How long has that cap/rotor combo been on the car?
Ignition wires... 7 or 8mm... from where? Proper routing (presumed)?

The cap/rotor show signs of normal wear. unless you SEE arcing from some location on the cap (inside/outside) to some ground point/other lead it is NOT abnormal.

I would suspect inferior ignition wires being affected by heat with the resulting corona/arcing to the most convenient grounds... one reason to ensure that the coil lead is NOWHERE CLOSE to metal... (I have mine secured to the radiator hose).
They went from 8mm wires to a less-expensive 7 some time back when I wasn't looking... in fact I recently had corona/arcing from a 6mo old set of wires... I had them replace them.

... my 2cts.

 

I suspect moisture is getting into the dist. cap & rotor area due to a worn out orange disc seal & rubber o-ring. Then again, it hardly ever rains in Ireland. . . . Just kidding. No rain, no beer right???

This would be a ideal time to R&R the timing cover seal and replace the metal rotor arm with the updated parts.

Be sure to use new genuine MB/Bosch/Beru parts.

see link
PeachPartsWiki: How to reseal the front top timing cover

 

Hi,

The cap & rotor were replaced 5 months ago but the car has only been on the road for the last two weeks & covered 250ish miles. It has been cleaned about a week ago also. so needs it every 100miles to cure the misfiring. Is that really normal wear for 100 miles? Also if that is normal then why does cleaning it make the car run perfect again?

I measured the leads with A caliper just now- 7mm aftermarket. However I do not believe the leads to be the issue here. I say this because the original leads arced, the new wires fitted to the original plug ends also arced (Which is how my local MB dealer does it anyway) & the complete new leads are also arcing slightly too. I think they didn't arc just as bad as the others simply because when fitting them I had cleaned the cap & arm too & fitted the new coil. Besides all these leads were 7mm anyway.

The King lead is routed away from even the water hose as when running it could actually create a continuous arc to the water hose!!! This was with the first two sets of leads. I never seen that before. Since carefully re routed there are no issues like that now with the king lead. I paid particular attention to the fuel lines!

I think the leads arcing & the cap excess wear are symptoms of the over voltage or increased secondary ignition resistance the car seems to have. I have checked & cleaned all earth straps too but this didn't help either.

I would like to see if I can get a refund on the Bremi cap & arm. I will measure it with very carefully with digital calipers before sending off then compare the readings with the Bosch items I will try next. perhaps a slight difference in the cap or arm is what is causing these issues?

sbaert; I did think about the O ring too. That link seems to be a M103, does the updated metal arm apply to the M104 as well? If there are any updated parts I will purchase from MB monday morning. With regards the moisture the car is locked in the garage all the time but I suppose moisture could still make its way past the O ring then stay in there

Could ignition timing or fueling problem cause issues like this?

Thanks for your help!

 

Be aware that the original leads (wires) have built in resistors that almost all aftermarket wires lack.

Therefore, you must use the original style leads (such as from Bosch or Beru) along with NON-resistor copper core plugs only.

Using resistor plugs w/ non-resistor leads will cause you grief. These engines detest any type of high-tech plug such as platinum, iridium, etc. Just plain non-resistor solid copper core as was designed by the factory.

Your early style M104 still has a cap & rotor and therefore the same applies as the link I sent for the M103. I don't know if the early M104 used the arm, but since you have a cap & rotor I'd venture to say you likely do.

When it comes to ignition parts on a M104, stick with genuine MB or Bosch exclusively. Also be aware that the ignition system on this engine was designed to be disposable, needing complete replacement every 100K with plugs every 50K.

 

The new leads are good quality & are exactly the same as the originals. They have the 1k resistors built in & I use the resistor less NGK BCP 5ES Plugs gapped at 0.8mm

 

Bremi is not OE for W124.

Suggest you replace cap, rotor & coil with new genuine MB or Bosch and report back. Ditto on replacing the orange disc & seal.

 

I couldn't agree more. I fitted Bremi cap and rotor to my 104.980 and the rotor died within 18 months. I replaced it with the original 17 year old MB rotor and things were fine again.

The car now has NGK non-resistor plugs, Beru leads and MB original cap and rotor.

To my mind, the 104.980 is a great engine that gives real fun with its 7000 revs but it MUST have 1st class ignition parts. My son uses mine from time to time and, judging by the rear tyre wear, he gives it a good sound caning. He always reports no-misfires.

