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Discussion Starter · #1 ·
Hi,
my S5 (2008 CAUA engine) with 212k km / 132k mi started misfiring on cylinders 1-4 (whole right bank) every time when I hit 4,3 - 4,5k RPM. During this, the Check Engine light starts flashing and turns off as soon as I put the engine under load at low RPMs.

VCDS's freeze frames suggest that cylinders do not misfire all at the same time but rather each cylinder during different occasions (e.g., cyl 1 on Monday morning, cyl 3 on Monday evening, cyl 2 on Wednesday, and so on.) Unfortunately, I can't post the VCDS log since it's in russian.

Does anybody know what could be the cause of it? My best guesses are:
  • flaps in the variable intake manifold giving up,
  • heavy carbon buildup (probably never been cleaned),
  • dirty/contaminated injectors, or the whole fuel system (especially HPFP).
I suspect that the engine changes its air and fuel operation at 4,3 - 4-5k RPM and some of the involved actors are not adjusting their operation correctly.
 
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Sounds very similar to when my HPFP went on my B8 S5. At high revs I'd feel a loss of power and the EPC light would come on. Believe there was not enough fuel being pumped in so replaced that pump (and cam runner - may as well whilst you're there) and it worked fine after that
 

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Discussion Starter · #3 ·
Sounds very similar to when my HPFP went on my B8 S5. At high revs I'd feel a loss of power and the EPC light would come on. Believe there was not enough fuel being pumped in so replaced that pump (and cam runner - may as well whilst you're there) and it worked fine after that
Oh yeah! That's right! When I tried to "push through" the missfire the EPC light came on too. Unfortunately, I don't remember if the VCDS cought any other DTC. Now I've gotten into engine maintenance and took off the intake manifold so I have no option to test the issue again.

I'm planning to decarb, clean and calibrate the injectors, replace spark plugs, clean and check the variable manifold flaps, and replace the oil filter housing gasket. I'll try to diagnose the fuel pumps while I'm at it to see if they're still usable.
 
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Ray tell us your progress, your plan sound good.
 

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Discussion Starter · #5 ·
I'd like to update the situation. By some (un)fortunate coinsurance I've found out that my cats are loose in their housing and badly crumbling - I'm shooting parts of them through my exhaust.

So I've added a catless downpipes along with stage 2 remap to my plan of repair/maintenance.
 

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Discussion Starter · #7 ·
MC-10138345-9999.pdf (nhtsa.gov)

Take a look here. Have your cats replaced under the recall if you can. Even if you want to go catless, you can still get some brand new cats to hang onto for the future.
Thanks for the tip. I'll try to confirm if the recall is valid for EU cars too. Spare cats would certainly come in handy since OEM ones cost approx. 2k EUR each.
 
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