plug leads....genuine or oe

[louisjames]

ok thanks all for replys, went to stealer today, they had no real suggestions. did say it was the air temp sender unit for ecu, new one was 6 quid plus vat so may aswell replace it. booked in for diag on wednesday.

anyway thought about changing plug leads, they want 32 pounds each plus vat!!! seven leads remember, thats unreal, should i buy genuine or will after market leads be ok? i know this is a sometimes a mixed bag question so would be glad of your views to help me make the decision.
thanks

 

[TVRTASMIN]

Try Magnecor for a set. Should be around £35 a set. Top quality too.
You could even have a KV85 racing set for the price of one Merc lead.

 

[kth286]

louisjames

Why seven leads ???????????

 

[louisjames]

thanks il try them, and second why 7 leads!??? umm, 6 pot engine, king lead?? makes 7 right

 

[kth286]

louisjames

Don't you have the 104 straight six engine where the coils are over the sparks plugs under a cover ????????

There are 3 coils and because each coil supplies 2 spark plugs each and sit directly into 3 plugs, there are in fact only 3 ignition cables required, all three being different lengths.

Merc usually make them up on the spot for customer needs and the cable is on a roll. The fittings are then crimped to the cables using their hand tool that is kept in parts dept.

So the cost of three leads will not hurt so much now will it ?????

Does this help and clarify matters.

 

[wireman]

I have gone diesel now but wish that all the spark ignition boys would stick to using supression type cable, many boy racers fit solid wire leads to make it go better, it wont solid wire does not suit modern engine systems and creates merry hell on other peoples radio sets, It was made illegal in the 1950's so why do folks still want it?
As an electronics chap I have spent some time in my youth testing the performance of all my cars systems and can truthfully say that solid stuff is pathetic under some conditions and no better under any other.
As to which particular type to use I would say any that looks to have mechanical integrity that will fit securely in the instalation clips etc and is of the suppresion type.

 

[louisjames]

david, yes thanks great, so i only need three leads is that right? and i think thats my engine yep. 24v straight 6. plastic cover up the middle of it.

and wireman are you saying that those magnecor leads are crap? are theysolid wire leads? if so and davids correct i will defo get dealer leads if i only need three.

 

[GSM1]

Glad your are going for OE leads,I have a 320 V6, had an issue with idle and the garage I bought it from put on a set of euro car parts leads, they were like the cord from a kettle, very far from the quality of merc leads, took it back and they took a set from a ML 320 to fit on mine which I was pleased with , still have the idle issue though

 

[124coupe]

You should also bear in mind that any misfire is far more likely to be caused by the 3 "boots" under the coils than it is by the 3 wires t the other plugs. As they live in the hot hole under the coil they degrade over 2-3 years or so.

The boots are about £6-7 each from the stealer.

What are the symptoms you are trying to fix?

 

[GSM1]

The car doesn't misfire, when you sit stationary it rubbles slightly, not terrible but one of those things that annoys me, performance is fine, they told me they took all the coil packs from the ML and put them on my car but i'll have to take their word for that, it was same year but had only done 29k compared to my 70k

 

[jberks]

The car doesn't misfire, when you sit stationary it rubbles slightly, not terrible but one of those things that annoys me, performance is fine, they told me they took all the coil packs from the ML and put them on my car but i'll have to take their word for that, it was same year but had only done 29k compared to my 70k

Been there- twice. Damn anoying on the sweet V6. It was plug leads on my E240. Actually it was the supressor caps to be precise. Same symptoms on 2 occasions. New set cured it both times. On the first set, corrosion was visible inside the supressor caps too. Not so much the 2nd time, but the new set still did the trick. My experience is that a set of leads lasted 3 yrs before playing up (happened at 24k and 60k) so if the set from the ML is over say 2 years, they may be no better. Assuming the plugs have been done, I'd still go for a new set. It's such a common problem, I had a hell of a job getting a diagnosis as every mechanic I spoke to said "they all do that sir".
Yes they are damned expensive for what they are. Worse still, remember, there are 12 of them. From memory it cost me £250 a time, but it did solve the idle rumble.

 

[louisjames]

ok, looks like im going genuine then, thanks for the help guys!

