S8ilver

Silverd2,

Which Bosch part number are you using/have you used? I'm about due for a set of plugs on my '02 S8 and have come across many different part numbers. I heard mixed reviews on NGK, just tossing that one in as an alternative. My last BMW had NGK as an "OEM replacement option."

Bosch 7406 (FGR7KQE0)gasket seat
Bosch 4417 (FGR7DQP)
Bosch 4457 (HGR7DQP)
Bosch 7411 (HGR7KQC) taper seat and 1.45mm shorter than 7406

NGK 3199

http://www.ecstuning.com/Audi-D2_S8-...n/Spark_Plugs/

http://forums.subdriven.com/showthre...g-7406-or-4417

audinutt

I revamped my stereo in my 2001 A8L.. I gutted the bose speakers and amps, replaced with Mcintosh components and a Mcintosh Amplifier. I also have a sub installed.

All of this is running off an RNS-E unit and the sound quality is fantastic.
It makes the Bose sound like garbage (which IMO it is)

-Richard

silverd2

You can't use the 4457 or 7411...they both have tapered seats, which can't be used on 40V engines. Tapered seats (with no gasket) are used on 32V engines (97-99) which are machined differently to require those. 40V engines are machined flat to take flat seat gasketed plugs.

The 7406 is the OEM thick copper core plug, with 4 prongs.

The 4417 is the platinum +4 plug I use (flat seat for 40V)...I find them smoother and more powerful at high rpms...slightly cooler burning plug, which is always better for high rpms.

Hotter plugs (7406) tend to be a hair (almost undetectable) more responsive at low rpm, but suffer a little at high rpms..."rougher" and less willing at redline.
Platinums (4417) tend to have a smoother idle, less vibration throughout the rpm range and love the high end.

jluehrs

I had that problem with my S8 Bj. 98. Both cats were melted and destroyed inside so that they were blocked at higher rpm.

The outcome was no power and random misfire.

I hit under the cat with a hamme and there was rumbling noise inside.

Bye Jens

Adjuster

The cats appear newer than the rest of the exhaust, and the prior owner mentioned that he's had them changed, and new O2's before and aft of the cats.

I put the stock plugs back in after giving them a quick aluminum oxide blast to clean them up and the Iridiums came out clean as a whistle. Amazingly clean in fact.

I think the 5 gallons of toulene I added to the fuel must have broken loose some crap, and that combined with the plug change resulted in the misfires. Now nearly 3 tanks of fuel later, the CEL will only flash when I WOT for an extended time, but stays lit all the time. (I have a VAG Com, and have cleared the codes, but need to do it again.)

My plan is to change the fuel filter next, keep running without the toulene in the fuel, and see if it goes back to how it was. I will change over to the Platinum +4 plugs in the future too.

AS for the stereo, do you remember what size speakers you used? I'm very tempted to "gut" the stock Bose speakers/amps, and replace them with same sized high quality ones in the Bose housings, and locations. I don't think I'll need a sub, as I get plenty of bass now, and this removes the RNSd and 6 disk changer from the car, but upgrades me to iPod/phone/bluetooth calls etc. I don't need nav, but will retain the stock nav in the cup holder...

Adjuster

UPDATE:

So, I've run just pump premium gas, and it's not any better. I decided to try some more Toulene, and since I have quite a bit, figured it might just clean up what's causing the problem, or it might reveal the true culprit, so I put another 5 gallons into an empty tank, and then drove over to fill up and wash the car.

Ran fine, but still flashing the CEL on WOT, or speeds over 65mph... Argh.

Ran that tank of Toulene mix through, and did another, since it seemed to be getting better, I could drive 70mph at times before it would flash...

But never improved more than that.

So, replaced the fuel filter. (Finally.) Some debris in there, and what looks like a clear/yellow gel floating around in the fuel? It's not water, that would sink in the fuel, this stuff floats barely. Cut open the filter, and found the paper media pretty dark, with more of the gel stuff in there.

Was excited to think the gel might have been the culprit, took it for a drive, and no joy. Still flashes at WOT and speeds over 65/70mph...

