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.

what exactly is a frozen piston? :confused:

One that won't move.

The thermostat (as are all thermostats) is a device that moves with temperature. In this case it moves the additional air slide piston first and secondly the piston transmits the movement to the internal linkage of the mixture governor.

Just a reminder - the 'thermostat' steve is referring to is the one on the fuel injection unit, not the cooling system thermostat you asked about earlier, which is in the housing at the rear end of the upper radiator hose.

Happy Motoring,
Mark

Just to clarify.....
 

So I have 2 thermostats.. 1 in the cooling system, and the other in my fuel injector pump.

Can both of these be causing me to run rich, or just the pump's injector. I can understand how the injector thermo could me causing me problems, but not how the coolant thermo can affect the fuel mixture.

What could cause a piston to freeze?

TIA

The thermo-sensor/thermostat on the fuel injection unit senses engine coolant temperatue to adjust the fuel mixture from rich(engine cold) to normal(engine warm). If the cooling system thermostat is stuck open and the engine always runs cold then, naturally, the thermo-sensor will tend to maintain a too rich condition.
Of course, the thermo-sensor on the injection itself or the 'piston' that it operates could be defective/stuck. There are other sensors, mechanisims and valves on these mechanical injections that can fail. Before you attempt repairs, find a detailed shop manual on this injection system to see what you might be getting into. Experimenting with gas and fuel systems can be hazardous. You might want to check out that Houston MB shop that Steve suggested.

Happy Motoring,
Mark

Yeh,man,if that shop Steve suggests has someone experienced in old Bosch mechanical injections,that's the way to go.There are adjustments on the pump,but you better know what you are doing.If,for example,you try to adjust the idle mixture with the engine running you'll lacerate your fingers and destroy the pump.There is a screw to adjust the main rack,but again if you aren't experienced,you can soon find yourself in quicksand.Also there are 2 white screws to adjust upper partial load and 2 black screws to adjust lower partial load,but you don't even want to go there.Find someone who understands these adjustments and he or she should be able to get the bugs out of your SL.Then you can put it on the road with the top down,listen to that beautiful exhaust note,and thank a professional mechanic for a job well done.
Good luck.
Peter

I seriously doubt my wallet will be thanking him!

But anyway, I'll give it one last shot this weekend. (figers crossed)

Every once and a while I feel the need to remind people that I make my living fixing cars.

I try really hard not to be offended by the public's horror at the cost of auto repair. I usually do not bother to point out that for a small diagnostic charge (usually under $200) the correct answer can be had without the real expensive process of parts substitution.

Other than the youngsters on this site I predict that my personal income is probably in the lower 25% of all that venture to this site. I can say that I love the challenge of fixing cars and I have been blessed to be able to say that I have spent my whole life doing exactly what I wanted to do.

I spend as much time talking with technicians as I do on this site and know them from all over the country and locally. I personally believe that as a group they are honest, hard working, free-spirited, individuals. If there is a weakness to the industry it is probably do to the level of training given to some pretty low paid technicians.

I can tell you that in my shop if we have failed to successfully solve a problem it probably has cost me more than the customer. While we all make our money hanging waterpumps and brake pads, diagnostics is both where the fun is and where the money isn't.

