Danger: RESISTOR SPARK PLUGS - PeachParts Mercedes-Benz Forum

whunter · #1 08-17-2007, 12:50 PM

Resistor spark plugs can NOT be used in many MB engine applications..
Follow Mercedes Benz specification on what spark plug to use.

What spark plug is in your engine at this moment, please remove one to check the number personally, if it has an "R" = resistor.

Do not trust service records on this.
Bad wires, cap, rotor and/or wrong spark plugs can wreck your ignition module, most applications this = $2,000.00 - $3,000.00 for a new one.

If you know your MB part number, here are links to verified Bosch Non Resistor Spark Plugs
Bosch Non Resistor Spark Plugs

Call or e-mail your VIN# to check application.

7450SE · #2 08-19-2007, 08:21 AM

whats wrong with them?

manny · #3 08-19-2007, 08:48 AM

Quote:

Originally Posted by 7450SE

whats wrong with them?

As the name ( Resistor ) implies, the resistance & load that is placed on all ignition components, with these plugs, could seriously damage the ignition module.
In simple terms, if you overload an electrical circuit in your house, you'll end up blowing a fuse/breaker.
In this case the ignition module is your fuse/breaker, but a very expensive one.

7450SE · #4 08-19-2007, 09:41 PM

That is not cool... Does this also apply to older mercs? ie '77 and back?

Tomguy · #5 08-19-2007, 10:36 PM

It sure does. No older Mercedes should have a resistor plug - resistance is built into the spark plug boot.

dpetryk · #6 08-20-2007, 09:50 AM

I have to challenge the thinking in this thread.

The previous statement:

Quote:

As the name ( Resistor ) implies, the resistance & load that is placed on all ignition components, with these plugs, could seriously damage the ignition module.

Is incorrect as it applies to ignition circuits of Mercedes Benz vehicles. I can prove it. As the resistance in a circuit goes up the "load" or current goes down.

Would the originator of this thread care to share with us the scientific or factual basis for his statements;

Quote:

Bad wires, cap, rotor and/or wrong spark plugs can wreck your ignition module.

If anybody wants to get into technical discussions on why I don't agree with this thinking I would be happy to engage them.

sbourg · #7 08-20-2007, 01:40 PM

Well, I for one don't KNOW why resistor plugs would or would not ruin an ignition module, but I can certainly dream up a technical argument for the damaging scenario...

The coil output must drop across the spark plug gap with enough initial voltage to jump the plug gap. A plasma is then created which drops the resistance of the air / fuel vapor to near 0 Ohms, allowing a lower source voltage from the coil to push enough current across the gap to complete the ignition process. If the series resistance of the wired path is too high, the lowered energy flow rate to the gap could be insufficient to sustain the plasma, and the spark will die. For the remainder of the spark cycle, the full output of the coil will then appear across the coil terminals, risking internal breakdown over time. Now I don't know that this would actually occur if resistor plugs are used, but I would like to hear the technical reason refuting this possibility.

Steve

whunter · #8 08-20-2007, 01:40 PM

Quote:

Originally Posted by dpetryk

I have to challenge the thinking in this thread.
The previous statement:
Is incorrect as it applies to ignition circuits of Mercedes Benz vehicles. I can prove it.
Would the originator of this thread care to share with us the scientific basis for his statements;
If anybody wants to get into technical discussions on why I don't agree with this thinking I would be happy to engage them.

Personal/professional experience and MB TSB/public announcement data on this issue is fact.

I do not have time to dig up all of the data.

If you desire to discuss your opinion, please start another thread.

dpetryk · #9 08-20-2007, 03:05 PM

Well, if you or someone else can get some time to dig up the TSB, I would love to see it.

I called 4 MB dealers in Houston and none of them could remember anything describing the TSB mentioned here. This does not prove that it does or does not exist, just they had no memory of anything related to the use of resistor plugs being detrimental to the ICU.

Owning 5 vehicles, and having resistor plugs and wires, I am concerned about the possibility or risk to the ICU. I would like to know for sure. I think everyone else would also.

Certainly someone here has access to the TSB's and can confirm this one way or the other. Is the TSB specific to all cars or only to certain years / models? We need to know.

For me personally, I am not concerned. But I would like to know the official word on the subject.

lkchris · #10 08-20-2007, 04:39 PM

Presence of a TSB (supposed) indicates Mercedes has a solution and you can get proper plugs or plug/wire combinations at your dealer.

It's patently ridiculous to think anything else.

And, I'd be surprised if Mercedes' solution doesn't include Bosch plugs.

waybomb · #11 08-20-2007, 08:53 PM

The first time ever changed plugs on any Mercedes was with my first MB, the 97 C280. I put resistors in. Mistake. Did not run well. I thought I broke an insulator or something (kinda hard to do when the things screw straight down from the top). So I bought another set! Then I figured something was wrong with my plug choice.

Then I found mercedesshop, read all about as a lurker back then, and went to the dealer and bought the correct plugs. Ran as it should after that.

As for plasma, etc, I don't know, but the correct plugs make things right. There isn't too much you can do on these cars cheaply that will result in improvement, as I have found out after owning these things for 10 years now.

manny · #12 08-20-2007, 08:59 PM

sbourg

You explained it pretty well.

Waybomb

FWIW, my 2000 C 230 K had Bosch F7 KTRC sparkplugs OEM.
Notice the " R ", it's a resistor plug.
Life just ain't that simple anymore.

zcc · #13 08-22-2007, 04:39 AM

Guys, I found you a great site: http://www.nightrider.com/biketech/faq_ignition_wires.htm

waybomb · #14 08-22-2007, 07:20 PM

Quote:

Originally Posted by manny

sbourg

You explained it pretty well.

Waybomb

FWIW, my 2000 C 230 K had Bosch F7 KTRC sparkplugs OEM.
Notice the " R ", it's a resistor plug.
Life just ain't that simple anymore.

All I was saying is use the correct plugs for your car. If your car's service manual indicates the use of a F7KTRC plug, then use that plug. Don't try to make it "better".

dieseldiehard · #15 08-22-2007, 07:33 PM

Quote:

Originally Posted by whunter

Personal/professional experience and MB TSB/public announcement data on this issue is fact.

I do not have time to dig up all of the data.

If you desire to discuss your opinion, please start another thread.

Awww, I think this thread is still the place to discuss the subject. As an EE I would like to know the reason for an announcement, to see if its based on technical or other basis. It could be a simple warning to keep sales up on MB instead of aftermarket parts. I think its pretty rude to try suggesting starting another thread. Tech help matters are open to discussion too aren't they????

Show us the details, Mr Hunter