300E spark plug wires
 

Hi,

I'm a little confused on the igition wire setup. How do I tell if I have original oem ones or aftermarket. 105k with no service history available.

I see posts that original ones are all metal. Like a metal rod? hard not flexible? How do you identify oem.

Mine appear like a regular spark plug wire (flexible in the loop from the head to the plug) but have a metal sleeve around the boot of the plug. How do I tell what brand they are?

One of the wires has an occasionally arc at the boot area which causes a miss. So it seems I should get new wires but not sure what to order. With one arcing, I'm hesitant to pry off and see what plugs I have and whether there are any of those resistor ends I see in other posts for fear old wires may break more and leave me stranded again!

Car was stuck all last week due my tumbler, had some luck and got key to turn, phew!

Thanks, Jeff

pull one out, (twist and pull at metal part, be careful not to rip rubber boot) it should have the brand stamped on the metal boot. Mine looked like they'd been in there for a long time (probably originals, the wires were hard and burnt in places) and they were Bosch.

I just replaced them with a new Bosch set. Pretty easy though routing the wires through the plastic cover on top on the engine was a pain in the arse.

you can get new wires at a pretty reasonable price (they will still be much more than for a domestic car) on ebay, or from **************.com, fastlane, or benzbin.com. I would get Bosch or Beru (both are German OEM to Mercedes) brands. The wires are supposed to be flexible; they have to be so they can be routed correctly. You may want to get new upper and lower wire holders also because if they are old they will tend to break when you take them apart.

Thanks,

I guess the other thing I'm wondering is whether I have these resistor tips that I see in some posts talking about spark plug wires.

You guys that used the bosch sets, do you have these resistor tips also? Or is it just for original MB wires? What plugs did you use with your bosch wires? Is it like this arrangement.

orig

solid wire- resistor tip- non resistor plug

aftermarket

wire- no resistor tip- resistor plug?

sorry ,still confused, partly due to not having ventured to take my wire and plug out yet.

Thanks, Jeff

take a plug out- you may be glad you did. Mine looked like they hadn't been changed for ages.

I replaced with Bosch coppers which are OEM. Don't use the platinum plugs.

If you pull one plug wire off a spark plug and look at the metal end, you should see (among other things) a marking indicating what the resistor value of the wire end is. On my M103, it's indicates 1k ohm. I have a Beru wire set on Bosch copper core plugs. Get them from Fastlane here and you shouldn't have to worry about it too much.

Jeff, I expect that your wires are Beru since they have the metal sleeve around the rubber boot. As far as I know the Bosch wires lack the metal sleeve. The original wires on our 1991 300CE had a small red ID tag (1 thru 6) on each wire to identify which plug it went to. Note that there are similar markings (1 thru 6) on the distributor cap and the valve cover ... making it as foolproof as possible. The Beru replacement wires lack the small ID tags so you have to match the lengths of the new wires with the old ones.

As for spark plugs the Owner's manual specs Bosch H9DC0, Beru 14K-9DU0 and Champion S12YCC ... all should be copper plugs. Recently when I tried to buy Bosch F9DC0 plugs for our 1991 300CE both the local MB dealer and an online website called out a Bosch F8DC4 instead. The dealer explained that the Bosch F8DC4 performs better in that vintage engine. Note that the F8DC4 has a square seat and a gasket while the H9DC0 has a tapered seat without a gasket. If a torque wrench is not available, hand tighten the plug until it is seated in the cylinder head. Spark plugs with gaskets should be tightened an additional 90°. Spark plugs with tapered seats should be tightened an additional 15°.

Thanks guys,

Ferdman, Yes I have a very small metal sleeve around the boot so it sounds like I got beru.
Do I have seperate resistor ends also?

If so, I got a wire arcing at the boot to the cylinder head, is it the wire or the resistor end that needs replacing or both?

How do you tell which is bad? I'll replace whats needed but if something is good,theres no sense.

Thanks, Jeff

Jeff, I'd bet that the ignition wires are original. With 105,000 miles and 12 years old I'd replace them (the entire wire and ends) along with the distributor cap, distributor rotor and spark plugs. Obviously check the condition of the distributor cap and rotor before arbitrarily replacing them; but, it's likely they are original too.