Check engine light stays on now after new plugs.

[adjuster]

Okay, I pulled the OEM 4 ground strap plugs, with what appears to be the indicated miles on the Odometer of just under 75,000 miles. They were all coated with light brown soot, one has some blistered soot build up, that appears started to flake off, but no oil or signs of detonation.

I replaced them with Autolite Iridium plugs, that also have a small platinum pad on the single ground strap.

Noticed that one of the coil packs did not look like the others, and appears older than the other 7. Same type however, 4 pin, and this is a 2001 S8 with the 40V 4.2V8. (USDM.)

So, it started up fine, slight miss for a moment, then smoothed right out. Took it for a drive, and it ran fine, punched it, and the engine light flashed.. (It's done this before, but only when I'm pushing the car past 120mph for extended periods of time. flashes, but then stops when I slow down to under 120mph... )

Well, this time, about 80mph, it flashed like before, and now has stayed on.

I have replaced some of the vac lines with the woven cover, as they were cracked and while not leaking, crumbled on contact with my hands/fingers, and failed when I removed it from the fittings.

Question is, are these plugs a bad idea? I'm reading here that most folks use the OEM plug, with the 4 ground straps and large electrode. I have never had issues with irridium plugs before this, and on all the other vehicles I've used them, they work great.

I'm going to change out the rest of the vac lines. (I need to buy some more hose, I used what I had in the garage to replace the lines that looked the worst.)

I don't have a VAG Comm yet, but am looking to buy one. Where is the best place to get one in the USA?

Thanks, and sorry for so many questions.

[ainarssems]

So it is misfiring at high speed/load. Only thing I can recommend before getting diagnostics cable is to change fuel filter. Cannot promise that it will solve the problem but at it's inexpensive, easy to do and at least will rule it out if does not solve a problem.

[adjuster]

Interesting that you say fuel, as I noticed when I was test driving the car, that is was pinging/knocking at light loads, but did not when I floored it.

The previous owner could not tell me when he last put fuel in the S8, so I figured it was pretty old, and CA has some pretty lousy fuel anyway, especially in the LA area. (Various blends, formulations etc.)

I noticed as I drove the S8 back from Orange County, California, to Boise, Idaho that the car just ran better and better as the old fuel was burned off, and new fresh, high octane fuel replaced it.

The ping/knock is totally gone.

I'll have to change the filter, as you say it's easy.. It must be under a cover, as I don't see it? (I'll do a search.)

On the idle/smoothness and check engine light, it's gone off! And the engine runs smoother than ever, no misses, etc.

Not sure what's up, but the cruise control is working, the engine runs great, and I think it just needed to be driven, and used.

Clearly was not happy to be sitting around most of the time

Next are fuel and air filters, the last few vac lines/hoses and deciding if I can live with this tempermental RNS d radio, or if I want to attempt going to the RNS e, or just get a simple unit that plays radio and CDs and nothing else. (The indash 6 disk changer is what I've looked at.)

[S4Phil]

I'd be firing up VAGCOm before going any further with the diagnosis, it will give you a much better idea of the problem. Post up the results

[adjuster]

VAGCom is on order, should be here any time now.

I'm reading these posts about burning oil...

When I bought it, pulled the dip stick, it was wet, oil looked clean, did not have a rag to wipe the stick with, so put it back in...

Bought the car, stopped to fill up with gas, and while pumping the gas, checked the oil with a paper towel.. Yikes, the oil level was low, the gas station had a few empty service bays, and they would do the oil change for 90.00 with 8 quarts of synthentic, and a new filter... Went for it.

Did not check oil level when they were done. (Took their word that it was filled up with 8 quarts of synthetic.)

Hours later, when I stopped to re-fuel again, in about 400 miles, checked the oil, and dang it! It was low again! (Or they never filled it up all the way? Don't know, as I did not check.)

So, added oil, checked again the next day, and it was lower again. Clearly it's burning oil. Bought some more oil, and by this point, in two tanks of gas, had to add over 3 quarts of oil... Not a good sign.

On my third tank of gas, checked the oil, and was ready to add some, but found it was no longer low, and had not moved since I'd checked it last, in the middle of burning off fuel tank fill #2.

Have checked it since, still not lower, no leaks, no oil in the exhaust, and when I pulled the plugs, none of them had oil on them.

Only think I can figure is the prior owner never changed the oil much, or drove the car much, and the oil control rings gummed up? Or it was low when I first checked it, low when I filled up for the first time, and the shop short filled me. I filled it up slightly more than it calls for on the second tank of fuel, and now it's holding at that slightly fuller than it should be mark still. (Just touching the second plastic part over the "full" hashmark area.)

No signs of it burning oil, no smoke on start up, no smoke when getting on the gas after going down a hill, so I'm not sure what happened.

Perhaps the rings were gummed up, the new oil cleaned that up, and now it's running well?

The prior owner had the cats replaced. They are brand new, and it appears the O2 sensors were replaced as well. If he had stuck oil rings, that would make sense, but the plugs not being wet show it's no longer burning oil there anymore.

As I said prior, the plugs look original, and have some blistered, cracked coatings on the insulator for one plug. One was loose too, and had carbon blown up all around it, and into the plug well. (I could hear the exhaust leak, but thought it was the manifold.)

The exhaust leak is gone now, I have the Irridium plugs in there, and it's working great. I did use anti-sieze, and I'm reading that is a no-no on this motor? Why not use it? Anway, I'm looking forward to the VagCom, and what codes this engine has thrown since it was last re-set.