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Hello guys, my 2017 S8+ with 45k miles, no tune. The car randomly misfires mostly on cylinder 5. 2 days ago replaced spark plugs and swapped coils to check if coil is wrong. No result, still randomly misfires on cylinder 5. Old spark plugs looks the same, no difference between plugs. The car runs great, but sometimes I feel very slightly rough idle, no issues in higher rpms. Also sometimes I feel a noticeable smell from exhausts like unburn gasoline. No issues with fuel consumption, with very sensitive combined driving I can reach 23mpg. I am from central Europe and we have E10 gasoline with relative high 9% share of biocomponent. Any ideas what to check? Thank you
Old spark plugs sorted as they are in the engine when you stay in front of engine, so 5 cylinder is bottom right one:
Can you translate what the display in the second image is saying. You mention its is about misfire count. What do the actual words for each cylinder say? Over what period of time? Forever? During data run? Since last clear?
For what it is worth, I am suspicious about both the tool and the count. Arguably on the face of the data, all the cylinders have an issue to an extent, and on several others it is more pronounced. But I don't know what he "denominator" is even assuming it is a misfire count--life of car, since last data clear, for a 30 minute data run, etc.
As another reference point, gas in a lot of US states has Ethanol. Where I am in CA it is 10% for winter months and has been for a couple decades. Our gas is also the USA 91 octane premium, which is the lower end of typical European premiums. In other words, I doubt this is a fuel quality issue.
What I can say so far is there is nothing visual about the plugs that gives any clue. No obvious excessive wear; no electrode issues; dry of any obvious oil; typical gray with slight tinges of gray/light tannish color; slight dry sooty look typical of plugs on a good running motor and in right plug temperature range.
That image shows misfires for each cylinder (1 to 8 from top to bottom) during the life of car (3.5 years and 45k miles). My mechanic said that few hundreds is really small amount of misfires for this mileage, but cylinder 5 doesnt seem to be OK, also rough idle and random smell is not OK. Car has almost no oil consumption, no smoke. I would like to run car with full care with no issues, so this makes me little nervous, because 3 guys couldnt identify reason of misfires
1. Clear misfire count, do a driving run and see what you get after that.
2. I would have just replaced the coil pack, since here they are now $25 or 30 USD. Labor is more than part itself these days. With all plugs out, I would maybe have put the coil pack as far away as possible--diagonally opposite cylinder. What you/mechanic did diagnostically is typically fine on the fly/without part on hand. But then I would still really be sure the data set is now fresh again.
In terms of other areas to think about, with context that misfires also often happen if fuel fixture is too lean:
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A. Possible vacuum leak. Look especially for anything closer in to cylinder 5 physically. Given it is a known problem area for 4.0T, consider the PCV related part. Audi revised it and your S8+ is late in the model run, but I am not sure if you would have the older or newer version. I have never had to dissassemble mine, but you might check into that. In particular, where does the PCV system actually dump the oil vapor into the engine intake manifold? If it is nearest to cylinder 5, that would be a pretty strong clue. If not that part, have mechanic (or you) look for anything that attaches vacuum wise to that part of the intake near cylinder 5.
B. High pressure fuel pumps, one of each side of motor. Those do fail and folks on this board have reported them. But yours doesn't fit symptoms very well. You don't report any real running issues. Your misfires are not concentrated across one side or the other of the V and also are not more evenly across many cylinders on one side.
C. Always the (low probability) bad knock sensor scenario. The motor has several and then uses triangulation to (sort of) determine which cylinder it thinks is misfiring. But your smelling fuel suggests something is not in order. But even to that, something seems odd since fuel smell means overly rich mixture typically, while misfire usually connects to lean unless cylinder is just not firing at all. In turn when a no fire situation occurs and raw fuel is dumped to exhaust, you would maybe hear some backfiring at times if severe.
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So far it doesn't matter for plug appearance, but just to be sure we are all on same page: which cylinder are you referring to as #5? It might matter for the coil pack rotation. Different companies use different nomenclatures for this, especially on V motors. For Audi, number 5 is the front cylinder on the right side of motor as you look at it under hood/bonnet--the front of the USA/ continental Europe driver's side.
Good info and catch! Interesting, and seems on point, other than the poster didn't get into the high rev situation/experience directly. As a continuing and lower cost diagnostic, this may reinforce the idea of clearing codes/data as I was saying, and then testing for both normal driving and separately for high RPM situations.
