So the other day I ordered the wires and W7DCs (copper core)... The car was running better than any of the other plugs...
But then they fouled after about an hour.

What the hell is going on? The only ignition part I haven't replaced is the coil. I figure if it sparks that means its fine.

Any help would be appreciated. TIA

Sounds like it is running very rich if they are carbon fouled or possibly burning oil.

how do I fix that?

It is fairly rare that ignition components cause spark plugs to foul. It can happen of course, but usually fouled spark plugs are due to the burning conditions in the combustion chamber.

Fouling is caused by an engine burning oil, or one with a very rich mixture. In the case of burning oil, you would probably see the oil level go down steadily, and get some blue oil smoke out the back. In the case of rich fuel it would tend to run funny (perhaps) and might throw black smoke out the back. And it can be a combination of these two problems.

One of the cheapest solutions for a rich fuel mixture is that your air filter is blocked.

Tell us which vehicle this is, what kind of oil you have in it, and how much mileage is on the vehicle.

Ken300D

well... I THINK its a 1970 (ish) 280 SL with a SE engine in it(I'm waiting on a Build Sheet from Germany). Who knows how many miles are on it. the odometer reads 36,000 km

I replaced the air filter recently, so I guess i can check for any clogs or anything.

I don't sound like I'm buring oil, but the car shoots out black smoke and a lot of black residue under high RPMs..

I know the injector pump can be adjusted, but I also know I shouldnt touch it! :)

Hmmmm. Well, OK. One thing that comes to mind is to get the right plugs for the engine. Different engines use different spark plugs. In fact, they can have different lengths that can cause severe problems if you put a long spark plug in an engine that requires a short one - the piston will contact the spark plug.

The other issue is the correct heat range of the spark plug. The same size spark plug comes in different heat ranges, typically to match the burning conditions in the cylinders based on things like compression ratio.

So, make sure you get the spark plugs not for a 280SL, but for the engine you have in there.

With the black smoke and black residue, you must be running rich on the fuel.

Is this a new-to-you car? Or is this a situation that has just started to happen with a car that has run well for a long time up to this point?

Ken300D

I have an SE engine, but I have been told that the SE was pretty much a direct replacement for the SL. I ordered my wires and plugs off this site (fastlane). They are Bosch W7DC plugs.

Fastlane shows these to be the right plugs for the SL and SE (I went ahead and ordered the ones on the SE page).

The car has been in the family for a number of years, and my father told me there used to be some kind of booster on the coil. He doesn't remember what it was exactly, but he said that the thing burned up and the car was never been the same since.

Maybe the previous owners knew it was running really rich and had the booster added on. I guess that would make sense. What exactly does a booster do? Up the voltage and make a bigger spark?

How do I go about evening out the mixture?

All you've said indicates a way too rich fuel injection problem. These SL mechanical fuel injections do have mixture adjustment screws, however, they also have a coolant temperature sensor and an air temperature sensor which can malfunction. Also, if your coolant thermostat is stuck open and causing your engine to run cold it may cause the injection to run rich. These or other factors can cause a too-rich mixture and plug fouling. It may be time to check out the 'Good MB Shops' section on this forum for a reliable Mercedes repair shop in your area. At the very least, I wouldn't make any injection adjustments without checking a comprehensive shop manual for this fuel system.

Happy Motoring,
Mark

" ...some sort of booster for the coil ..." This makes me think that there was an added electronic ignition unit, like a CD unit. I know that Delta and PermaTune were very popular in the 70's to help keep the plugs clean on German cars. I have and still use one. Often the primary coil wiring is changed. If you can get close to the coil and see if only the factory wiring is connected. Look for any modifications to this wiring. Ideally, get a copy of the factory electrical diagram for the engine to confirm.

Additionally have you tested the coil? Is it good?

I had this problem in my '65 911. Just couldn't figure what the (&*^%&%*#$ was going on. A friend suggested changing the coil. Suddenly all the problems went away.

My 2 cents.

Jeff

which thermostat?
 

I was looking on FastLane and they sell the following thermostats. Which one do I want?

79 degree
87 degree
71 degree


TIA

If you're sure that your SL is running too cold all the time -
71 C = 159.8 F
79 C = 174.2 F
87 C = 188.6 F
I don't have the Mercedes factory engine manual for the 280SE/SL but my 'Haynes' Mercedes 280S/SE/SL manual specifies an 87 C thermostat. I'm running a 79 C in my '72 250 (2.8 - M130 engine) but it's carbureted. Unless your SL has hot running problems in summer, I'd go with the 87 C.

Happy Motoring,
Mark

thanks AGAIN :)

Fouled plugs
 

Rad-Man,
I still recommend NGK, but you shouldn't be having any problem with any brand.Mark's thermostat is a good one,andyour engine takes a 79 deg thermostat. You also have a thermostat on top of the inj pump. When the engine is cold it allows extra fuel and air.Unscrew the little filter thingie off the back side of the pump,I think it takes a thin 22mm.It has been so long since I've worked on any M130 engines that I can't remember.With the engine at full operating temp put your finger over the threaded hole.There should be no change in the engine.If your finger gets sucked in and the engine dies this special thermostat needs to be replaced.Notice I said SPECIAL,and we all know what SPECIAL MB parts cost.Also put the little filter thingie to your mouth and blow through it.If your cheeks puff like a tuba player,it's plugged and the car will run extremely rich.Also the cold start valve on the intake manifold could be dripping.Bottom line;Mark is right on.Find a good shop in your area that knows vintage MB's.If you go to a shop that is loaded with scanners and techs under 30,you're in trouble.You need a facility that has an old fa*t like me hanging around.
Good luck,
Peter

haha- thanks for the advice. I will check all the mentioned things this weekend. Then I may go ahead and replace the coil just to be able to say I have a new ignition system.

I've looked through the " Good MB shops" section on this forum, but I didnt see anything in Houston. On top of that, it is going to be hard to let someone else work on one of my cars :rolleyes:

Listen closely to Peter's advice. It is almost a certainty that you have either an inj pump thermostat problem or a frozen piston (that it works against).

Do the test that he describes and you will find your problem.

If that doesn't solve the problem I would recommend MPH Automotive in Houston.