Steve - I know what you are saying - perhaps people get disgusted with ALL mechanics - because they have been taken to the cleaners or not been happy with the work done by untrained or unscrupulous mechanics. The good get tarred with the bad. I myself became a shadetree mechanic because where I live good mechanics are hard to find. My first bad scenario happened in 1990 when I took my Aerostar to a Ford dealer for a tuneup and got hit with a $200.00 labor bill to install a cap and rotor, air filter and 6 spark plugs. They said they had to jack the motor to do it. OK - I understand. The part I didn't like was after I drove it for a week, I popped the hood to check oil and found 3 bolts about 2 1/2" long sitting on the rad by the hood latch. When I asked them about it - they said "if it is running right -don't worry". I worried until I got rid of the van. Stupid thing that a pro should not have done. When I got my Mercedes I thought - the techs at the Dealership MUST be good. - I took my car there for a miss at idle - $400.00 later and one new spark plug wire - it still missed. The answer " it can't be- the computer says it is ok" When I showed them it wasn't - they said they had no idea. I was ticked off but decided to work on the car with my friend who does mercedes repairs as a hobby. When we started checking under the hood - the computer box was loose - they took out the nuts that held it in place and forgot to replace them. I now maintain 4 VW's, my Mercedes and an Olds. My daughter just took her VW with battery problems back to the repair center that sold the battery to me to check the battery - $20 later the guy said there was nothing wrong with it. I learned about checking batteries on the net and found out one cell was shorted. When we took back the battery with this info they replaced it under warranty but would not refund her $20.00(oh yes it was the problem). I know all this sounds like puny nit picking -BUT - when I am expected to pay premium dollar for professional diagnosis and repair and I get sloppy work and poor attitude in exchange - I decided to do my own repairs as my standards seem higher than theirs. As many threads show on this site others have had bad mechanic experiences. It is truly unfortunate that quality shops and techs like yourself suffer because of some shoddy shops out there. I guess it is just human nature to classify all the industry the same. You ever notice on this site how people always ask for a quality shop in their area??? When the choice is aggrevation or do it yourself, I choose do it yourself. Yes I have spent money needlessly for parts - but I wrote it off to education.Too bad cars were not small enough to send in the mail - I'd rather have an honest pro like you do the work than me. If your shop does quality work and your mechanics are pros - you will always be busy - a running car is not the goal - Customer Satisfation is. It is also the best advertising. Sure you will get the deadbeats that will try to get things for nothing from you - but I bet they are in the minority. Most people (especially those who own Mercedes) don't mind paying if they get what they paid for.

I fully second the comments in the previous post. Steve, going thru this thread makes me pretty confident that you are one of the best out there, technically as well as professionally. You are providing your expertise free of charge on this forum, and that is something that we all truly appreciate. And as has been said earlier, man if I was within a few hundred miles of your shop, I would never go to any other mechanic.

But the unfortunate reality is that in my 11 years of experience in maintaining a mercedes, unfortunately, 75% of the shops/mechanics I have come across have been either incompetent, or unscrupulous, or both. And this is when 50% of them have been at authorized mercedes dealers, in 3 different cities. I can give you tons of examples of authorized dealer technicians giving WRONG advice, just to make money. To top it off, more often they have not had a clue as to what the problem was. This problem is exacerbated by the individual called "service advisor" at these dealers. He is probably a used car salesman, who behaves like a salesman, not like a tech, had zero knowledge, and will say any crap just to make money. I guess that's his job. And he is the one you have to deal with, or through. You won't believe the kind of quotes I have obtained, and the unnecessary repairs that have been suggested, or the "diagnostic" charges that have been levied without any result. I had a rough idle at cold, and 1500 dollars later, it was solved when the oxygen sensor was found totally dead. Shouldn't the tech have noticed it the first time he tried to adjust the fuel mixture - the output was constant. and I can go on and on. Believe me, since you are a tech, you probably haven't experienced the frustration of a person who doesn't know too much about cars, being taken for a ride again and again and again, by people who you would think one could trust - the authorized dealers and independent MB specialist. There is only one, I repeat, one one guy I found to be both honest and competent (he is in Queens, NY). Anyone else I went to, first asked me to shell out at least a grand.

So that's the reality out there. Again, Steve, its all the more commendable, and a relief, to see people like you around. Maybe you should branch out, set up shops all over the country, and get these bad guys out of business. I will personally make sure everyone I know comes to you for repairs.

Rad-man

Listen to Steve-he has been helping me with my rich mixture-see the related posts on this Vintage section of the board.

To re-emphasize, the thermostat is the FI thermostat which is the vertical housing on the back of the pump with two hose connections. I ordered a new thermostat (PN 001 203 95 75), figuring that after 30 years, I would give the old thermo a rest.

Also see Steve's response re: what to check first regarding rich mixture before adjusting the pump.

regards,

thanks for the post. It's a bit of a relief when people have some of the same problems as I do. (in a good way).

Re: Fouled plugs
 

I put my finger over the hole and the engine died!! (I'm happy because I'm hoping I finally found the culprit to my problems).

I took off the filter and started the engine up. I immediately heard air being sucked into the engine. I left the car on for a good 20 minutes and it would stall if I put my finger over the hole.

Is there a difference b/c the Bosch or the Berh? Hopefully this 40$ part will fix all my probs. thanks a lot, guys!

