In an earlier post I mentioned problems in getting the Bosch H9DC plugs. Below is my message to the supplier about the supplier's mistake in substituting HR9DC plugs for H9DC. What do the Forum members think about the supplier's statements that Bosch isn't making the H9DC anymore. Is this true?

>Dear Tom,
>
>Thank you for your reply and the credit for the plugs. That makes me very
>satisfied with your service.
>
>Regarding using the HR9DC plugs in place of the H9DC, the HR9DC plugs are
>resistor type and the H9DC plugs are not. The spark plug wires on my
>Mercedes have a resistance built into the plug connector already. Adding
>additional resistance to the spark plug could very well upset the
>operation of the spark circuit. I believe the spark oscillation would be
>over damped. To use resistor type plugs in this engine, I'd have to
>replace the spark plug wires and connectors with non resistive parts.
>
>I follow the forum at Mercedesshop.com and the people on that forum report
>ignition problems when they use resistor type plugs in engines which were
>not designed for them. Several have had very poor operation with resistor
>type platinum plugs. I'd be reluctant to use the HR9DC plugs for that
>reason. I'll post a question on this specifically and see what answers I
>get. Several of the forum members are professional Mercedes technicians.
>
>When I bought plugs locally for my car, they provided HR9DCO instead of
>HR9DC. These plugs are much the same as the HR9DC but the center electrode
>is larger. You might check with your supplier to see if the HR9DCO has
>superceded the HR9DC plugs.
>
>Again, thank you for your prompt replies to all my emails.
>
>Jim Holst

The supplier's reply to my message was:

Jim,
I had a very similar conversation with one of the parts experts on this
subject yesterday. He told me that he is not quite sure how Bosch has gone
from advertising the need for resistor type plugs for thirty years to now
saying that they are the same. However, that is exactly what Bosch has
done. This supersession does not come from XXXXXXX, it comes directly
from Bosch. I don't know if they have made HR9DC in such a way that it can
work in a wider variety of applications but I do know they don't have any
more of them left in the U.S. Since these plugs were used on some of the
best selling Mercedes from the '80-90s it seems strange that they would
leave thousands of cars high and dry without decent spark plugs.
I did check for HR9DC0, but I could not find any listings for them. I also
checked my Bosch spark plug catalog and I could not find them there either.
However, my catalog is a couple of years out of date so, it is possible
that they are new type that are not currently available from all sources.
If you do find any other information from any forums or message boards,
feel free to pass it on.

Best Regards,
Tom

I'd be interested in knowing if this information is accurate.

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

I have nothing to add other than a suggestion.

When you start a thread it would be helpful to make the title specific to
the subject. Something like "Sparkplugs H9DC Unavailable"

"Has anyone heard about this?" is meaningless.

No offense meant, just trying to make the forum more useful.

Steve

Steve,
Thanks for your suggestion. You are quite right and I've edited the title for greater clarity.

Jim

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

H9DCO is a good substitute for the original plug, you may notice a better idle quality as well.

Not sure if I could add anything useful regarding Bosch's manufacturing decisions. A penny times a billion equates to serious dollars, who can blame them for saving as many pennies as possible where ever they can.....within reason of course.