So, in your shoes, I'd make sure that the best plugs, leads, rotor and cap were installed and take it from there.

The very best of luck to you.

RayH

PS: I note your concerns about moisture. My 300CE lives outside ALL the time. This is 1000 feet up in the Dordogne hills and rain, frost, sun and tempest all feature in the climate. A robust ignition system rebuffs all this and the car (its battery goes flat) was jump started in March, having been neglected since Christmas, settled into a smooth idle and then performed faultlessly. So, if funds permit, ditch that Bremi stuff and replace with MB. I know I have!

 

Well... ANY corona (glowing)/arcing that is VISIBLE to the eye at night IS LOSING POWER that is supposed to go to the plug.
Period.
Come to think of it... I see no seal in the edge of the cap. There SHOULD be one and that may be part of the cap issue... but Ive also seen worse looking specimens that did not adversely affect the performance.

oh well.

You say the DEALER replaced the wires but not the plug connectors? Interesting...

 

Ok guys thanks for your help. Everyone has their fingers firmly pointed at the Bremi Cap & Rotor Arm so I will order up replacement Bosch items pronto & begin the fight with my supplier to have a refund on the bremi items!

The reason why I didn't get mercedes items were the prices. They quoted me an eye watering £475 ($650ish) for the cap, arm & leads they were going to make. What they do is order up the little brass connectors that crimp onto the silicone lead & screw into your original connectors + charge you per M of cable. Bizarre but 100% true! This was supply only price.

However I have since found new genuine bosch items (cap & arm) for £129 all in! I paid more than that for the Bremi items.

With regards the orange disc I went out to remove it this morning. My T30 Bit sheared off in the bolt but I was able to retrieve the little stuck end easily enough. So rather than risk shearing the bolt off inside the camshaft I have thoroughly cleaned it up & it is looking good now.

The O Ring Seal was intact but a little hardened so I will order it up in the morning too.

Hopefully the car doesn't just spark up the new cap & arm also. It did destroy the original cap & arm but they were dated 1989 so I put that down to simply worn out, Lets hope I was correct!

I will keep you updated as to how the cars runs once all the parts are fitted up again.

Yes the M104 engines are great, 7000 revs & it loves it! Anyone that I take for a 'Stage' in the car are always very impressed & compare it's performance to a Porsche!

Just have to be very careful when overtaking in the wet it can be a bit of a handful! In the wrong hands it could get someone into big trouble very fast. Which is why I never let anyone else drive it

 

Just have to be very careful when overtaking in the wet it can be a bit of a handful! In the wrong hands it could get someone into big trouble very fast. Which is why I never let anyone else drive it

I learned this the hard way...tried to pass a slow car on the highway and didn't pay attention to the transmission mode. It was in S and downshifted. Did a 360 and almost hit both sides of the highway. :crybaby2: Didn't hit anything or anyone, thankfully.

 

I think it's fixed!

The lovely new Bosch rotor arm & cap arrived in the post today. I wasted no time in fitting them when I got home from work. But before I fitted the Bosch cap I compared it to both the original item & the offending Bremi Item.

The new bosch part is IDENTICAL to the original merc item in every way. No point in paying the more than double mercedes dealer prices then me thinks. When comparing the Bremi Cap & the new bosch the difference is Night & day. Take a look at the pic below

The Bremi item seems to have some sort of crap tin metal used as terminals whereas the bosch has nice shiny Brass terminals. Also even the way the terminals are cut is different the bosch having much beefier & better supported terminals.

Whilst waiting for the new parts I took all the old plugs out to asses their color & also to carry out a compression test on the engine. All was good but with the old plugs out it seemed rude to put them back in so I also fitted new NGK Items. Just to be sure to bne sure as we say here!

So it currently has the (good) aftermarket leads, NGK plugs, Bosch Rotor arm & Bosch Dizzy cap fitted. I took the car for a 40mile run and also run it with all the covers off the leads in my Garage with the lights out. Zero arcing evident anywhere in the system and the car is running great again, No misfiring at all & smooth steady idle

It also looks like euro car parts is going to give me a very hard time returning the Bremi parts (6 months old + 200 mile covered) but at this stage I am just glad the car is running good again. Hopefully this lasts & it doesn't decide to eat this cap too eventually

As for Bremi parts - Never again. I guess the old girl decided to educate me on this one

 

Hi,

what is your take on Beru parts for cap and arm?

