FYI Essential M119 Ignition "Tune Up" mods [Distributor cap vent / slot]

[JC220]

Well I didn't need to wait long for an update! Within about 75 miles of driving, there is already oil residue at both electrical connectors. I had disassembled these, degreased the wires & metal female sockets, and replaced the plastic pin bushing housing (connector). And, the solenoid male connectors were bone dry when installed. I cleaned everything again, this time adding a small paper towel diaper below the connector.

I believe the magnet inside is not as "sealed" as people think it is. Somehow, oil is getting inside that and leaking out the connector. It may require heat from the engine to expand the oil and push it out. After I had re-sealed these, I set them vertically on the workbench, electrical connector downward, for several days before installation. One had a trace of oil dribble out, the other was mostly dry. So, there was definitely some amount of oil inside the electrical windings. But there's no way to open this up to clean it out!

I'm hoping it's a small enough amount of oil inside the windings that eventually it will go away. However, what I don't know is if the oil can still enter the "sealed" winding after we've encased it in RTV. If oil can still get inside, it will still get pushed out from heat / pressure / etc. Grrrr.

That is interesting that oil could wick into cracks in the magnet itself. I suppose overall here the magnets are subject to lower ambient and thus engine temps so the magnets tend to be in very good condition when exposed.

I still have a few spares sealed awaiting use. And any time I see some at a parts yard I buy em to rebuild but very few parts cars around here now haven't seen one for about 2 years now.

 

[Unavita]

Nice thread. Got it!

 

[gerryvz]

My E500 has been experiencing this "stumbling" issue for the past year or so. I have had the car stored outside (under a waterproof and sunproof cover) while I have had the G-wagen in the garage for various jobs, including the cylinder head removal. More on this M104 head removal is coming soon in that appropriate thread.

The car has had the classic symptoms:

• Initial startup and running is perfect, no issues, starts right up even after not being started for a few months
• When you stop the engine, say to go into a store, and come back out, you have stumbling and misfiring
• Stumbling/misfiring/rough running goes away a bit after the engine revs up a bit, although at its worst the engine will not even rev past a certain point, limiting the car's speed
• When the stumbling engine is able to get up to speed, say 55 MPH on the freeway, and is driven for 10-15 minutes, the condition finally disappears and no issue exists. This is likely because engine has warmed up and any moisture has evaporated.

I installed new caps (Bremi/OE), rotors (Bremi/OE) and insulators (Bosch) back in 2020, when I did the top-end refresh. The cam seals (Elring) were replaced, as were the cam solenoids/magnets with new MB factory parts (Pierburg), at this time. Everything has only 8K miles on it since that time.

I will be doing the "slotting" modification and cleaning everything up, and will report back in the future to see if the condition re-occurs. Hoping to do this out in the shop after work in the next couple of days.

Never had this issue in Oregon, in Texas, or here in Maryland for the first 7 years I have lived here, while the car was fully garaged. It was only after it was outside that the issue started. Also, it will re-occur every couple of days.

 

[nocfn]

Gerry, I did all the slots and all the stuff replacements. I finally removed it all and soaked a blue shop paper towel with WD40 and wiped down all the components attached and also the area they connect to on the car. For me, that did the trick. Everything looked perfect on caps/rotors/insulators/cam seals/surrounding area. Maybe the ozone funk and any ions need to just disappear with the wd40 but honestly, there was no residue visible on the components prior to wipe down and the Scotts blue towel was also clean post wipe down. I even let it dry and it was clean. Car still humps it perfect every time after that. (all previously deep slotted and such with new caps rotors wires plugs insulators coils)

 

[gerryvz]

Gerry, I did all the slots and all the stuff replacements. I finally removed it all and soaked a blue shop paper towel with WD40 and wiped down all the components attached and also the area they connect to on the car. For me, that did the trick. Everything looked perfect on caps/rotors/insulators/cam seals/surrounding area. Maybe the ozone funk and any ions need to just disappear with the wd40 but honestly, there was no residue visible on the components prior to wipe down and the Scotts blue towel was also clean post wipe down. I even let it dry and it was clean. Car still humps it perfect every time after that. (all previously deep slotted and such with new caps rotors wires plugs insulators coils)

I'm hoping to get to the slotting today (this evening) and will report back after a few "cold starts." I will definitely be removing the rotors and insulators to check for any seepage at the cam seals, though I am not expecting any. All distributor-adjacent areas on the fronts of the cylinder head covers will be thoroughly cleaned at this time, as well as the caps and such.

