Hi,

Sorry to high jack this thread. Considering changing my plugs, can someone tell me the right plugs for 1992 300E m103. I have beru wires and have changed one resistor end that was arcing but never took the plug out so not sure what's in there.

Thanks, Jeff

I had a awd eclipse turbo that was experiencing ignition issues after installing platinums. keep it oe always. car ran smoother after installing ngk copper fours.

Folks,
Am I correct in saying that spark plug wires for Mercedes do all of the necessory "resisting" and that's one reason to NOT use resistor type of plugs? I've seen some part places selling generic style radio noise suppressant (resistor) wire and regular resistor plugs for Mercedes and push the heck out of over priced platinum plugs.
I use OEM wires and the H9DC's. Never a problem.
John

< John
>>

.. and your Ignition components thank you for it..

Putting resistors on top of resistors is like tieing a knot in you garden hose..

Your analysis is basically correct. IIRC when I measured the wire resistance on my M103, all were about 2K ohms regardless of length. My understanding is that the wires have a discrete resistors that are part of the spark plug terminal, so the wires themselves probably have very little resistance. It's also my understanding that the cap has resistors - about 1 or 2K ohm - built into each cap terminal.

Mercedes implemented a unique solution to the RFI suppression requirement. Rather than using conventional resistor spark plugs and RFI wires they have discrete resistors built into the spark plug terminals, cap terminals, and require non-resistor plugs to achieve the design secondary voltage wave form.

If you use anything other than Mercedes OE equivalent spark plugs, spark plug terminals, wire, or cap you're asking for trouble.

Duke

They're listed in your owners manual - Bosch Super (conventional copper core) H9DC0 (OE) heavy duty electrode or Bosch Super H9DC conventional electrode. You probably won't find either at McParts but both are readily available from Fastlane, and I recommend the standard electrode H9DC, which are about two bucks each.

McParts may have HR9DC, but the "R" indicates a resistor plug, which you DO NOT want.

In fact, Pep Boys has Bosch Supers on sale for a buck each, so I'm going to pick up a set or two of HR9DC for my Cosworth Vega, which uses the same geometry/heat range as M103, BUT in a conventional resistor type. I already inquired if Pep Boys can get H9DC. They could not even special order them.

Duke

Thanks Duke, appreciate it

I replaced the HR plugs with H9DCO plugs from the dealer today and I must say the difference is noticable. Any one wanna buy some Platinum Bosch Plugs ???

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190e 2.6 1990. 300,000 KM
C230 K 2000, 130,000 KM

<< they have discrete resistors built into the spark plug terminals,>>

Just a note on this.
The advantage of resistors on the end of solid core wire is that every wire , regardless of length, has the same resistance .. whereas , resistance wires measure R per foot, resulting in the longer wires getting much more R then the shorter.
Uniform R is much better.

Yep, that's what I found when I was troubleshooting high HC for the first time about ten years ago, and it's a better design because the constant resistance regardless of wire length means maximum energy at each plug rather than a plug at the end of longer wires being short-changed with conventional constant ohms/foot RFI suppression wire.

The consistent 2K ohm reading for all wires regardless of length had me perplexed, but I also had the single electrode Bosch Platinum plugs installed, so I replaced them with a set of H9DC and the HC emissions dropped in the next test.

Since then I've learned more about the Merc ignition system and now understand why resistor plugs are problematic as I explained previously - upsets the design voltage waveform - and reduces ignition energy at the electrode due to the addtional secondary resistance.

Again, the "problem" with the single electode Bosch Platinums is their resistance and any other resistor type plug could cause the same problems - high HC and rougher than normal idle due to misfires. The multielectrode versions are worse because of the heat sink effect of the multiple electrodes.

I keep a set of H9DC in my spare parts supply, so I have them on hand whenever they are needed.

Duke

Whenever I relpy to a 104 eng plug/misfire problem [ which is usually bad resistor ends under the 3 coils], I always end the post with "F8DC4,Super Copper - NO OTHER ".. without going into detail..

..to explain it , these 104 HFM cars use a waste spark ignition , where the coil fires 2 plugs , in series.. so, right from the start, you have double the resistance and gap to overcome, but the important word here is 'Series Circuit"
One wants a large electrode b/c the first plug fires from the electrode to ground , as any normal plug... but , b/c it is a series circuit , the second plug in the chain now has to fire up from ground TO the electrode before completing the series circuit..well, guess what happen with small electrode, resistor plugs ???

.. and because these HFM ignition systems immediately cut power to the fuel injectors as soon as the ECU sees a misfire , you wind up with a crap running engine that will, when everything ignition related is OEM, run superb..

It is a very hard thing for a reply poster to try and convince a 104 eng. owner that has just gone for the Hype and spent a good piece of $$$ on Plats to take them out and get the Cheapo Supers and his car will run new..

You will do better trying to teach the dog algebra..

Do i run resistor or non resistor plugs on m112 engine? thanks

OK update:

I had emissions test performed again today, and passed with flying results. Both HC (ppm) readings at idle and 2500rpms were below 20, the limit being 200! Considering I failed the emissions prior to switching to the proper spark plugs. But in all fairness (according to my experience) I must say that the NGK plugs lasted atleast 15K before showing noticable signs of failure. But one questions still remains, I was hoping that the proper spark plugs would return my high idle to normal again, but so far no luck.

__________________
190e 2.6 1990. 300,000 KM
C230 K 2000, 130,000 KM

When I lost idle control the problem was the throttle valve switch. It wasn't sending the idle position signal. The TVS has a pigtail that connects to the engine harness at the top-front of the inlet manifold with three poles - idle, WOT and ground, so it's easy to test just by unplugging this connector and testing at the pigtail.

I was able to restore TVS function with a good external cleaning, which is fortunate, because it looks like you have to remove the metering unit to change the TVS. The two screws just aren't accessible on the car.

Duke

Correct, while I was replacing my top timing cover seal, fan clutch, bearing bracket and both hoses that connect to the idle control valve I had the air flow meter out I cleaned the Throttle body surface and installed a new gasket. I checked the TVS but I must admit at the time my car had been out of action for a week and I couldnt afford to keep the rental anymore so I couldnt continue to diagnose the problem properly but my next project will be to diagnose the wiring harness to the TVS. I also have another unit I picked up from a junk yard and could possibly salvage the switch from it.

__________________
190e 2.6 1990. 300,000 KM
C230 K 2000, 130,000 KM