Just injectors and the pump to consider next. The injectors are working, they make normal noise, and the pump is not noisy, and appears to put out plenty of pressure, but I have not put a gauge on it. (The filter banjo fittings needed to be supprisingly tight to seal up, first time I put it together, and checked for leaks, it was leaking pretty quick, loosened it up slightly, sprayed fuel around quite a bit, and then cranked it down till the fittings did not weep anymore, and it's been fine ever since. (I think one of the inner gaskets was not seated fully, it was slightly larger than the machined seat, and had a burr that must have caught and prevented it from sealing up right. Some more pressure, and it dropped in tight, and sealed up fine.)

Still getting the VAG Com codes of multiple random misfires....

silverd2

No new theories on misfires, but wanna ask >>

You DID use new crush washers on those banjo fittings, didn't you?
If not, old ones will always leak (I've found...and warnings in Bentley since early VW fuel injection)...not reusable.

I've had some luck (when I had to), by coating (thin) old ones with black RTV, allowing partial setting, then cranking down and waiting till full set before pressurizing system.

Adjuster

Yes, brand new, brass crush washers that came with the WIX brand filter.

The aluminum body of the filter had the seats cut, but the out side, the bigger fitting, had a barb, and it did not seat fully until I really put some force on the banjo bolt.

I've done many motorcycle brakes and other fittings like this, and always use new washers, and don't over tourqe them, as banjo bolts are weak, just how they are designed. (Hollow with a hole drilled through the body of the bolt... Too much tourqe, and they can twist and fail at the drilled hole.)

I have not put them back in, but I checked the gap on the Autolite "Pre-gapped" plugs that I was not supposed to gap.. LOL It ranged from over .40 to nearly .45 with the feeler gauges.. So I re-gapped them all to .30 and will perhaps put them back in the engine today. What is the stock gap called out for? (Or is there none, as the stock plug is that air gap/4 prong surface fire stuff that you can't gap the plugs?)

In my turbo engine days, any gap over about .28 on a high boost engine would blow out the spark, and create misfires at WOT/boosted conditions, and I got the best performance at .28 with the Supra engines, but stock they called for a wider gap, but stock only had about 8 to 12 psi of boost too. (Most of mine were 18 to 21 psi or more depending on the build.)

I have a new fan clutch on the way, this one is shot, and the temp will climb if the car is sitting still for awhile with the AC on, and ambiant air temps over 90f. (Okay, it's only mostly shot, but failing, so time to replace it.) Added some Redline Water Wetter, and it take WAY longer to get the needle to move hotter now, so that's good, but still it moves, and a fan clutch is cheap to cure the problem.

I figure I'll change the serpentine belt out while I have the fan off, and it looks like I can do all this from the top, just pull the air intake and fan bezel ring, and then turn the fan off the drive pully right? (And use a breaker bar to de-tension the belt, replace it, and put the new fan back on...etc.)

Any tips for this job that make it simple? (I see the one about using the hole at the tensioner to lock it "loose" and put the belt on, then remove the pin/bolt/allen wrench and tension the belt back up.)

If I could just get this flashing CEL, and the drop out of injectors as a result, this car would be in great shape. (It resets as soon as it's turned off and back on, but that's a chore I'd rather not have to do every time I get off the freeway, and back to lower road speeds around town where it does not cause any issues at all.)

silverd2

I stick to 4 prong plugs on my car...I really like em. I've gone back and forth between OEM Bosch (thick...copper?..center electrode) and Bosch platinum plus-4's, which I'm currently using. The OEM seem to burn hotter...good off the line, but not as "pleasant" at high rpm. Platinum's seem to maintain their heat range throughout the rpm range....smooth, strong and vibration-free all the way to redline.
Ever since my 1st 4-valve motor (Scirocco), I have not liked the feel or behavior of ANY single prong plugs. The Scirocco was the 1st car I owned that came with factory multi-prong plugs...and after some experimenting, I understood why. I played with different type plugs with my last 3 928's also...always went back to 4-prongs. Haven't even tried anything else with my D2...I feel no need...perfect match for me.

Yep, during this 100 plus heat wave, I've noticed that my clutch fan is less than adequate in traffic...it used to stiffen up nicely in the heat, but now it's a little too easy to stop...doesn't full in the CFM's like it used to. That's in my near future, too.

