Update on Spark Plugs and Gasoline, related to Random Misfire

[desperado]

MIL light has come on twice now due to brief Cylinder Misfire. Never felt it, but the computer knows all. Dealer says the 420 hp 4.2L in RS4/R8 is very hard on spark plugs. My 2009 and another 2008 are both at dealer right now for the same problem; they are being evaluated by regional Audi rep to determine course of action.

The spark plugs appear to be a hybrid fine wire plug, probably iridium or platinum, with a configuration of three ground electrodes: two fine on the sides and one conventional massive above. It's hard to see how they could be fouled enough to misfire...

I found a little more information on the special hybrid spark plugs fitted to the R8. Despite NGK's claims, it appears they do not completely "solve the carbon fouling problems associated with direct injection engines"!

You can see the three ground electrodes clearly in this picture (zoom in if necessary, it's a hi-res image).

NGK says this about their hybrid design, "If carbon deposits prevent the spark from firing at the primary ground electrode then the spark will travel across the insulator to one of the secondary electrodes and burn off the carbon deposit until sparking takes place again at the primary electrode, so guaranteeing reliable ignition."

All eight of the plugs from my car showed distinct firing traces across the nose of the insulator to both of the side electrodes. Given the misfiring problems others and I have experienced, and the amount of attention Audi's given to our situation, it seems some form of fouling continues to be of concern in this engine, even though the plugs looked pretty clean to me.

I use only Top Tier national-brand gasoline in the car. Perhaps in the R8 this is not enough. "Conditions [caused by poor quality fuel] may be severe enough to illuminate the MIL in conjunction with storage in the ECM data memory of DTCs for misfire and/or lean fuel system." - TSB 00-07-09. These are exactly the problem descriptions Audi wanted the dealer to evaluate on my car.

I understand Super Premium is available in Europe; it's typically not in the US. I'm considering occasional prophylactic use of the Audi fuel additive G 001 700 03 per this TSB, which also lists the approved Top Tier gasoline providers.

[bz888]

Update. My R8 was COLD idling very rough. Nearly stalling. Never did this before. Went to Audi dealer. Replaced plugs. All good now!!

PS: I had to pay for them!

[desperado]

I'm considering occasional prophylactic use of the Audi fuel additive G 001 700 03 per this TSB, which also lists the approved Top Tier gasoline providers.

Sounds like you might have picked up some bad gasoline somewhere. I never did get any of the additive to try. Hmmm... I wonder if using it when the problem started might have saved you the expense of a set of plugs? I suspect they were not inexpensive!

[harrison]

My dealer said yesterday that plugs don't need to be changed till15K. Check engine light had been triggered by misfire/cheap gas. I have been using Chevron exclusively (premium,of course).Dealer recommended 76,Shell or Mobil. Now I will be burning 76.

[desperado]

When I was having my misfire problems I had also been running Chevron premium exclusively. Now using mostly 76, but still Chevron occasionally. They guy where I buy my VP racing gas feels there isn't much difference between the brands of Top Tier premium gas; he thinks they are all equally 'dirty' (whatever that means).

[harrison]

I ran Chevron (WITH TECHRON!) exclusively also with no problems.It was after I used an offbrand (In desert emergency)that I had a little misfiring problem. A 40 degree morning .Cold for me but not to say for the U.K..Anyways I needed to get over to dealer anyways for 5 THOUSAND mi. service.Dealer said to use 76,Mobile, orShell. Ithink I will continue to use Chevron in my older cars and switch to 76 exclusively.Till I go out of town then Shell or Mobil. Mobil claims to be a detergent gas. Better for older cars? I know that fuel can be a pretty complicated subject. I did appreciate the different fuels available in Europe. Octanes is also another long subject.Good luck !