 

[wireman]

I do not have any brand specific details of ignition leads, but since the 1950's the law has stated that any spark ignition engine must have radio suppresion fitted. The reason is simple all electric spark discharges emit broad band radio signals and these cause problems for the users of radio systems in all walks of life. As a result of the law change ignition system manufacurers developed leads coils and plugs which conform to the legislative requirements for EMI suppression, this includes resistive HT leads which act to reduce the peak spark current (to around 1 ampere) and thus reduce the impulse of magnetism around the leads as the spark initiates this will effectively kill off any chances of the ignition system becoming an inadvertent radio transmitter. To accomodate the characteristics of the HT leads the coil also has different electrical properties to those used on pre legislation systems, further changes have also been undertaken with the advent of elegant electronic ignition systems.
Using plain old solid HT leads with a modern coil will result in fundamental changes to the operating characteristics of the whole system some of which may be damaging to the semiconductor sub assemblies in the vehicle, the worst damage in my opinion is to the radio spectrum where impuse interference pitter patters all the way through your desired radio programme just because some ill educated oaf wants to be clever and mess with a highly refined electronic design just because they have heard that solid wire is better than that wet string stuff they fit today.
The characteristic which is changed the most by using different resistance value leads is the Discarge time constant which is defined numericaly by divding the coils secondary inductance by the total load circuit resistance, typicaly 100-2000 ohms for the coil plus 1 ohm for solid wire and 25,000 ohms per foot for carbon suppression types. This has a huge impact on spark duration and the available energy in the spark, the higher resistance leads give a shorter dischage time constant which is beter matched to the ignition requirements of the fuel.
The misinformation that soild HT lead is good stuff allows some after market vendors to get good money off lots of folks who want to improve on standard kit.
There are some ignition systems designed for special purposes which do use solid wire leads but other and much more expensive radio interference measures are utilised in these systems
The early rubber and then PVC insulated suppression cables used to go soft and spongy or hard and brittle resulting in failiure rates which were higher than the older cables showed, in addtion the resistive core was built of conductive particles and a piece of plastics cord which also had poor life expectancy. This gave the modern leads a bad reputation.
The current generation of leads still suffer from life expectancy problems, (just like solid ones did) but they are much better than they were and you should replace them with similar along with any other ageing prone HT parts ie dizzy cap and rotor arm if your engine has them after a few years of use or the first sign of trouble.
I do not expect to have my radio reception compromised by a Mercedes, and to date it hasn't been, it seems that small ford and vauxhall owners are the worst EMC offenders in the que at the lights which we all seem to have to join these days.

I very much doubt that the nice looking high class after market lead sets are crap as you seem to think I inferred its just that in consideration of my experiences of modifing engines and developing my own versions of both inductive and capacitive discharge ignition systems they most likley wont make a jot of improvement to the engines performance and may make it worse or less green.
You dont have to pay a fortune for your new HT leads just make sure that they are of similar chracteristics to the tired old ones.

I'll use the wet string stuff any time but I aint gona change the handle to wetstringman.

 

[TVRTASMIN]

david, yes thanks great, so i only need three leads is that right? and i think thats my engine yep. 24v straight 6. plastic cover up the middle of it.

and wireman are you saying that those magnecor leads are crap? are theysolid wire leads? if so and davids correct i will defo get dealer leads if i only need three.

Nothing wrong with Magnecor leads and they ARE suppressed and conform to current requirements.
They even have a 10 year no quibble guarantee!

If you try to use a solid copper core style lead on a car equipped with an ECU (most cars since mid 80's) then the interference would cause serious problems, not just for your radio.

Personally i've never heard of anybody using solid wire to make up there own leads.

 

[Big Ian]

Leads

I've used Magnecor leads on my wifes MR2 and the difference was incredible considering it was a cheap and easy job to undertake yourself.Acceleration / sharpness improved along with smoother tick over.

 

[Flying Scot]

I've used Magnecor leads on my wifes MR2 and the difference was incredible considering it was a cheap and easy job to undertake yourself.Acceleration / sharpness improved along with smoother tick over.

how silly you are confusing the practical with the theoretical you were obviously knufoosed or drunk :mrgreen:

 

[cassie41]

What make of Spark Plugs do Mercedes genuinenly use, which would not affect a warranty? I have an A200

 

[Steve@Avantgarde]

Bosch or Champion usually.