I will also document everything photographically, too. Maybe I should even do a full-blown "HOW-TO" to augment this @JC220 thread on the topic. The "HOW-TO" threads seem to be a big hit with people here on the forum.

 

[gerryvz]

The "HOW-TO" for slotting the caps is now up, and available at the link below.

Thread 'HOW-TO: Solving M119 Stumbling at Ignition Distributor Caps'

Sep 5, 2025

It is a common malady to nearly all M119 engines with dual-distributor systems, sooner or later, that the engine will suffer stumbling and cutting out. This condition is because there is inadequate air circulation inside the closed environment of the distributor caps, which causes condensation to form inside of the caps, effectively electrically "shorting" the flow of electricity to the spark plugs inside of the cap.

There is MUCH more background about this condition here on the forum, in this thread: FYI - Essential M119 Ignition "Tune Up" mods [Distributor cap vent / slot] | M119...

• gerryvz
• Replies: 17
• Forum: "HOW-TO" Tutorial Articles

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[gerryvz]

I ran a first “unofficial” test immediately after completing the distributor cap repair, on a cold engine. This was an identical test to one from two nights before that resulted in stumbling occurring.

Weather was slightly hotter and more humid after I modified the caps, than it was two nights previous.

Zero stumbles. After returning home from the test drive. I shut off the car in my driveway, waited a few minutes, and restarted it yet again. And again, repeated revs — no stumbles.

I will continue to monitor this over the weekend by driving the car a few more times, but I now consider this issue to be remedied.

 

[gsxr]

I ran a first “unofficial” test immediately after completing the distributor cap repair, on a cold engine. This was an identical test to one from two nights before that resulted in stumbling occurring. Weather was slightly hotter and more humid after I modified the caps, than it was two nights previous.

Zero stumbles. After returning home from the test drive. I shut off the car in my driveway, waited a few minutes, and restarted it yet again. And again, repeated revs — no stumbles. I will continue to monitor this over the weekend by driving the car a few more times, but I now consider this issue to be remedied.

On the few cars that I've performed this modification on, that previously would have intermittent issues, the modifications have cured it 99-100%. As I've mentioned repeatedly, the oil leaks must also be completely eliminated from the cam solenoid and exhaust cam seals. If there's the slightest trace of oil at the lower edge of the cap, this issue can still pop up occasionally, even with the slotted caps.

 

[gerryvz]

Just took the E500 out for some weekend errands, including going into a couple of stores. Weather - 82F with 72* humidity.

Zero issues with any stumbling whatsoever. Idle quality IMHO is slightly improved overall, as well.

I'm going to call this problem.....SOLVED.





Monday Sept. 8, 2025

I used the E500 all day on Sunday for running errands and probably put almost 100 miles on it, including heading over the Chesapeake Bay Bridge to visit our boat at its slip. Various stops were 5 minutes up to an hour in length.

ZERO issues with any stumbling or idling/running anomalies. Ran perfectly.

I wonder how many M119s have met a premature fate, or had TONS of $$$ of new ignition parts thrown at them, simply because mechanics didn't know about the ignition moisture problems.

Now I just need to replace the front struts (I have a set of new MB front E500E struts in my parts stock), the now-20-ytear-old exhaust system (rattling rear muffler; I have the "Brabus tips" @5thscaleracer Fließen system in my parts stock ready to go); and replacing the headlight switch, which is mushy inside. I think I also need to do a brake pad replacement + brake fluid change.