ps2cho

Hi guys,

I made a thread over at the mercedesshop forum and it got to 4 pages long and now there is almost no responses so I decided to try here.

I will sum up the problem and everything we have done so you don't have to go through the entire thread.

Firstly, the car is a 1988 300TE with 65k miles on it when I bought it ($3000!) and it would stall randomly and misfire hard. Here are pictures of the spark plugs every 300-400 miles:



First we did a compression test and these were the results:
We next put 20/50 oil into the engine and it leaked less. (it was using a quart of oil every 500 miles)

Next we changed the duty cycle to 45-50% and replaced the OVP which fixed the stalling problem.

Then we replaced the Voltage Regulator.

Finally got round to doing the Valve Stem Seals at 72,000 on the car:




^ As you can see the engine is in amazing condition.

This solved the oil leaks onto the spark plugs and now it does not use a drop of oil at all through the 3000 miles before I get an oil change.

Next we replaced the Ignition Leads as they were certainly making less than stellar spark's with new Bosch leads which helped the misfire A LOT! It is STILL there though.

Lastly, we replaced the resistor style spark plugs with new Bosch NON-Resistor spark plugs like the car is supposed to have. I couldn't notice a difference in the misfires.


What is our next course of action to fix this horrible never ending problem?

The previous owners said they replaced the O2 sensor 6 months before we bought the car, but could it have gotten contaminated through the oil leaks we had?

What else could be the problem here?

Any help would be very appreciated!!!

Thanks, ps2cho

shdoug

Misfire?! I'm surprised it even runs with those plugs looking like that. What is getting into your combustion chamber to cause that much build-up in such a short time? Are you losing transmission fluid? Sometimes when the diaphragm in the modulator develops a small leak it can suck transmission fluid into the intake manifold and cause misfiring. I would think you would notice other symptoms if this were the case, but I would look for signs of this to be sure.

What kind of fuel are you using? It should be premium, never anything with methanol or ethanol. If you're not burning oil any more then the foreign chemical that is not burning completely it has to be coming from the fuel or the transmission, I would think.

Is that the correct spark plug? My source shows it should be H9DC. Yours say R6 591. Double check the part number. Too cold of a plug will cause build-up and then misfire.

Your engine looks great! Compression is good so it's probably something simple causing your problem.

If it's not ignition related, you may have a bad fuel injector. Have you determined which cylinder is misfiring, or is it kind of a random sputtering?

What about replacing the distributor cap and rotor? Are you sure the plug wires are in the correct order? Simple stuff, I know, but if you just put the wires back how they were, they might have been incorrect to begin with.

ps2cho

Sorry, forgot to clarify: Those were the spark plugs BEFORE we got the Valve Stem Seals done and with the resistor plugs. Yes I have the H9DC's right now and the plugs don't have a dab of oil on them at all now so the repair was a success!

Yes I am using Premium fuel and there is no transmission leak.

shdoug

Cool. Yes, I can see worn valve guide seals causing that build-up!

I would concentrate on the ignition system (check in the dark to make sure nothing is arching) and fuel injectors. How does the exhaust smell? Does it seem to be getting too much gas? That could be the K-Jet system out of adjustment.

The O2 sensor could have been fouled by the oil, but should not cause a misfire. It is not even used when the engine is cold.

ps2cho

I'm not too car savvy yet, my dad is the mechanic here I'm just trying to get some help when he's at work on the next step as he knows how to do the work...I just gotta try and help him find out what the problem is. We started very linear and fixed cheap easy possibilities as we could have spent alot more on other parts and not have it fixed.

As to the O2 sensor, you say it is not used when the car is cold....Well the car misfires right from first startup, so therefore I am assuming, as you said too, it can't be the problem here.

Are there anyways I can find out if the injectors are ok?

As for the misfire...I will have to find out which one's are doing it. I don't think its random sputtering...but I may be wrong.

ps2cho

Forgot to add, yes cap and rotor were replaced and I have double checked the plug's are in the right order. There is a diagram right above that has them shown and I just followed it exactly. I actually did it wrong once and it sounded really unhappy so I went back and corrected it and it was back to the regular shaking.

braknstuf

Somewhere in your engine bay , thier is a resistior that sets the retard make sure that this has not been tampered with - more info on this site just do a search.

Hows about that wiring harness, these often cause all sorts of wierd problems - may be worth taking a look at.

MAS - if you read back through the stuff on there you can see that the MAS can aslo cause some seemingly unrelated issues but sputtering is one of them, def worth a try.

I once had a subaru with hesistation and other wierd problems added a kit like this: http://cgi.ebay.com/ebaymotors/AMG-M...spagenameZWDVW
and made sure the ground points were not painted, helped things out alot - might be worth a shot for 25$. I highly doubt its an actuall AMG product but im pretty certian it functions all the same. Keep in mind you car uses a floating point ground and this can vary at diffrent locations througout the car - by adding a home run to the battery it levels ground around the car and provides consistent readings from sensors all over the place.

shdoug

The wiring harness was not an issue in 1988.

First determine which cylinder is not firing by removing the plug wires one at a time. The one that does not make a difference is the dead cylinder. You may want to do this with the engine off to avoid all possibility of getting shocked. Remove wire #1. Start engine. Rev it a little and see if it's worse. If yes, then plug it back in and move to cylinder 2 until you find it.

