I have an intermittent stalling problem.
My engine is 103.983
Today I decided to check my sparkplugs after reading on this forum that I needed to use H9DC and not HR9DC. I wanted to make sure that my plugs were not the resistor types. Imagine my surprise when it was neither .My plugs were H7DC.

Now please tell me what is the difference and should I be changing to H9DC.

I checked with BOSCH here and they carry only the resistor types.
Also the first and the last plugs were loose.It came easily in my hand.
Could this be the cause of the stalling. It has always started right up.
Also I have noticed that the stalling goes away for few days when I add injector cleaner to the fuel.

Please help.

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300CE 1989 Euro Model.
ML350 2011.

The 7 and 9 refer to the heat ranges of the plugs if my memory is correct. I was recently looking at the Bosch web site and one of the pages there gave the meanings of all the letters and numbers in the plug designations. If you Google on "Bosch spark plugs" you'll find this information.

I don't know if the HR7 plugs would cause stalling but the wrong heat range on a plug can certainly result in the plugs getting fouled. What was the condition of the plugs you removed? A plug which runs too cold will not burn off deposits and will eventually foul and misfire. A plug which is too hot can eventually have damage to the ceramic insulator at the center point and can also cause pre-ignition (pinging). Sometimes an engine which has a problem with oil fouling of the plugs can be improved, for a while, by switching to the next hotter range of plugs.

I ran into a similar problem getting the H9DC plugs as you did. My on-line supplier sent me HR9DC and told me that Bosch was recommending them to replace the H9DC plugs. However, when I went to the Bosch site I found a whole list of plugs including the H9DC, H9DC0, and several resistor plugs. The supplier told me that Bosch had told him that they were not making the H9DC plugs anymore! The Champion S12YC are also recommended by Mercedes but I've not read any comments pro or con on these plugs. Most on this forum seem to recommend Bosch. I've used NGK plugs in my Volvos in place of Bosch and have liked them.

If you do some searches on spark plugs in this forum, you'll find that folks are having problems running resistor plugs in engines with ignition systems designed for non-resistor plugs. The plug connectors and also the rotor ( I think) have resistance built in so resistor plugs may add too much resistance to the ignotion system. The purpose of the resistance is to reduce radio interference.

I have the same engine as you do. I finally went to a parts house locally and they carried H9DC0 plugs which I installed and my engine idles so smoothly I can't feel it running.

I doubt that the plugs are causing stalling unless they are fouled very badly. Incorrect or fouled plugs would be more likey to give a rough idle, poor acceleration, and poor economy. Your experience with the cleaner may be an important clue and others may have some ideas on that. In any case, I'd go ahead and install the proper H9DC or H9DC0 plugs.

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1986 300E
1993 Volvo 940 Wagon
1984 Volvo 240 (daughter's)
1976 Dodge 1/2T pickup, gas hog

H9DC plugs are the recommendation for USA engines.

Rest of world engines are likely different.

You should obtain local information.

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Kent Christensen
Albuquerque
'07 GL320CDI, '10 CL550. '01 Porsche Boxster
Two BMW motorcycles

This family of plugs is available in heat ranges 6, 7, 8, and 9 ,and the higher the number, the "hotter" the plug. For a given set of operating conditions a "hot" plug should be used if average engine output demand is low and a "cold" plug if average output demand is high - such as racing or high speed autobahn driving.

As stated, Mercedes recommends heat range "9" for most USA M103s. If you do lots of high speed driving - say over 160 KPH - a colder plug than "9" would likely be more suitable. Also, as stated, check Mercedes heart range recommendation for your typical local driving conditions.

Dukec

Thank you all for your replies.
The plug was a bit fouled.
I used to drive around 160 kms/hr but now they have radars all over the highway limited to 120 km/hr.
City driving would be 60 - 80 km/hr and freeway driving at 120km/hr.
I travel daily total 90 kms to work. i:e 45 each way.
So I believe I should find some H9DC or H9DCO plugs.

The summers are quite hot here averaging 40 to 45C. Would that affect the sparkplugs choice by any way.

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300CE 1989 Euro Model.
ML350 2011.

Spark plug tip temperature is primarily a function of engine output, not coolant temperature. The proper tip temperature operating range is 400C to 900C. Below 400 the plug will foul, and over 900 can cause preignition, which can lead to detonation.

Low speed driving in hot weather can cause high coolant temperatures, but plug tip temperature will be at the low end or the range since average engine output is low.

It sounds like your driving conditions are similar to the US, so a heat range "9" would be suitable.

Duke

NO.

Only USA cars use H9DC and H9DC0 plugs.

Get the correct plugs for your car.

__________________
Kent Christensen
Albuquerque
'07 GL320CDI, '10 CL550. '01 Porsche Boxster
Two BMW motorcycles

Now I am really confused.
Whose advice to follow.

__________________
300CE 1989 Euro Model.
ML350 2011.

Why don't you ask what's his name to justify his one word answer and tell you what are the "correct" plugs for your car. Some of these responses are just unbelieveable, but what's more unbelieveable is that some actually give them credence.

Heat range "9" plugs are not exclusive to USA models, but are also recommended in markets that don't have sustained high speed driving conditions.

Duke

Go to your local dealer.

A dealer's advice is ALWAYS better than forum advice.

You'll note here a "7" can indeed be correct for your car.
http://mb.braingears.com/124_DISC1/Program/Engine/103/15-1031.pdf

__________________
Kent Christensen
Albuquerque
'07 GL320CDI, '10 CL550. '01 Porsche Boxster
Two BMW motorcycles

You'll note here a "7" can indeed be correct for your car.
http://mb.braingears.com/124_DISC1/P...03/15-1031.pdf

This shows H7 was standard upto 2/87 and on 103.980.
As my engine is 103.983 and a euro model, I should be using H8 for normal compression and H9 for low compression if I understand it right or do I ?

Again it seems as per the manual if I use H9 I should not drive over 160Km/hr.

To be on the safe side should I use H8. what will I be sacrificing if I use H8 or after reading this link what do you think Duke2.6, should I still use H9.
I rarely would drive above 160Km/hr and only if challenged and that too in short bursts.

__________________
300CE 1989 Euro Model.
ML350 2011.

Go with 9, you'll be fine

You're kind of analysing this thing to death, but I've been known to do the same thing, so I understand.

If you rarely have an opportunity to drive at a SUSTAINED 160 KPH or greater, then your driving conditions are similar to the USA, and M103 owners have good results with H9DC or H9DC0.

IIRC the 103.983 engine is the one with 10:1 CR, where all the other 103s are 9.2, but this modest difference in CR has no meaningful impact on heat range selection. It's based on the peak sustained output demand for your driving conditions, and if you rarely have the opportunity to cruise at 160 KPH or more heat range 9 should be just fine, just as it is for USA driving conditions.

Brief bursts of full power to accelerate to cruise speed or brief bursts to 160 or more will do no harm. I do so at almost every opportunity!

Duke

kk9,

My Australian delivered 1990 300TE (103 983 engine) specifies Bosch H8DC spark plugs. For our driving conditions varying from short drives in slow suburban traffic through to highway driving fully laden at around 110km/h in 40 degree centigrade heat, the H8DC show no fouling and last easily to the specified replacement distance.

For what it's worth, my 1990 190E-2.3 (102 985 engine which is a 4 cylinder equivalent of the 103) specifies Bosch H7DC.

Greg

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107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.

Try this. Pick any number you like, and drive at the specified speed

__________________
joel

Prayers bring forth enlightenment.