Why non-resistors plugs? - PeachParts Mercedes-Benz Forum

JamesDean · #1 03-01-2007, 09:21 PM

hey everyone,

a friend of mine asked me why non-resistors plugs on my m103 engine...and i really dont know why...i just know that what it uses...so mb guru's why do only use non-resistors? what doesn't our motor's like about the resistors?

-kris

okc329 · #2 03-01-2007, 09:44 PM

if the M-B engineers have specified spark plug cables with a certain amount of electrical resistance, they have in mind a certain firing voltage across the plug for the hotness of the spark desired. If the plug is a resistor type, then some of the desired sparking voltage is dropped in the plug and not available for the magnitude of sparking desired. If the spark is less than desired, combustion is not as strong or complete and the power from the detonation in the cylinder is diminished. Yhink of it this way. If the fireman responding to your house fire takes the nozzel off of the hose and inserts a length of garden hose between the fire truck's hose and the nozzle, he won't be nearly as effective fighing your fire!

langpfeife · #3 03-02-2007, 01:24 AM

Well, although Bosch says it's OK to run their resisted plugs as replacements (and MBs use a Bosch ignition system), I agree that resisted plugs are probably not "ideal" for the reasons already stated. I delved into this a bit a few years ago, and according to MB tech info from the era (I didn't have access to WIS back then) the extra resistance from the newer Bosch plugs certainly won't hurt anything, still well within the allowable range -- contrary to what I've heard some mention on another board. (Of course, there could be some more recent info that I'm not aware of, and I'm certainly open for correction here.)

I've seen cars with aftermarket wires using 5k plug-end caps (should be 1k on most, the 5k caps are supposed to reduce interferance a bit more) *and* resisted plugs, they run OK, and in some cases have for several years. It's certainly possible though that the resisted plugs may not last as long, and FWIW I run non-resisted plugs.

EDIT -- Just a thought here, but I've personally not seen proof that a resisted plug will diminish the spark so much that it would cause incomplete combustion, hamper performance, economy, etc. Becasue it's resisted doesn't necessarily mean that there isn't enough juice across the plug for complete combustion. My $0.02 anyhow...

#4 03-02-2007, 08:15 AM

IF your ignition system components are all in good shape you will not experience problems with resistor plugs, but they are unnecessary. The resistors are in the plug sockets. Using resistor plugs in addition to those is adding additional, unnecessary resistance.

Arthur Dalton · #5 03-02-2007, 09:26 AM

Quote:

Originally Posted by langpfeife

...EDIT -- Just a thought here, but I've personally not seen proof that a resisted plug will diminish the spark so much that it would cause incomplete combustion, hamper performance, economy, etc. Becasue it's resisted doesn't necessarily mean that there isn't enough juice across the plug for complete combustion. My $0.02 anyhow...

The burden of extra resistance is most evident in the Waste Spark ignition systems of the 104 engine chassis. these sytems fire 2 plugs from one coil , but they are a series circuit, so any additional resistance is doubled and will definately effect performance...and they also tax the coils and ECU switching transistors.
Plenty of info in the archieves confirmng this fact.

david s poole · #6 03-02-2007, 10:58 AM

they way i understand it and what i have personally observed is the following:extra resistance causes all of the components to work harder.you don't lose spark intensity in fact the opposite is the case with static electricity.BUT----i have seen the distributor caps ,rotors and wires burn up from too high a current.the extra resistance forces the voltage upwards by several hundred so that it can jump the gap.in some cases benzes running the auto part shop favourite bosch platinums have burned up the ignition unit.[remember when gm was running 80 thousand gaps and first started resistor plugs,how long did the coils in the distributor caps last?] i think that so many cars these days are designed for resistor plugs[and it's only the older benzes that use non resistor ] bosch has thrown us to the wolves and made their decision for economic reasons.

Arthur Dalton · #7 03-02-2007, 11:25 AM

Quote:

Originally Posted by langpfeife

...EDIT -- Just a thought here, but I've personally not seen proof that a resisted plug will diminish the spark so much that it would cause incomplete combustion, hamper performance, economy, etc. Becasue it's resisted doesn't necessarily mean that there isn't enough juice across the plug for complete combustion. My $0.02 anyhow...

