Heyst

Hey everyone, youve been more than helpful with my old TT, now after searching extensively Im begging for your help with my 2005.5 Facelift A8.

under load, roughly 1000 - 2000 rpm, the car is misfiring on only the #2 cylinder. It started as #3 yesterday, changed out that coil pack with a new R8 red top one and now the misfire has migrated to cylinder 2.

I changed out my fuel filter and tightened down my intake manifold bolts in the correct pattern - they were semi tight.

All new plugs with the proper 4 prong bosch.

What would cause bank 2 lean (cyl 5-8?), but misfires on cyl 2?

bad cat?
bad o2 sensor?
bad pcv? I noticed its making an odd noise almost like a softer groan, but I can remove my oil cap easily and there is a slight change in rpm..


Address 01: Engine Labels: 077-910-560-BFM.lbl
Control Module Part Number: 4E0 910 560 J HW: 4E0 907 560
Component and/or Version: 4.2L V8/5V G 0010
Software Coding: 0007773
Work Shop Code: WSC 02313 785 00200
VCID: 285F1E2B9B06C05EFC3-807D
4 Faults Found:

16684 - Random/Multiple Cylinder Misfire Detected
P0300 - 001 - - Intermittent
16686 - Cylinder 2
P0302 - 001 - Misfire Detected - Intermittent
17538 - Fuel Trim; Bank 2 (Mult)
P1130 - 001 - System too Lean
16558 - Fuel Trim; Bank 2
P0174 - 001 - System Too Lean

Readiness: 0010 0101

TSHong

On the freeze frame, What RPM was the codes captured at? It can tell if you have a vaccum leak or MAF type issue. I would first sort out the lean because running lean can cause misfires.

Heyst

Ill research how to figure out what rpm ithat code threw at. easiest way to ddescribe is 1000-2000 rpm. that whole range.

since only bank 2 is popping up it makes me think its post MAF. Ill smoke test it the best I can in the morning (cheap cigar trick). which vacuum line should I blow the smoke into haha

is there an injector cleaner I could safely run?
thanks

target39

Bank 2 lean condition is probably due to your removal of oil cap (located in bank 2). If it was a lean condition due to a vacuum leak/unmetered air pre-throttle body, the lean condition would occur on both banks. The oil cap and dipstick must be fully seated and sealed when the engine runs, or unmetered air can enter the combustion chamber. PCV also needs a closed system to work properly.

As for the misfire in cylinder #2, there are a multitude of factors that can cause single cylinder misfires: spark plug, ignition coil, wiring harness/connector, fuel injector, bent valves, bad piston rings/blow-back, etc.

I know you said you changed out plugs to all new Bosch 4 prong and replaced the cylinder #3 coil with a new one - which migrated the misfire to cylinder #2. Due to this, I'm inclined to think this is a wiring harness problem. Perhaps the disconnecting and reconnecting of the harness to the ignition coils caused this with a sub-optimal connection. These cars are very sensitive to resistance, so make sure you're getting proper voltage at the terminals and that the plugs and coils have good connections.

Bad sensors would throw a code.

Heyst

The code was there before I opened the oil cap. It's been popping up for a couple months now.

TSHong

If you saved your codes in VCDS, it is displayed right underneath the actual code under freeze frame and one category will be RPM.

Shamoye Lewis

this is gonna sound stupid but put 89 gas in your car for the next 3 refills.... and watch that code vanish.....

I use to always have it and I only use 93 and a day I was like really low on gas and the station only has 87 and 89 I put 20 bucks 89 went on my way next morning I start I notice car didnt misfire... so I didn't really pay attention, burned out that gas same day went back to 93 next morning misfire was back, I was like hmmmm wait a minute after 93 finished I tried back 89 no mis fire.... and I didnt get gas from the same station so its not the station, but anyways I used 89 for 4 refills and misfire was gone for ever this was almost a year ago, I now mix between two grades never misfired again....

although this might not help you its a free try.....

Heyst

Ive been using Shell 91. I was under the impression that here in Canada, at least in Alberta, it's the only petrol not mixed with E-85. I'll try 89 next tank.
Bad gas has been a suspicion.

Thank you everyone. I'm heading to Cuba today for a week still I'll post vcds update and run the new gas when I get back.

Heyst

A little update as I am still hunting this issue down...

got rid of the misfire codes for now with new coil packs and running 94 octane for two tanks.

Still suffering codes p0171 and p0174 lean bank 1 & 2 which is causing a vibration. Took apart my pcv and it was full of sludge - tore diaphragm so I replaced with new pcv.

I'm in the process of smoke testing my vacuum lines today. there is a leak coming from the front driver side around the cam area..I'm going to remove the plastic belt cover and try to get a better view of where it's leaking. ..stay tuned

Heyst

OK, so..
both IM change over pod arms are broken...typical! pods are always in deflated position. with the engine off, if I manually pull a bladder out and push it in (inflate / deflate) I can hear air gushing out of the top of the intake manifold change over valve. is this supposed to happen? could both broken arms cause my lean condition on both banks? that would be too easy right lol

Also, while smoke testing the engine, I hear a tiny leak coming from an n205 /n208 valve. no oil, just tiny tiny bit of smoke coming from that area...could this be a source of my lean condition?

one other possibility I read on here somewhere was a certain valve between the intake and brake booster. it's basically an almost v shaped check valve. I'll try to find a part number. if this is faulty I suppose this could be the culprit.

and input is much appreciated. thanks