Misfiring (Cyl 4) P0304 Air/Fuel Imbalance (P21900F)

[WeldLife88]

Good morning all!
I will make this as short and sweet as possible..

Car: 2015 S3 (DSG) 60k, APR Stage 1


Last Monday I noticed some staining under the car on the street... Took a look and the water/thermo housing was leaking. It was mighty cold where I live so I opted to bring it to a VW dealer and let them do the work. While they were there I requested a De-carb be done.. The next day and $2100 later the car was done.. Great... Driving the car home, it felt great, throttle response, fuel economy was up. Fast forward to last night, I was driving home on the onramp to the highway, I decided to have a little fun so I stepped on the gas ( not WOT) just enough to put a smile on your face. The car got to about 4k rpm and It felt like the fuel or such a was cut off or something, I backed off the accelerator for a few moments, I thought it could be me possibly confusing the DSG.. Did it again and the same event happened.. no CEL no lights of any sort.. I finally got home, parked car and let it idle.The idle was irregular ( jumping rpms, car running rough) Plugged in OBD11 and got a misfire Cyl 4 (P0304) and Cyl 4 Air- Fuel Ratio imbalance( P21900F). I did swap coils/ plugs to see if it followed (misfire remained on Cyl 4) I had the car towed back to VW.. I'm thinking maybe fuel injectors? Is this just a coincidence or maybe a result of an improper decarb? valve not sealed and carbon and crap entering the combustion chamber fouling the injector? I'm hoping this is not a ring or valve problem as I've read some horror stories regarding similar instances.( With these symptoms and codes)


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[evo v]

In order to remove the intake manifold on this gen you need to disconnect the fuel rail. When you pull the manifold out sometimes the injectors come out with the manifold. It could be that when they install them back the injectors were not properly seated or connected.

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[MikTip]

In order to remove the intake manifold on this gen you need to disconnect the fuel rail. When you pull the manifold out sometimes the injectors come out with the manifold. It could be that when they install them back the injectors were not properly seated or connected.

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The S3 motor...E888.3 uses direct injection fuel injectors. 4 of them.

These injectors have a "seal" near the spray end which "seals" it inside the combustion chamber.

If the injectors were removed...this seal has to be replaced. Or the combustion chamber gasses leak out past the injector.

[MikTip]

Good morning all!
I will make this as short and sweet as possible..

Car: 2015 S3 (DSG) 60k, APR Stage 1


Last Monday I noticed some staining under the car on the street... Took a look and the water/thermo housing was leaking. It was mighty cold where I live so I opted to bring it to a VW dealer and let them do the work. While they were there I requested a De-carb be done.. The next day and $2100 later the car was done.. Great... Driving the car home, it felt great, throttle response, fuel economy was up. Fast forward to last night, I was driving home on the onramp to the highway, I decided to have a little fun so I stepped on the gas ( not WOT) just enough to put a smile on your face. The car got to about 4k rpm and It felt like the fuel or such a was cut off or something, I backed off the accelerator for a few moments, I thought it could be me possibly confusing the DSG.. Did it again and the same event happened.. no CEL no lights of any sort.. I finally got home, parked car and let it idle.The idle was irregular ( jumping rpms, car running rough) Plugged in OBD11 and got a misfire Cyl 4 (P0304) and Cyl 4 Air- Fuel Ratio imbalance( P21900F). I did swap coils/ plugs to see if it followed (misfire remained on Cyl 4) I had the car towed back to VW.. I'm thinking maybe fuel injectors? Is this just a coincidence or maybe a result of an improper decarb? valve not sealed and carbon and crap entering the combustion chamber fouling the injector? I'm hoping this is not a ring or valve problem as I've read some horror stories regarding similar instances.( With these symptoms and codes)


Sent from my Pixel 7 using Audizine Forum mobile app

Cyl 4 Air- Fuel Ratio imbalance( P21900F)

Looks like a bad injector.

[MikTip]

I replaced all 4 of my injectors on my 2015 S3.

The oroginal 2015 injectors on the car installed at the factory were "L" version.

The new replacements were "AK".

The injectors have been updated allot by VW/Audi...

[WeldLife88]

Yes I did read your post on another members issue.. it's honestly what made me think and hope it's only faulty injectors and not something more..

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[WeldLife88]

Regarding the removal of the Fuel rail/ Injectors.. is this something that's normally done when replacing water pump assembly and a carbon cleaning? Or a preventative measure?

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[evo v]

It's easier to get to the thermostat and the pump with the intake manifold off. I've replaced them without removing the manifold but you really need to know where the bolts are. You have very little space to work with. The most difficult part is installing properly the little plastic union between the thermostat and the oil cooler. If not done right you will have a slow coolant leak.

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[MikTip]

Regarding the removal of the Fuel rail/ Injectors.. is this something that's normally done when replacing water pump assembly and a carbon cleaning? Or a preventative measure?

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Depends on the shop and mechanic and how many hours labor they charge for the job. Removing the injectors makes it easier to do the thermostat housing. The water pump sits on the drivers side of the thermostat housing and by the factory manual can be replaced without removing the intake or injectors.

[WeldLife88]

VW called.. Diagnosis: Cylinder 2 and Cylinder 4 Fuel injectors shit the bed.. Replacing all 4 with the revised AK injectors.. Big thanks to those who helped me out!

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[MikTip]

VW called.. Diagnosis: Cylinder 2 and Cylinder 4 Fuel injectors shit the bed.. Replacing all 4 with the revised AK injectors.. Big thanks to those who helped me out!

Glad to hear it was properly diagnosed!

Too many people dont realize there is a fueling issue and keep pushing boost...thinking somehow it will fix itself and unfortunately destroy a motor....