SicilianStyle

Hi MBWorld,

I have a 2006 C350 with the M272 3.5L V6 engine that I was looking to do a tune up for. I plan on changing the spark plugs, ignition coils (they've been the same ones for the last 4 years I've owned the car), new air filters, MAF cleaning, and an oil change.

I know the owners manual recommends the Bosch/NGK Platinum spark plugs, but is there any issue with upgrading to Iridium plugs? I say "upgrade" because it's my understanding that Iridium plugs have better performance and a more complete combustion. I assume this would translate into slightly better fuel economy and power. I've driven myself absolutely neurotic researching about this for hours upon hours, but it seems there's not too much information regarding the application of Iridium spark plugs in our M272 engines.

There are my options:

1. (OEM): NGK 4288 PLKR7A Laser Platinum
2. NGK 93911 LKR7AIX Iridium IX
3. Denso 5353 IXUH22 Iridium (These are boasted as being 'performance' spark plugs, having the .4mm center electrode)

I also note that the Laser Platinum plugs have a resistance of 1000 ohms vs. the Iridiums which have a resistance of 5000 ohms. Does this matter at all?

Thanks so much for the help.

tjts1

Yes the resistance matters.

SicilianStyle

In what way? Will they mess with the ignition coils or throw off the ECU?

tjts1

Resistors in spark plugs exist to block ignition noise from messing with the car's electronics. To little resistance and you'll run into weird electronic symptoms like noise on the radio or even stalling. Too much resistance and your coils might not be powerful enough to fire the plugs causing misfires, loss of power at high load and CEL. The coils were designed to work with a specific plug. Use that plug. Just because a different plug is more expensive of promises some kind of ill defined performance improvement doesn't make it an upgrade.

SicilianStyle

Hmm.. I had a feeling this would be the case. HOWEVER, upon a little bit more research, I've found that the 2 OEM spark plugs had 2 drastically different resistances. The OEM Bosch Platinum spark plugs have a resistance of 6000 ohms, and the OEM NGK Platinum spark plugs have a resistance of 1000 ohms. Now I'm even more confused...

Stevebfl

Do not use the general platinum plug. Use the one that is the original equipment plug usually Bosch. The gimmick platinums will cost half as much as the true plug. MB also recommends phasing the plugs. That means that the electrode must be pointed the proper direction within the cylinder. Coils don’t need replacing till they fail. They do not have a planned maintenance cycle. The plugs are recommended to be replaced every 60,000 miles or five years. Don’t waste your money. You can not get any better performance than with the OE plug.

Donald McPherso

Just change like for like. I bet the difference would be so negligible you would never notice.