When you find it, remove that fule injector and swap it with another one from a different cylinder. See if the bad cylinder comes to life and the one you took the injector from is now dead. If so, you have a bad injector.

ps2cho

Thanks, I will try this tomorrow.

As for the resistor, I removed it myself as I heard it increases performance and gas mileage(it really did!) I tested with it in and out. It didn't seem to affect the misfires at all, but my freeway gas mileage went from 17.2 to 20.8 using the same conditions and same distance and speed (I wanted the test to be exactly the same). So the resistor isn't affecting the car. I had no pinging except when accelerating hard from 80mph+ with my foot to the floor which I never do, so that's fine. I read the huge thread over at mercedesshop forum about it and they said it depends on where you live and gas you get

As for changing the injectors, is it a difficult job? More or less difficult as compared to the replacement of our Valve Stem Seals? That took us about 5 hours total and was not too hard.

Also the previous owners said they replaced the injectors...but I will go ahead and do those tests so we can be sure they are still not damaged.

shdoug

Replacing the injectors looks easy. Here is the procedure.

ps2cho

Looks that I could even do this myself. I hope that an injector is faulty because I just want all of these problems to go away so I can drive what is otherwise an absolutely beautiful car to drive.

shdoug

^ That is a SWEET car! With the low miles and what you stole it for, I wouldn't be afraid to put whatever money is necessary into it.

ps2cho

Thanks Will post back tomorrow with the results of the injectors. What type of idling should I realistically be looking at? I don't want to be expecting an idle that is not realistic. How exactly should the car of my age idle when running right? Because I can feel the car shake and others can too when my car is idling or come to a stop on the road...so I want to get this fixed so it's less embarrassing when others are in the car with me

shdoug

Another thing that can cause a misfire at idle only is an intake manifold gasket leak. This can be tricky to find, and I don't think it is very common on the M103 engine. You could spray WD-40 around each intake tube where the gasket is and listen for a change in idle as you move to each cylinder.

Rough idle in general is common on this engine (common, not normal) but it should not have a regular misfire. Do a search on this forum and you will come up with a lot to read.

myfirstbenz

NICE TE! Same color as mine, I love the diamondblau.

ps2cho

Thanks! Is your grill black or is that just the picture? I painted my original Gray grill black and it does make a really large difference! Looks great!

I don't know if this helps, but the idle is not solid either. It fluctuates between 700-900rpm when in park. When the car is in drive and idling, the shaking is worse because the RPM's drop lower than they do in park. The engine sounds great when revved though. Power is very clean and it sounds so smooth...its just the idling problem. When I am driving you can't notice the misfires due to the movement.

And yes the research that I have done has concluded this is a common problem with the 124/M103. I just have to narrow it down to the problem with my one. I will search around this site and see what I can dig up.

braknstuf

Might check the motor mounts, when they get compressed thier pretty good at transfering engine vibrations.

ps2cho

It can't be the mounts because the misfires are inconsistent. If the mounts were the cause of the shaking, the car would shake the same amount each time I drive it, but it doesn't. Some days the misfires are worse and the car shakes more and other days it's almost unnoticeable(hardly ever though).

On the days when the car is not misfiring bad, the idle is great and the car is quiet and smooth...and other days its like riding on a bumpy road...but while not moving.

shadowgriffen

Def would look into injectors.

shadowgriffen

mine Idles at 550-600, and it's like butter

ps2cho

The thing is that the previous owners said they replaced the injectors...so I wouldn't think they could have done it wrong. Once I get home I will give it a test and we shall see what happens. Now, is there anything down the line that could cause it to show problems like it is the injectors, but in fact is something else? Kinda difficult to explain....As in something before the fuel injectors? If they were replaced by the owners, and it didn't fix it, is there a precursor to the injectors that could be faulty? I don't know much about cars (this is my first! but I am learning fast)

Also shadow: What year is your TE?

shadowgriffen

1988

ps2cho

When idling, can you feel the engine shaking at all? I understand that a car 19 years old is not going to idle as smooth as a brand new car, but I just want to rid of the car shudders.

About to pull each plug right now as I have the time. Will post back with the results.

EDIT: Results:

Each spark plug that I pulled separately made the misfires alot harder and each plug removed causes the same amount of harder misfires. Does this conclude that the injectors are not the problem here? As I said also, the previous owners said they had the injectors replaced.

What about leaky injector seals or are they covered under the test I just did?

Oh and what should be here? Something's missing. Is this where the idle control valve is supposed to be(cant remember what's supposed to be there)? Could the ICV be a possible problem
?


Last thing, we replaced the breather hoses too. So check that off the list.

shdoug

Now we're getting somewhere. Cross off injectors and ignition related issues. It sounds like a vacuum leak of some kind. I'm not sure what's missing in your pic, but that doesn't look like a vacuum hose to me so I don't think that's your problem. I would check injector seals next. Spray WD-40 around each injector while it's running and listen for a change. Look everywhere for a vacuum hose leak. There should be a diagram under the hood. Trace each line and look for cracks or disconnected hoses and tubes. Remember to check the transmission modulator and brake booster lines.

ps2cho

The seals were also done with the injectors, so I would assume they also must be good too. Do you still think I should check them? I will check for the cracks in the tubes. I have the day off work and school tomorrow so I can have a good hit at doing some tests.

And thanks for you so much for your help so far! This misfire is very frustrating and I cannot wait to have the car running nice. It hasn't been running nice for a long time.