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

__________________
Master Computer Engineer, A+, Network+, MCP/MCSA/MCSE 4/2k/2k3 - Messaging, MCTS, MCITP, MCT, Brainbench, ICDL and starting Ph.D

380SE 1984 <------- Totaled by flipping accident
300SE 1988 <------- Sold
Volvo S70 2000 <---- 4 family
Opel Omega 2002 <-- 4 family
560SEC 1989 <------ Sold
560SEL 1990 <------ Sold
560SEL 1991 <------ 4 my mother
560SEL 1989 <------ Sold
600SEL 1992 <------ Current

http://search.ebay.com/_W0QQsassZkhazenzcc

I believe the M119 and the late M104 engines are less susceptible to the resistor issue. Both engines are a double overhead cam design with 4 valves per cylinder and variable valve timing on the intake side with fully electronic and integrated ignitions. One coil for two cylinders. There is a lot of adjustability in these engines, not as much as the newer engines MB has now but I would say enough computer control to compensate and benefit from platinum resistor plugs.

The M103 and M102 engines on the other hand are traditional single coil designs with no variable timing. Resistor plugs do cause issues especially if the coil is an old (original) one. But this is just based on my experience, no technical document or lab test was performed lol

This makes for some interesting reading & it's in layman's terms:
http://www.ultralightnews.com/enginetroublshooting/resistorcapsandplugs.htm

__________________
2007 C 230 Sport.

The problem with resistor plugs is not the current but the voltage. The firing voltage may get too high and damage ignition system components.

Huh?!? Wanna run that one by us again? Please explain.

__________________
MBCA Member #B012089 (Lone Star Section)
OBK Member #47 (W123 Division)
'96 SL600 (105K) Triple Black - Mein über-Fräulein
'79 240D (292K) Yellow/Saddle - Mein Spielzeug
'01 ML430 (123K) Black/Saddle - Wife's Ride
'94 SL500 (164K) Green/Champagne - Daughter's Dream
'73 450SL - RIP
'86 300E - RIP
'88 420SEL - SOLD
'94 S320 - SOLD

When resistor plug used, you add the resistance of the plug to the total resistance already there - in the plug connector and in the rotor or cover (not sure were the resistor on the distributor side is). The resistance of the path from the coil to the plug will be higher than normal. This high resistance puts additional demand on the secondary voltage to initiate and support the spark. It is like having a bad high voltage wire.
Mike

Wow, I love this site!! No bull.. here. We'll not much anyway. I started waxing so first: I just replaced 12 plugs on a E320. Single electrode Bosche, 88k miles on plugs, engine running poorly, so I guessed and got it right. I didn't notice if resistant or not. But the new plugs were dual prog Bosche. Old plugs had the fine point and single plated wedge ground. Inspecting them I could see worn multiple tiny bumps on the electrode near the ceramic and much ware on the wedge. I wish I kept them to look again. I remember tiny nodules on the electrodes, too. You need a magifier to see them well. Rounder surfaces and wear giving wider gap requires longer time for the voltage to build before it can jump and harder to sustain = shorter spark.

Why Two plugs? A clue is two coils, one for each plug. I'm guessing the computer can fire the coils independently and the best use of that would be to give a longer spark.

We used to file the old plugs to give sharpe surfaces at the edges for the spark to jump from and to, reducing the needed voltage and increasing the time the spark continues. The lower the voltage the longer the gap sustains the spark, given equal losses (gap mostly) accross the gap. The multiple electrodes allows for more wear points for the gap. Spark jumps the shortest distance first. I've never looked to see if multiple sparks occur, but my thoughts are if multiple jumps occur, the gap is broader and can distribute the spark leading to a longer duration spark in the chaotic environment of ignition and more surfaces allow longer plug life. My assumption is the 4 prong plugs don't all fire at once, but share the duty maybe unpredictably. I'd love to see the process captured in a video.


Waxing on ignitions: Excellent explanations of the spark / coil circuit and the issues of getting a spark and sustaining it. Nothing better than presenting factual knowledge as opposed to what people think. Its amazing that people believe its true just because they think it.

I've been in electronics since the 50's and saw the first transitor ignitions come in. Incredibly, mechanics put ice picks through the insulation to measure dwell!! I worked in a ford dealership (1965-66) and the mechs routinely pulled the new transistor point units because they didn't understand them or how to measure new low current dwell signals with old equipment. But they were sure they were doing the right thing without trying to understand.

Keep the high level of technical knowledge flowing, Please!

Hi guys!
Great thread and I am very pleased to see I can get the non resistor plugs for my W124 wagon!

I am really struggling trying to fix this misfire I have. I tried another place which stated the non-resistor but they sent me resistor which was very frustrating.

I just ordered a set of the Non-R's and I am praying that it will fix my misfire! Will post back with the results when I get them! I currently have resistors in.

