Misfire and smoke

Working on a 2013 Audi s6. 4.0 twin turbo v8. 

car shakes from cylinder misfire. Also has p0305 for cylinder 5 misfire. I swapped coil and plug with cylinder 7 and 5 and no difference. When unplugging coil connector on 5-8 the engine makes a difference. But when pulling coil harness for cylinder 4 there is no difference, makes me think the computer is wrong and it’s actually cylinder 4 that is a dead hole. Along with it, the car has a good amount of white smoke coming from exhaust. Open to all the help I can get. Thanks 

Does the white smoke smell like raw fuel? What are your trim numbers and what does the fuel rail psi do on shut down? It should hold and if the engine is hot, it should increase

Fuel rail pressure did increase while engine was hot and not running, left and right side differed by 50psi… not sure if that means anything. Smoke gets worse as vehicle heats up.
Bank 1 short term and long term was at 0.00.
Bank 2 short term is -7.7
Bank 2 long term is 0.00.
smoke smells like oil, no fuel smell at all. Thinking of performing compression check on cylinder 4…? 

This is GDI engine if that makes a difference. Injectors are a huge pain to get to so if there are anyways of testing those without touching them that would be awesome. Thanks for the help

I would pull off the intercooler hose and check for oil in hose. If oil there disconnect the inducer connection at turbo housing and wiggle inducer blades with your hands. If it wiggles or has back and forth play the bearing in turbo is shot. Which will spray oil into exhaust and intake causing your condition.

If it checks out ok smell oil to see if it smells like gas. Sometimes the gdi hi pressure pump seals will fail causing the oil in the pump to mix with fuel and spray into cylinders making a similar smoke (but not always).

A compression test would be the next step if all above are ok and then lastly checking intake valves for oil and carbon buildup from leaking valve stem oil seals.

My hunch is the turbo bearings went if that is the case you will need to replace the oil feed line along with flushing engine of oil coking deposits and lastly turbo assembly with gaskets.

Also check your cats as they will need cleaned out or replaced and exhaust manifold cleaned out.

Little back ground info, we just put two new turbos on the car, have not driven it at all since. Still on the rack from install. As soon as I started it the CEL started blinking and that’s when I got the EPC light and smoke as well. After the compression check showing good I’m not sure where to go from here. Any help is appreciated. Thanks

Did the old turbos leak oil ? Odds are if they did it would have fed quite a bit into the exhaust so you will be burning the remainder in the exhaust.

Hard for me to say as the car was towed to us already taken apart from a different shop.

How soon on start up does the exhaust emit white smoke? Have you checked injector waveforms for a stuck open injector or or used a stethoscope to hear it click?

It seems to take a few mins or more to start smoking, I’m thinking as it gets hotter it smokes more. I have not checked waveforms as I do not own a scope yet. I could try the stethoscope idea though

Ok I think when the cats get warm enough they start burning the oil off of the substrate in the cat I would say pull the o2s and video scope upstream for black sludge aka burned oil in the exhaust pipes and cat. Odds are the owner didn't want to put new cats and exhaust on. Or was not advised on it.

A little more info on this. Car does not have cats on it. We performed an additional compression check last night per Audi standards, engine warm, plugs removed. Cylinder 4 was 30psi different but still 180 psi, all other cylinders were around 210psi. What was strange though is after we put the plugs and could back on, the vehicle struggle to start because it seemed to have flooded it from injectors running while performing compression check, but when I put the accelerator pedal to the floor to clear it, it fired up and revved up a bit, maybe 3000-3500 rpm which was expected, but after that the car idled great and no misfire counters were active and you couldn’t feel a misfire at all. Then after about 45 seconds at idle the car started to misfire again and this time for cylinders 3,4,5. I almost wonder if the injectors are flooding the cylinder/cylinders and when it revved up it cleared it out for a bit. Let me know your thoughts and thanks for the help.

Also, could a vacuum leak possibly be causing these symptoms? I feel I would get a fault code for something like that but maybe not.

Hey guys,
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So is definitely not related to fuel trim?

I mean you confirmed those 45 seconds the smoke shows up doesn't match with closed loop starting?

Well, to whom it may concern, I finally figured it out. After trying everything under the sun in my diagnostic skills and nothing really adding up to make sense accept possible faulty GDI injectors stuck open. Unfortunately you have to drop the engine out of the car to replace them. Well engine was dropped and started to proceed with replacing injectors and then I found rags stuck in the intake manifold runners of cylinders 4&5. The shop that previously had it put rags in the intake to stop debris(my hypothesis) and never took them out. It was then towed to our shop. I don’t use rags just for accountability sake. Thought I would share the crazy ride this has been. Thanks for any and all help

Wow, glad you found it!