 

as good or maybe better than bosch these days

 

Hi, sbeart already mentioned in this thread that Beru is an OE supplier to MB.

Personally I would only ever fit Bosch parts or MB now. Euro car parts never did refund the Bremi cap so it was a very expensive mistake. Never again.

 

I agree with your preference for the Bosch cap & rotor, JC220.
Also Beru, which sbaert mentions, seems to be okay. At least friends of mine who use them don’t seem to have a problem with them.

This may be a good oportunity, to let you guys know about some general information, which a Bosch insider made me aware of:
High ambient air moisture is usually never a problem for the ignition distributor. Although there is this O-ring installed in the distributor, it’s never airtight! On the contrary – It should never be airtight!
The O-ring is supposed to protect the distributor from splashing liquids and dirt.
Why should the distributor never be airtight?
The sparks between the distributor arm and the poles in the cap would cause the O2 of the trapped air to develop into O3 (ozone), which is a strong oxidant and would corrode the copper components quickly. That’s why the Bosch cap for instance has 3 ventilation ducts (you can see one and a half of them in the picture of post # 11)

 

HI. I know this is an ancient thread, but the key part to replace when replacing the cap and rotor is that insulative spark suppressing cap/cover that's behind the rotor. It's where most of your issues are likely coming from. I'm posting this because some people still rely on these old threads for their information. The cap/cover might look fine, but they degrade on a molecular level and allow arcing to the block. This part is almost exclusively available at the dealer and costs a fortune considering it's a plastic disc.

 

Yes that's correct- the insulating discs do degrade I know that now. This car has been stored mostly since this thread but it doesn't appear to suffer the ignition symptoms any more. If it does go back to that I'll renew the disc.

Bosch makes the insulating discs in their own packaging. Finding the correct Bosch x-ref is how to find them that way. Then search fleabay for a new Bosch item- cheaper than a MB dealer.

 

The M103 distributor insulating disc, Mercedes PN 1031580088 is, I believe, Bosch PN 1 230 500 176

googling suggests they are $100 parts. many vendors seem to think the generic bosch PN is NLA.

 

Good read up on this post .Waiting for follow up...

 

Hi everyone;

I have been having ignition problems with this car for quite a few years now. I have owned this car for ten years but it has been off the road for around 9 years as I have just finished restoring the car

The engine is the M104 980 early variant with the distributor cap & leads. The engine has 106K Miles on it & is in very good fettle. It had a full stripdown & rebuild as part of the restoration. All it ended up needing was new valve guides & valve seats relapped along with water pump & timing chains etc as a matter of course. The car was started regularly during its lay up & let idle to warm up until warm idle,the car wasn't back on the road until just a couple of weeks ago now!


So the problem is the car seems to have too much spark. The dizzy cap & arm get scorched up within about 100 miles of running along with arcing of the leads gradually getting worse & worse until a steady misfire can be felt at idle & heard from the exhaust. Once the arm & cap are cleaned & put back the car runs great again then the cycle starts again...

So far I have replaced;

Dizzy cap & arm with Bremi items (200 miles ago)

Ignition leads (twice- one with genuine good used & now with new aftermarket) Arcing visable with all sets but much less so with the new items but the coil was replaced at the same time as the new leads so not sure if that helped them too.

Spark plugs twice both times with correct resistor-less items (NGK)

Ignition coil (100 mile ago) new bremi item

Today the car started misfiring again so I took the cap off. The same arcing as always is evident & If I clean & refit it will run great again for a week or two. The cap & arm are still under warranty so I could have them replaced but not sure if this will actually help

I have attached a picture of the engine, the cap with it's arcing marks & the rotor arm as installed

Has anyone experienced issues like these before? What else could cause these problems? :crybaby2:

hi..I have the same problem and in fact more serious. Changed distributor cap and rotor to Bremi. Car starts and runs fine. Just 50km, the car stops suddenly and no ignition supply to the rotor. Changed back to old Bosch ones and the engine roars again. I suspect the rotor arm have some manufacturing defect. M104.980 24v.

 

I too had a sudden death issue with a 6 month old Bremi rotor and arm. Put back the original, 19 year old MB parts having cleaned them up and no more problem with mis-firing. Bremi rubbish binned in favour of costly MB ori

I have had EZL death problems in the last year that I discuss elsewhere.

RayH