__________________
2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k

New specs for new Bosch plugs are out,the new "R" plugs add hundreds, NOT thousands of ohms resistance ,the same amount that is added as systems (plugends,wires,caps,rotors)break down naturally.The backstock of old part #s will be depleated,then what will you do??SO....................for those who have nothing but time,ohm out the complete assembly:"R" plug,resistor end,wire,and boot end,WHAT DO YOU GET.............thats right.............not much.Lets get back to fixing Mercedes!!

__________________
1982 300 td. 268k
1984 300d .345k
1986 190e 2.3 16v
1988 190e 2.3
1989 190e 2.6
1991 300e
1984 318i

Curious where you got the info. on the new specs of the plugs. If the resistance levels are that low for the 'new' units, then there should be no worries with using the 'new' plugs.

Wondering if anyone has thought about putting some non resistance ignition cables together and allowing the plugs to do all the work. Or was it the plug end that had the resistance built in? Just my thoughts.

I have read this thread and it seems no one actually narrowed down the problem of too much resistence in the ignition system. Any one who has ever used a lab scope on the ignition knows you look at the primary side of the coil and get a good indication of what is going on in the secondary. Bad plug wires, rotors, fouled plugs, etc are clearly displayed. This is the results of the secondary inducing a signal back into the primary. If the resistance is low (fouled plug) the secondary voltage will be low. If the resistance is to high (open wire) the secondary voltage will be very high. Since this voltage is induced back into the primary, the ignition moduel sees this induced voltage also. This is what gets the moduels. Is adding a resistor plug enough resistance to make the voltage go high enough to damage the moduel? I don't know. I didn't design it. I do know, always use what the designers say to use.
When I first got my 500SEL, it had been used as a parts car and many things were missing. One thing was the ign moduel. I had on hand an MSD ignition moduel and used it to save a little money until iI knew of I could get the car running and it ran great. The first time I replaced the plugs, I ordered NGK plugs for an 84 500 SEL and I got resistor plugs(BP5RES). The engine started missing at idle. I found some NGK plugs with out resistor(BP5ES), installed them and the engine was again smooth as silk. On a bet I put a set of Bosch Plat plugs in and performance went down hill from the start. I took the car to the dude that make the bet with me. He drove the car, we reinstalled the used BP5ES plugs back in and the car ran smooth as silk again. Easyest $100 I ever made. Now all of this was with the MSD ignition which is capable of jumping about 3/4 inch with multible sparks/firing. So the above tells me that something about the resistor plugs makes a difference and the plat plugs are useless in our engins.
The above are my obsavations, your mileage may vary.

__________________
84 500 SEL (307,xxx miles)

I just went to a mercedes benz dealership, The mercedes dealership on Steven's Creek in San Jose, and my car originally had H7DCO's and when I went there I gave them my car info and they had required the H9DCO's. I'm gonna go with the dealer info on this one because I don't know my car's history. I have 91 300E 2.6

Please read post #1.

The coil is cheap, and should be replaced every ten years = I don't care about it...

The ignition control module is at risk...

__________________
ASE Master Mechanic
https://whunter.carrd.co/

Prototype R&D/testing:
Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician.
Noise Vibration and Harshness (NVH).
Dynamometer.
Heat exchanger durability.
HV-A/C Climate Control.
Vehicle build.
Fleet Durability
Technical Quality Auditor.
Automotive Technical Writer

1985 300SD
1983 300D
2003 Volvo V70

https://www.boldegoist.com/

Ouch,

Still its getting so hard to find non resistor plugs

I think I;m OK
Got non resistor the last 9 they had
NGK BP5ES which is one hotter than the equiv BP6ES that my engine
was spec at when new

Bosch W7D...no C on mine its a Euro

So I'm ok on plugs

What about the wires?

Problem is now they have Bosch wires & we don't know how the resistance of the new type wires in combination with the spec plugs will be off & possibly dangerous to the system.

It has been said the resistance in the new wires is lower than the oem solid core copper. Copper core has more resistance by nature than the new Bosch replacments & they don't use copper core now as it messes with the radio magnetic fields & hence the computer systems vital to the newer cars.

So even if you get the non resistor plugs
what about the new ignition wires & how does this affect the system?

__________________


83 500 SEC Euro 198K

Even although I am sure your experience says this and we should take note, I would still like to know WHY resistor plugs will cause an ignition module to fail.

I would also like to know more about wire/plug combinations. Bosch, who are not new at this game, say that we should use non-resistor wires 09097 and resistor plugs WR7DC+ on our early 107,s or other M117 powered cars.

Are they wrong? I have called them and the confirm their recommendation. It's hard to know who we should believe.

__________________
Graham
85 300D,72 350SL, 98 E320, Outback 2.5