# 2007 A6 4.2 Misfiring under load



## BklynRX7 (Feb 22, 2010)

Hey guys, Ive searched this topic and received the same 2 possible answers that I got from 2 different mechanics. Im just hoping that I can get some clarification here. My A6 has 110k on the odometer and recently started misfiring under load. I can rev high and do any speed I want as long as its gradual. If I punch it, it misfired around 3k and the car stumbles and drives rough for a bit. One time during a really cold storm it misfired on startup, but it hasn't happened since, even in worse conditions. I pulled the codes and the misfires were happening on multiple cylinders.

The first mechanic I spoke to says that its the known carbon build up issue and i should get that taken care of, this will run about $1400. He ruled out the plugs and coil packs because, its happening on multiple cylinders. The second mechanic deals with RS4's and has one of his own. He states he has never had to manually clean carbon from valves and the misfires are probably from coil packs, which will run about $600 with plugs and labor, or an evap problem. He looked at the car this week and said the coils were ok. They "smoked" the motor and found a leak on the manifold that they tightened up. They also pulled these codes for the following errors:
multiple cylinder misfired
misfire on cylinders 1, 3, and 5
all occurring at around 30% load
There was also a code for errors with the manifold flapper, that I don't have infront of me.
I drove the car after he tightened the manifold and is still running really rough.
Im going to swap the coils and plugs and see if that helps. I was just wondering if you guys had any idea what I should check out.


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## g2turbo7 (Nov 5, 2004)

The coil packs may be going bad, but it's unlikely to be the root cause-- at this point. Multiple mis-fire DTC's usually mean there's a fuel delivery issues or massive air intake leak. 

Is the fuel filter old? Does the fuel pump sound bad? Is fuel pressure correct, including under full WOT load? 

The cam sensors could also be going bad, but usually will first set a code.... 

Carbon buildup isn't the root issue...but should only use Top Tier gas, and I like Amsoil PI fuel treatment-- works great and use it on our customer cars and the shop RS6.


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## 9aba16vt (Feb 28, 2011)

Cyl 1 3 and 5 are on the same side.... so it sounds like an intake leak.. thats the only thing that has all cyls on one bank in common


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