For original poster, the TSB does seem on point. Reading that description, if it is not just the ECU software refresh it discusses but then the other engine work, that is going to get VERY expensive. Seems like a big heads up to other S8+ owners too.
The refresh work and check already means a visit to an Audi dealer service department/workshop. The TSB only provides time estimates for some of it like the actual valve spring shims, but there is no estimate provided for important and labor intensive parts like the camshaft removal, all the other removal items, readjustment, csuspension+sensors+camera alignment, etc., plus the A/C system. In plain English, it indirectly reads like a lot of the front end of the car needs disassembly to get at the camshafts while still leaving the engine and heads in the car and mostly assembled. As I recall, an Audi "time unit" (TU) is simply a minute of book estimate shop time, but many of the labor intensive steps don't have that direct estimate.
Finally, I remember you (the original poster) are not in North America, so maybe some backgrounder on how a Technical Service Bulletin (TSB) is handled here. A TSB gets issued when a recurring problem is flagged, and Audi thinks service personnel should be aware of both the problem and the fix to avoid wasting a lot of time and repair cost. It is also short of a recall and a way manufacturers can try to keep repairs both quieter and avoid covering them for the whole life of the car. The first part is good, the latter part a way companies cheap out and try to avoid paying for design or build mistakes they made. The TSB header seems to be suggesting this would be covered if either still under warranty, or at least some parts of it under the emissions warranty. Warranties are country specific, and then even within the United States the emissions related warranties vary from state to state depending on whether the car was sold under the tighter "California" rules and set of states, or the looser Federal rules. I suggest you talk to a local dealer service department, show them this USA TSB and inquire for the equivalent document in your country. Then find out what is warranty covered, or not.
This cylinder 5 misfire its an common issue on 4.0T . I have a 2013 S8 stage 3 ( +4mm srm turbos, srm wastegate, srm air intake , apr dp , milltek exhaust, map 4 , flex fuel kit ( lines and sensor) , relocation turbo oil screen , DS1 tune , srm tcu tune ....the car is incredible fast for a 4600 lb sedan....she will go on the Dyno on the Dec 10th ...satin black gold dust wrap , 21x10.5 ferrada forge wheels , 295/35 Michelin pilot sport 4s .. .anyway I never had issues before I start with stage 1 apr than move to stage 2 apr( when they were available), and than I decided to go a little crazier and I went stage 3 .....when I got to stage 3 I start having cylinder 5 misfire . The team from Srm said 2 possibilities:
1. The cheapest version ...cut out the cats on the Dp and put a straight pipe . No more back pressure on the turbos , no more misfire , finger crossed ....
2. The very expensive version ....the valve springs, lots of money, labor , etc ( FYI...apr has the upgraded valve springs ( 20 or 40 pack ) and no more problems ...
me personally I hope the cat out version would work ...
Wow. That valve shim TSB could be big deal. Has it been discussed somewhere else here on the board? Bit frustrating - even 2017:s should be avoided now...?
Last edited by erik_plus8; 12-06-2020 at 10:32 PM.
Finally she went on the dyno ..
727 whp and 777 ft lb
on level 0 ( low boost)
Running straight E85 ....
Level 1( mid low boost ) 709whp 810 torque
Level 2 ( mid high boost)
Level 3 ( high boost)
on level 2 and 3 I got a misfire cylinder 5 ....
btw , I took out the cats and no more back pressure , but still under high boost that cylinder 5 misfires
maybe it is doing it because it runs too lean
I will add 94 chevron and try to run a E60 blend
last option ... if its
still misfires than i will upgrade the valve springs with the apr upgraded ones .
Thank you guys for your experiences and opinions. I updated engine software and the gas smell is gone, but I still feel slightly noticeable rough idle, which is noticeable when A/C is off or doesnt need to work too much (winter). If I turn temperature to LO and AC starts to work for full, rough idle is gone and idle is excellent smooth similar to engine turned off. Is this OK or I have to find any other problems in car? I also had 2 times CEL with P2096 code (bank 1 post-cat o2 sensor: too lean), which I hope is only dying O2 sensor (based on experiences of others here). CEL comes after long gentle ride.
12-04-2020, 03:36 AM
S8+ misfires on 5 cylinder