That is exactly what has happened .. the newer ignition design specs. take the plugs resistance into consideration for spark control from the ECU triggers, but b/c they no longer are making the non-resistors , they throw the resistors/plats at you for the older systems and claim they fit.. well, they fit alright...but we know they don't work too well.
Bottom line..if the original equipment specs call for non-resistor plugs, that is what is needed to get optimum spark/timing/duration for that system.
And if you can't find them in Bosch, get NGKs ..
Don't tax your ignition system, you will be sorry..

joel · #8 03-02-2007, 01:58 PM

Quote:

Originally Posted by Arthur Dalton

That is exactly what has happened .. the newer ignition design specs. take the plugs resistance into consideration for spark control from the ECU triggers, but b/c they no longer are making the non-resistors , they throw the resistors/plats at you for the older systems and claim they fit.. well, they fit alright...but we know they don't work too well.
Bottom line..if the original equipment specs call for non-resistor plugs, that is what is needed to get optimum spark/timing/duration for that system.
And if you can't find them in Bosch, get NGKs ..
Don't tax your ignition system, you will be sorry..

just gone through this recently. it appears only Beru brand still carries the non resistors.

will someone please chime in, i believe the answer to this dilemma is to change the plug wires to be compatible to the resistor plugs!

Arthur Dalton · #9 03-02-2007, 02:11 PM

< >>

To what?? Resistor wires ???
Benz wires have NO resistance.. they are solid core wires ..the resistors are on the ends of the wires in thew plug connectors..so, you are putting resistor plug connectors on top of resistor plugs..doubling the resistance.
If you eliminate the plug connector/resistor end, and leave the solid core Benz wires , you may come close to stock with a resistor plug. But changing wires gets you nothing b/c you can not get wires with LESS resistance than the stock wires..
The reason Benz uses solid core wires is b/c resistor wires have resistance by the foot of each wire , so every wire , being different lengths, has a different resistance. benz find that unacceptable..and solid copper core wires are far superior ...........every plug gets the same resistance [ and thus, the same voltage], regardless of the differing lengths of plug wires. The triggering ECU likes that resistance consistancy for each and every cylinder.

anthonyb · #10 03-02-2007, 04:04 PM

Quote:

Originally Posted by joel

just gone through this recently. it appears only Beru brand still carries the non resistors.

You can get NGK non-resistor plugs, but they are only sold in the European market - I picked up a half-dozen recently from a UK retailer on eBay.

Arthur Dalton · #11 03-02-2007, 04:07 PM

Quote:

Originally Posted by anthonyb

You can get NGK non-resistor plugs, but they are only sold in the European market - I picked up a half-dozen recently from a UK retailer on eBay.

You can get them in US at any Motor Cycle shop...or Speed Shop/Import Parts place.

83scrambler · #12 03-02-2007, 04:18 PM

Upon looking into this problem myself as I was prodded to change out my coil to plug connectors, I took some measurements. I found that two of the connectors were measuring 2k ohms and I found one that measured 2.7k ohms. I then measured the new connectors that I bought and the all measured right at 2k or 1.9k ohms. The car runs much better with a noticeable difference with the new connectors.

Pretty much what all the crap means is that even 700 ohms can make a huge difference, I know that it did with mine.

PS I have resistorless plugs on the way and will report on my findings there in resistor measurement as compared to the bosch plats i am running right now.

sokoloff · #13 03-02-2007, 05:17 PM

NAPA carries NGK plugs.

whunter · #14 08-26-2007, 04:38 PM

here are links to some verified Bosch Non Resistor Spark Plugs
Bosch Non Resistor Spark Plugs

We carry them.

JamesDean · #15 08-27-2007, 03:56 PM

well i finally got an email back from Mercedes regarding the plugs...

"Thank you for your Internet message.

We are unable to address your inquiry from this vantage point. For repair
and maintenance information about your vehicle; however, repair
CD's/literature may be ordered through the Customer Assistance Center at
1-800-367-6372. Additionally, repair information is available at -
www.startekinfo.com.

The opportunity to respond is appreciated.

Regards,
Lois G.
Customer Relations"

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