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