NORCAL 4.2 A6

but I am trying to find someone who has changed plugs on a 4.2. Curious if it's tough or just PITA? Searched for best plugs and a lot have recommended BOSCH, just not sure on part#. What's everyone using? TIA

MP4.2+6.0

Maybe 60-90 minutes depending on experience, provided you know how to remove the air filter assembly (especially the four spring clips) and get the MAF connector undone. With the trim panels removed, you unbolt the brackets that hold the trim covers to the valve covers and then unplug and unbolt each coil on plug assembly--simple 10mm bolt stuff. Then you are at the plugs. You will have the air box open and out, so change the filter at the same time if at all dirty/used.

All this assumes you don't run into any other issues like a valve cover oil leak or bad vacuum lines. Good time to inspect all that.

Plugs, I switched to NGK's from Bosch on Audi's 15 years ago. NGK is often Audi OEM now, and I don't view Bosch as an innovator. In practice, motors run so clean now plugs are very seldom clearly differentiated. 15 years ago with CIS injection or carbs I could see more fouling on Bosch's than NGK's; NGK was much earlier to a copper core for example.

Two quality NGK platinum multielectrode plugs are available for the 4.2 motor. The later one (6872) does not have grooves on the porcelin, the earlier one (3199) does. Removing the grooves was only to avoid the plug wire/coil from getting stuck. I haven't seen any issue there so I stick with the original NGK plug for the car. The good platinum ones are multielectrode, which extend life and also keep the electrode better positioned to launch the flame front. I'm not an Iridium fan, which are really geared to longer total wear life (the 100K mile type stuff) than performance. ecs tuning carries both types of plugs, or you can go to ngk.com. That is NOT NGK's web site, but rather an online buying site. They have good catalog info and pictures of the actual plugs--including the Iridiums, more basic platinum and even the older copper core and V groove options.

NORCAL 4.2 A6

A later model than mine? I have 2001 and ran that part number, but doesn't come up for my year. Would these be the same BKR6EQUP?

MP4.2+6.0

...EQUP is is the 3199 plug.

...EQUA is the 6872 plug.

If you go to either the ngk factory site or the ngk.com site, you can see the shorter four digit numbers that are used in the trade and on their packages. ecs lists them by the long number you have.

Break point on the plugs was starting with 2003 4.2's when they cut to 6872s (BKR6EQUA)

MP4.2+6.0

<ul><li><a href="http://www.ngk.com/results_fitment.asp?pid=3199">3199 applications</a></li></ul>

MP4.2+6.0

<ul><li><a href="http://www.ngk.com/results_fitment.asp?pid=6872">6872</a></li></ul>

audikillsbmw

And to answer your other question, I put in NGK's.

NORCAL 4.2 A6

the Iridium as a premium class and the multi gound as super class. Last question are you recommending not to go with the Iridiums?

MP4.2+6.0

Short version: Good enough for Audi OEM on a high HP/ltr. NA motor, good enough for me.

Long version:

Iridiums cost more in general, but per my original post their real selling point is longer wear cycles. Car manufacturers spec'ing 100,000 mile changes now often use Iridiums, though some Platinums are spec'ed for that too.

Iridium doesn't conduct as well as Platinum (which in turn doesn't conduct as well as copper or silver). Iridiums also do not come in the multi electrode design. Multielectrode helps offset the wear factor, and performance wise doesn't put the electrode in the way of the ignition flame front like a single electrode plug. An old tuner trick (called indexing) involves pointing the electrode gap (open side) toward the intake valve--pain in the neck to actually try to do, but supposedly good for some ponies, at least on an old 2V V8 where breathing and spark may not be optimized. Moving the electrode to the side like in a multielectrode plug is arguably even better, particularly given the Audi 5V head has a very centrally located plug location. Combine better conductivity--relating to spark output--and performance characteristics of multielectrode, and I think it's the better choice. To be fair, newer plugs like Iridiums have reduced the size of the single electrode, both for cost reasons and to reduce its impact on the spark flame front.

I also want to pull my plugs every 20,000 to 30,000 miles anyway to see what is going on in the motor (deposits, oil fouling, etc.), so the +/- 30K service interval makes more sense to me on an older car where I wrench on it and will replace them once they have some miles on them. Thus longer wear life from Iridiums is something more useful to me on a newer motor (or for the manufacturer paying for service...) where I don't expect to have any issues.