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

JamesDean · #1 03-01-2007, 08:21 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, 08:44 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, 12:24 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, 07:15 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, 08:26 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, 09:58 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, 10:25 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, 12:58 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!

JamesDean · #9 08-27-2007, 02:56 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"

Graham · #10 10-26-2007, 04:37 PM

Camelot,
After going through the same exercise as you, I think that I now a slightly better understanding!

MB wanted all wires to have the same resistance and at same time prevent interference with the radio and electronic engine components.

What they did, was use a very low resistance wire (stranded copper), and then they added a resistor at each end in the caps. My old wires measure 8kohms from end to end, the two reisistors are 1.6 and 6 kohms for 7.6 total, so wire is about 0.4 kohms for total of 8 kohms. (Using my old multimeter).

If new Bosch spiral wound wires are used, the wires them selves will have a resistance. I measured mine at 1.6 kohms end to end. If non-resistor plugs are used, this would mean your total resistance would be 1.6 kohms and it would change with length - Difference could be as much as 20%. If you use resistor plugs with say 5kohms resistance, then the affect of the differing wire lengths would only be about 5%. So, it seems to me that it would be advisable to use resistor plugs with wires that do not have built in resistors.

BUT, to add to the confusion, Bosch say this on their site:

Not with Bosch Premium Wire Sets. Electromagnetic interference (EMI), also called radio frequency interference (RFI) is caused whenever a current flows through a wire. This current creates a magnetic field that can disrupt other sensitive electronic components such as the engines electronic control unit or radio. For Japanese and domestic applications, Bosch wire sets have a RFI absorbent shielding material to eliminate interference. In European applications, a solid copper core wire is used with OEM-style resistor connectors that absorb unwanted EMI.

The Bosch Premium Wire Set box says it is for MB V-8 engine, but the wires do not appear to have built in resistors and a resistance check confirms this.

I called Bosch, but just got the run around - the guy was not knowledgeable and just wanted to get me off the phone. Bosch Canada did not respond!

It would be nice to put this subject to bed. But without cooperation from Bosch, that won't happen!

I wish I had bought the Beru wires. Their website provides extensive info on their wires and plugs:

For example: http://www.beru.com/download/produkte/endverbraucher_zt_e.pdf

CamelotShadow · #11 10-26-2007, 05:04 PM

resistance of the wire is the same at any given point
but the longer it travels the slower it will become
So as the lengths vary a bit
I suppose what they did was to add a compensation factor to the end of the shorter ones so that the energy would travel at the same speed even though some had a longer distance to travel

Now that does make sense to me...
as you want to fire the plugs at the appropriate times wo the travel time lag which I don't thinkin a few inches is alot
but its good to have it compensated for

I measured the bosch wires
they were not exactly the same as the MB

Yeah would like to see what Bosch is doing
but it seems like they are not adding that compensation factor to bring the end voltage at the same time in all the wire lengths

I think what really matters is that the end resistance in all the lengths be the same.
You didn't measure each one did you?

That would interest me

I'm thinking the most important thing here is the timing as you want to ge that spark thru to each plug at exact same time wo additional delay from extra resistance caused by longer travel length.

The way I understand it the plug should be able to handle the resulting voltage & only as much that iis necessary willbe used to jump the gap

The equation is
E=IR

I is current
R is resistance
E is voltage

I don't see a factor for distance etc length of wire
but it has to comeinto play
I think?????

current is in sense s time distance factor
as its what moves thru the wire
& its speed is affected by the resisitance of the wire
Maybe resistance is not cumulative?

Its been a lone time since I took physics & electrical courses

LOL

HELP

Where r the electrical gerus'