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I just wanted to share what seems to be yet another spark plug success story. To make a long story short, when I bought my car it had Bosch Platinum HR9DPX's. I ordered one of those $300 (Wire, Cap, Rotor Plug) tune-up kits about a year ago assuming that they knew what was best.
Last week I noticed a horrible hesitation and could tell right away some of the cylinders were "missing". I have dealt with the annoying uneven idle from day one but this hesitation that developed out of the blue was far worst. When I pulled the plugs (Bosch Super HR9DC's that were supplied with the tune-up kit) I was completely floored.
They were all caked with a white crusty buildup, I was amazed that my M103 was even firing!! I also noticed that the ceramic insulators around the electrode were ALL cracked and must have disappeared a long while ago into my poor cylinders. I immediately recalled reading about non-resistor spark plugs and did some further research. RBYCC seemed to swear by the NGK BP6EFS from Europe and now I know why.
I put them in after work and to put it simply, I have NEVER heard my engine sound and feel so smooth. I have yet to open her up on the highway but I am so very pleased with the result.
Any set of non-resistor plugs within the right temperature range should make a huge difference if you are currently running resistor plugs. I will however warn you that they are almost impossible to find in the states. I spent a whole day visiting various parts places (Napa, B&B Performance, etc) and they all told me that they are almost nonexistent here. I could post the Ebay seller that I bought them from if you like.
If you do a Google search you can find the same seller in which Ed (RBYCC) recommended in a post somewhere in the MB forums community.
I'll have to order a set for the heck of it for the wagon.
This website: www.clubplug.net has most if not all of the NGK plugs. They also have the Denso plugs. A Denso T20EP-U is virtually the same as a NGK BP6EFS. I noted that they didn't list NGK BP6 EFS specifically. There are several varieties of BP6EF, tho. I have a query in at another forum to try and find out which NGK plug they offer is correct. Prices are very reasonable, $2.14 each for most of the NGKs and $1.74 each for most of the Denso plugs. If anyone has another source for these - or a recommendation for which of the ones listed at the website above is right, I'd appreciate knowing that.
Last edited by jshumphrey; 08-18-2014 at 07:32 PM.
Reason: Adding a question
Bosch platinum-ir fusions are non-resistor and the iridium-alloy has the benefits of platinum for longevity and iridium for performance, plus having raced a 250bhp i6 before my gut just plain loved the four prongs.
When I took out the NGK that was in the 2.6 and put these in, it didn't lose as much speed up the same hills and economy improved slightly, levelling at 30mpg from about 28.
I love these plugs.
Now they're in the 3.0 with a cam, easily a 200hp motor with terrific throttle response. I will switch to cooler versions, but that's because I'm shaving the head, plugs are really interchangeable between any M103 (along with just about everything else). Pretty sure they list cooler plugs on the W124 purely because it tends to sit in traffic longer with the aircon on.
I have a pretty good gut for tuning, learned it doing triple SU carbs by ear on the race motor. Other bosch plugs might be crap, I wouldn't touch the resistor straight platinums for an old Benz, but these iridium alloy ones (despite platinum being part of the alloy) are good plugs.
07-06-2009, 06:52 PM