Just so I understand, the thermo should open when the engine is cold, and then close when the temp reaches operating temp?
Why exactly does it die with my finger over the hole? Shouldn't this simulate the thermostat closing? So why would the engine die with the thermo closed?

Because your idle speed has been adjusted to compensate for the fact that you are always running with the same amount of additional air. After you replace the t-stat you will have to adjust the idle air screw as it won't run when the car warms up as you have surmised. Remember engine speed is determined by air not fuel! To raise engine speed air must be added.

BTW the t-stat does not open or close it just gets longer as it warms and shorter when it cools. This action moves the piston below the t-stat which is the air slide. REMEMBER it may not be the t-stats fault. If the air slide piston is frozen open a new one will not fix it. I would verify the movement before replacing. I would replace though as I think the t-stat will not be very good after trying to push a frozen piston for a while. It is very likely that it will be frozen as no movement usually leads to such. (or is such).

The piston is in the housing below the t-stat cylinder. They are easily cleaned/freed up. Drain your coolant and pull the t-stat housing (cylinder) - two screws. With the t-stat removed push on the piston where the t-stat plunger sat. It should be spring loaded up. It should easily push down and spring back. If not remove the other two screws and take the housing to the bench to free up. NOTE: there are shims beneath the t-stat and beneath the housing. Besure to replace them as they were.

so pretty much this is where the cause of my rich mixture lies?

After 30 years, the thermo and piston have stopped working properly, and to fix these I need to clean the piston and replace the thermo?

I guess this was my cars way of teling me it wanted a new distributor, wireset, and plugs. oh well

a quick fix?
 

I just ordered a new bosch thermo from Fastlane, but will whis work until I get the part...

What if i clog up the threaded hold, and adjust the idle screw so that it wont die. Will this simulate the thermo closing (or getting longer), and even out my mixture?

NO! You are missing the point. The very simple test of the airflow allows one to make decisions about where the mixture problem comes from. It is cheating so to speak. It only tells us something because of the relationship between the mixture mechanism and the air mechanism. Screwing with the airflow will only change the engine speed.

280SL
 

Rad-Man.
We professionals don't mind helping a week-end mechanic, who has mechanical abilities,with some problem.For some guys,tinkering with their cars is relaxing and provides a sense of accomplishment.You on the other hand do not even have a clue.I can't believe we have spent as much time on you as we we have.I have 3 of the SLs like yours,and they are expensive toys.Now quit being so CHEAP and take it in.I've already given you all the clues on how to find the right person;reread my earlier posts.There is a limited number of professional mechanics on this site,and it is unfair of you to monopolize their time trying to get your car running for FREE.Others appreciate the help.I will be glad to answer tech questions for you in the future,since I know that car from end to end,but only after you've taken it in and got it running.
Good luck,
Peter

autozen,
I really appreciate all the help you guys have given me, but you need to cool down. I'm 22 years old and this car was my dad's baby. Now it's mine and I want to get her running again. I do ALL mechanical work on my jeep, but I guess I'm being extra careful with this thing. I'm sorry if you feel like you have wasted time on me.
I'm paying for college, and trying to maintain 3 cars. I really cant afford taking this car into a shop right now........

ANyway, I just got my new FI thermo. (# 1 287 230 002)
I'm hoping this will finally fix the stupid mixture problem. If it dosent, I wont ever post here again.


as for the install, stevebfl gave me a pretty good idea of what i need to do: "They are easily cleaned/freed up. Drain your coolant and pull the t-stat housing (cylinder) - two screws. With the t-stat removed push on the piston where the t-stat plunger sat. It should be spring loaded up. It should easily push down and spring back. If not remove the other two screws and take the housing to the bench to free up. "

anything else i should know?
I'll let you know how it goes. Peace

Fouled plugs
 

Rad Man;
The cold start valves were famous for leaking into the intake manifold.
The valve is located on the far right side of the intake manifold,it has an elect. solenoid ,and a fuel line to it.
On the valve assy. find and remove the 7mm screw,have someone turn on the ignition but don't crank,if gas comes out of the screw hole then the valve is bad!
M.F.

Rad,

Don't let one person giving you a little lip ruin your experience here.

You may not get the problem resolved right away, but you will get it resolved.

Don't think that people here wont help you, because they will, sometimes its best to post and wait for a response for a few days, then check back and see what you have gotten.

We would hate to see you leave our community because you and one other person had a disagreement.

