B7 2.0T P0303 Misfire, Already replaced Coils, Plugs & F. Injectors! Code remains!!

[danteshors]

Hi all so I am at my wits end here. I thank you in advance for listing and lending any advice. 2008 B7 A4 2.0T 6M 94K miles

One day I go out to start the car and it sounds terrible like it is missing on a cylinder. I run the car home and pull the codes and see the P0303 Cylinder 3 misfire. I swapped coil and plug from #2 to #3 and the code came back STILL on #3 but I swapped out the coil anyways on #3. The car felt better however the problem came back with what feels like a failure to spool on the high end and a bad stumble at idle speed. Also when I get up to higher RPMs I can tell the car is not producing the power and it frequently goes into limp mode with the CEL constant on. So since I replaced the plugs and coil my next thought was a clogged injector. I then began a concerted effort to clear out that injector using fuel injector cleaners. I ran a couple tanks of gas and 3 or 4 bottle of fuel injector including 30 oz of Techron through the system. No changes so I went ahead and bought all 4 new fuel injectors and pulled the intake manifold off and swapped out all the injectors and changed out the fuel filter with the Mann one. Reset all the codes and the same issue exists. What else could it be? There are no other codes except #3 misfire. I use my bluetooth OBD2 and my phone to reset the codes to get out of limp mode when I drive but this can't go on forever. When I looked at the valves they looked a little caked up but not clogged by any means.

What's next here for me to try? Thanks for any help here!

[danteshors]

Is there any additional data that I might grab to evaluate what specifically is causing the P0303? I'm using a bluetooth dongle using Torque Light and I just keep retrieving the DTC codes and resetting it to get the MIL off but there has to be a more elegant solution.

[kt883]

maybe try a compression test/leakdown test to determine health of cylinders/pistons if you've tried coils sparks and injectors. Also check the harness for broken wires as that could also cause misfire and is likely culprit if compression test is good.

[jpepsi]

I've had a similar issue. Car was terribly shaking due to misfiring. The scanner pulled code P0303 Cylinder #3 Misfire. I've had new coilpacks and new spark plugs. We've came to the conclusion that the injector on Cyl. 3 was faulty. I bought a brand new Bosch injector and we've plugged it in. When we start the car it was still misfiring, there was absolutely no change at all after installing the new injector. My mechanic checked in the valves while I was cranking and he notice no fuel was coming out of the new injector as well. He came to the conclusion that we'll probably had to look at the wiring or to have PCM (ECU) replaced since this one is probably sending a bad signal to injector #3. So I went back home with the misfires and the car was horribly shaking so I didn't use it for 24h. When I got back to the car the next day it was still shaking on cold start, there was no change, then as soon as I backed it up of my driveway I felt like the misfires was gone. I've hit the highway and the car was back to its normal state. So it seems like it takes some time to have a new injector working properly. I'm still testing the car and will let you know if there's any new fault or something similar.

[danteshors]

So quick update:
I bit the bullet and took it to the dealer to a mechanic I trust. He suggested an intake cleaning since everything else I had done already. This included pulling the intake manifold off and do a camera inspection of the valves then fill the tops of the valves up with decarbonizing juice, scrape and suck it out after an hour. Do that 3X. So I got the call earlier today that the procedure was done and the car is STILL having P0303 misfires at 4K RPM under a load. The idle smoothed out but it did not fix the top end issue. Next step he said was to rebuild the head at a cost of $3500. I asked about compression and he said all the cylinders were fine. He believes that the valve guide is worn due to excessive carbon build up on the valves which cause the guides to wear oblong grooves in them and at high rpm the valves wiggle and do not seal properly.

Anyone else see this too? He said that I was not the first person that this has happened with with a B7 direct injection 2.0

[danteshors]

I am headed to pick the car up today. Anyone have any thoughts here on my next steps? Pull the head and have it re manufactured and cleaned out?

[danteshors]

Anyone have any leads in the southeast that will do some quality head work?