Replaced Spark Plugs...and wow!! what a difference!
 

I had noticed my car not responding as well recently. When coasting at around 40pmh, if I openned the throttle wide, the car would hesitate to speed up. Also my car was running very sluggishly, vibrating in a word. What I had previously believed to be a fuel filter related problem, turned out to be my spark plugs that I had replaced when I bought the car with NGK TR5GPs. This was last July (2004) I have driven about 30K since. Well I figured I might as well check out the plugs, turns out that plugs 3 and 6 and a lot of gunk and seemed oily. While the others had little or no gunk and werent oily. They were dry and had a greyish residue over them.

Well I replaced the plugs with Bosch platniums. And the car responds a lot LOT better to sudden acceleration.

I am just curious why only the plugs from cylinder 3 and 6 were dirty and not the rest?

You 'may' not want to find out. Could indicate valve problems .... among others

cheers, guenter

I would consider using non plats. The spark on the plats isnt that big and that could lead to your fouling problem.

The plats are a no-no. Use only what the owner's manual suggests.

Your fouling problem will eventually return. The rear most plugs are fouling first, no?

YOU SHOULD NOT USE RESISTOR PLUGS ON MERCEDES!!! The ignition system is very carefully designed for use with non-resistor plugs. Resistor plugs add secondary resistance is excess of design specs and alter the secondary voltage wave form.

Sooner of later you will have problems such as rough idle or high emissions.

The proper plug is Bosch H9DC (NOT the HR9DC resistor type), and these are not commonly available at McParts, but are readily available for two bucks each from Mercedes parts specialists like Fastlane, which sponsors this site.

Any spark plug with an "R" in the designation is a resistor type and should NOT be used.

Duke

Ok understood, I changed to non-R type I believe but I will double check.

OK I found out that the plugs I bought were HR9DPX Bosch Platinum. But what I do not understand is why these plugs were listed in the car parts catalogue as the appropriate plugs for this car. Also when I originally bought the NGK plugs, from NAPA parts, they looked it up in their system and sold me these plugs. So are the major retailers are not aware of this resistance problem????

Most parts places are supposed to know better then to sell platinum plugs and what not for cars that aren't made for it. Problem is, Bosch and other companies are giving McParts better deals on plugs if they sell more platinums. Bosch double and quad plats usually get the salesperson a little comission too. The parts store IS able to get H9DC0's... you just need to ask them to order em. If they say they can't get them, they just don't feel like doing a special order.

Platinum and copper plugs
 

I don't understand the purist approach to plugs in Mercedes. I have installed Plus 2 and Plus 4 plugs in lots of cars, including Mercedes and never have a problem with the car's performance in any way. The fact that a plug has platinum coatings does not mean it is harmful; it just means it should last longer ..... My experience with the platinums has been good.....

The issue is not "platinum" versus conventional copper core plugs. It's resistor versus non-resistor and Bosch Platinums HAVE RESISTORS. This must be the sixth time in the last year I've made this point!

Most aftermarket manufacturers list resistor plugs for Mercedes which have non-resistor plugs as OE. They just don't care. Most don't offer non-resistor plugs in the correct heat range and geometry, so they just list resistor type plugs.

Take a look at the service CDs. They have several examples of both normal and anamolous of secondary wave form traces and show at least one with excess secondary resistance. It may not result in any noticeable difference when the plugs are new, but as they age - wear and build up deposits, the number of misfires will increase resulting in more idle roughness and higher emissions than if the proper non-resistor plugs are used.

Bosch H9DCs (for M103 engines) cost about two bucks each and have a normal service life of 30K miles. The H9DC0 has a "heavy duty" electrode. They were OE, but they are more expensive, and the standard electrode H9DC work just as well over the 30K service interval.

Spending more money to by the WRONG plug is just plain foolish!

Duke

I agree with Duke's last comment...H9DCO vs. H9DC.

I've used both and actually got better gas mileage and a smoother idle with the cheaper H9DC.

Yea,

When I worked in a shop- we always put in OE plugs. So mercedes got copper core bosch plugs, Jap stuff got NGK's, Jags have Champions etc. I think it was the 930's which had the thick electroid plats which were expensive. Never had problems except stocking would have been easier with one companies product.
I understand at the user end, someone looks up a plug and it "fits". That doesn't mean it is equivlent. I seem to remember turbo cars had more problems with bosch platinums than others. Seems the platinum heat range(look in the back of the bosch catalog) is over a larger range than a standard plug. So, I'm guessing, it fit the size and range but was not centered and performance problems erupted.
blueEagle289. The M103 engine seems sensitive with it's ignition system. May not matter as much on the newer stuff,so your experience maybe fine for later engines... but not the M102/103.

Michael

When the spark initiates a tiny flame kernel, the spark plug electrodes represent a BIG COLD HEAT SINK relative to the 4500F temperature of that tiny flame kernel, and the flame can be quenched by a big heat sink, which results in a misfire.

"Fine wire" electrode plugs - usually "double platinum" - both the center and fine wire ground electrode can be advantageous in high performance engines with marginal ignition energy, but this harks back to the days of mechanical breaker points. Modern electronic systems going back to the seventies have at least double the per spark energy of breaker point systems. I've seen plugs come out of mid-seventies GM products with HEI systems where the center electrode was worn nearly to the insulator and you had to measure the gap with a ruler, but the engine basically ran fine. When you have a "fancy" ignition system, you don't need anything more than a plain vanilla two-dollar spark plug.

So conventional electode plugs work very well with modern ignition systems. These Bosch Platinum plugs that are heavily advertised and sold at McParts are junk and defy every theory of ignition and flame propagation because all those ground electodes are a HUGE heat sink to an incipient flame, so there are going to be more misfires, which eventually means rougher idle and over the limit HC emissions.

Bosch is really prostituting their name by selling junk like this along with the "fake Bosch" oil filters at Autozone. It used to be a name you could trust, but now you have to verify which distibution channel their parts come through, and if it's McParts, beware.

The same argument applies to the H9DC0 because of the larger electrodes, and I'm not sure why Mercedes used them as OE because the standard size electrode H9DC performs well and will easily make 30K miles unless you have high oil consumption or a fuel mixture problem.

Duke

Just to add to Duke's comments about platinum plug issue,

I have about 10 years of The Star magazine, and the technical editor wrote a very informative article about platinum plugs, and why they are specifically not recommended on engines that weren't designed with these plugs in mind.

The article specifically referred to M104 and M103 engines.

This does not apply, however, to engines that were designed with these plugs in mind, like M112 and M113 engines.

If there were non-resistor platinum plugs available for M103 and other Merc engines of the era whose ignition systems are specifically designed for non-resistor plugs there would be no issue, but the heavily advertised and widely available "Bosch Platinum" spark plugs are only available in resistor type, and resistor versus non-resistor remains the fundamental issue.

All the redundant ground electrodes on the multielectrode versions are also a major issue and further reason not to use these plugs.

Duke

proper plugs for 1992 300E m103
 

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

<<I use OEM wires and the H9DC's. Never a problem.
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 ??? :D :D :P

<< 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.

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.