Alon

sorry this is so long...
 

After pulling off the housing and taking it apart, I've gotten a better idea of how this thing is supposed to work. I noticed how when the piston is all the way down the threaded hole (where the little filter attaches) closes and stops air from being sucked in. This explained why you guys asked me to check it at operating temp...
After putting in the new thermo, the amount of air being sucked in droped considerably after the engine warmed up, but it never stopped. After 15 mins of driving around, the engine would still die if I put my finger over the hole.



I know I said I would try not to waste any more of your time, but I feel soo close to fixing the thing.

Here is a pic:
http://www3.baylor.edu/~Amir_Radfar/fi.jpg

I'm pretty sure my engine has been replaced with an SE engine (supposedly a direct replacement), but I can't help think that someone before me knew there was a problem around here and tried to rig something up.


If you look at the pic, you can see 2 brass-colored rings. The one on the left is part of the thermo, and the right (thicker one) is some kind of washer. Is this the normal setup? Call my dumb (oh wait, some of you already have ;) ) but is this the way is should be?

I'm thinking that since the amount of air being sucked in actually changed from a lot (I left the little filter off, and the sucking was LOUD) to less... the thermo is actually moving in there. But I'm thinking that either that little 1/4" washer is stopping it from extending all the way down or the thermo just isnt strng enough to push all the way??

I guess thats about it. I think I'm going to put the old thermo abck in to see if it does the same thing. Maybe the piston just needed to be freed up.

Thanks in advance...

If you have it moving and have a new t-stat you are almost there. I think the pieces in the picture are right. The t-stat does need a place to seal against and the piece below it is beveled to accept the roundish shape of its bottom. Since you are now experienced at getting this apart and back together, you need to try some adjustments.

As I was saying before the relationship between the airflow and the mixture control is such that when you get the airflow right you will have this area of mixture control within tolerances most likely. Let me point out that when the airflow is right it will still suck your finger in but it will not drop engine rpm by more than 50. I personally like to get it to nothing as these systems are often rich for more than one reason. Also beware that almost evry time I fix one of these so simple problems, someone has already messed with all the other adjustments (which absolutely should not be messed with till the temp mixture correction has been corrected.

With all that said lets shut off the airflow. You have noticed that to finish closing off the airslide you need a longer t-stat. Well make it longer. Add small washers to the area where the end of the t-stat sits. Start small as we do not want to go to far. Remember that when its all done you are going to have to open the airscrew as it will not idle high enough when the add air is properly shut off as you realized. The most important point with this additional air/cold enrichment adjustment is getting the warm setting right as this is where the car is mostly driven and is almost always the cause of way rich mixtures.

I think thats the cold start valve. Take the fuel line off and plug it too be sure it is not leaking.

You may have gone too far with the t-stat. It was probably so loaded up that it took a while to appear lean. Just a thought since you got this down now.

While you are eliminating other things (cold start valve leaks) disconnect all the electrical to solenoids on the rear, I have seen the starting enrichment solenoid be hooked up improperly and throw the rack rich. When warm none of the solenoids are necessary for proper running.

good news............... and some bad
 

Well, I finally added enough spacing, and the piston gets pushed all the way down at operating temp. There is no air being sucked in, and the engine is not affected when I put my finger over the hole.
Then I took out the plugs and cleaned them with some gasoline and an old toothbrush, and after putting everything back together, the engine was running wonderfully!

After 10 mins of idleing in the garage and another 15 mins of driving around, she started acting up again. The engine started sputtering and would try to cut off under high acceleration.

I took one of the plugs out when I finally made it home, and it was BLACK! DagGUM carbon fouling!

One thing I noticed... Before I had the theromo working correctly, a lot of black residue would be shot out of the exhaust pipe (a clear sign of rich mixture, as I have been told), but now there is none.

Whatever the problem still is, I know the FI thermo was a big part of it. Thanks to all who have helped me eliminate one of the culprits.

Re: Fouled plugs
 

Ok, I just unscrewed the little 7mm screw and turned the key to the on position. I could hear the fuel pump working (I let it run for a good 3 minutes), but I never had any gas come out.

whew.

One thing I thought of... a few months ago I put a bottle of STP fuel injection cleaner in the gastank. I figured that she had been sitting for a while, and needed a little cleaning. Could my problem be in the gas itself?