I've had my fan out several times for other reasons....not hard to do with the right tools...slips out with the fan ring. Don't know if the reverse threading on the fan does it, but it seems to tighten itself over time...always an effort to break it loose. I use tools similar to the drawing...I already had a thin 32mm wrench in my bicycle tools and bought a cheap pin tool on eBay. I found breaking the nut loose is easy if I position the 2 tools close enough to get my biggest channel locks (wide open) around both tools and pull em together...pops it loose easily every time...same for replacing it.

I remove/replace the serp belt as you described...open end wrench on the tensioner, then plug in an allen wrench (or similar)...when it's detensioned enough, it will slip right in. I also remove the electric fan (3-point bayonet mount), still plugged up, for easy clearance to feed the new belt into place.

I've been VERY happy with the Dayco belt I installed...looks brand new after 20K miles. They have one (online sellers have it) with pre-cut flex grooves on the ribs and some really nice materials. Not where I bought mine, but this is it >>>

http://www.autopartswarehouse.com/sh...8_quattro.html

Viscous fan tools >>>

Adjuster

Little update on the plugs. They are WAY better now than it was, starts right up, idles smoother, and down the road, it's smoother as well, and pulls excellent v/s before that now I realize was somewhat not as smooth as it could be.

These autolite plugs have a .07 wire irridium point on the electrode, and a small platnium pad on the ground strap that's also pointed to open up the spark to as much surface area as possible. I gapped them at .30, and that seems to be a good spec over how they were shipped that was .40 or .45 nearly on some. (Most were wider than .40, and .45 slipped in there on two of them.)

I figure when I tried them out, the wide gap caused more misfires, and that was felt in operation and with the CEL light.

Putting the cleaned up stock "copper" 4 prong Bosch plugs that I assume are the original ones as this car only had 75k on it when I bought it was better, but still had random misfires, and was not as smooth as it is now under load at lower speeds.

So, the Autolites are working, but I'm still getting the CEL flashing at WOT, but the engine pulls very smooth now. Also the CEL flashes and then the ECU drops an injector or two if I run steady speeds over 65mph, or up a hill at 65mph.

The fuel filter is new, so it's either the injectors or pump, and my guess based on no pump noise, and plenty of pressure/spray from the fittings at the filter, that the injectors might be the way to go next. (I'm hoping the toulene in the fuel I'm running will clean them up, but so far, that's not been the case, but they are better than when I first started, at 45mph, the CEL would flash, and just driving around town would cause injectors to drop out by the ECU. (I'm guessing it sees a lean condition, and drops them to avoid potential lean running damage or the NOX it creates more likely, since under such low load, the lean run/burn is not going to create engine damage in my experience.)

My brother says the ECU is screwed up. If the injectors are clean, and the pump is fine, and I've found zero signs of leaking gaskets, hoses or other un-metered air into the engine, I can't say I disagree...

Any ideas? How common is a failed intake manifold gasket? And could a loose, or leaking exhaust gasket to manifold cause this problem? I've got an exhaust leak I can hear on the left side. (Drivers side of the engine.)

Any tips on the best way to tighten up the exhaust manifold bolts? Sure are lots of them, and not easy to see from above, but I can feel them...

As I've said before, the cats appear to be new OEM units. The pipes go back new with the new cats to the older cat back OEM S8 exhaust pipes. (Nice design and appears to be high quality, don't know why so many people cut them out and put noisy flowmasters on there, since I don't see anyone showing more power as a result, just more noise.)

The prior owner says the O2 sensors were replaced at the same time the cats were, and the plugs/wires/sensors do appear new, like the cats/pipes.

The engine is very strong too. That alone confuses me, if the injectors were dirty, failing or the pump was failing, it should be down on power I'd think, and it's not. I pulls like a freight train, and even the top end has power. (But I have to say, when I first go it, at 90 to 100mph, it was amazing, now it's lacking power at that speed, but gets up to 90/100 with full power... So lower fuel delivery very well could be the problem. (A vac leak should be a serious problem it idle and low engine RPM, but would be nearly nothing at 6000 RPM.)

Guess it's time to pull the injectors, or just keep running more Toulene, and hope they clean up with use... LOL