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Wolfgang
Wolfgang, Audi master tech
Category: Audi
Satisfied Customers: 4592
Experience:  Senior Audi Master Tech 15 yrs
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I have a 2008 Audi Q7 4.2 FSI, engine code BAR. I have been

Customer Question

I have a 2008 Audi Q7 4.2 FSI, engine code BAR. I have been dealing with an issue for sometime now involving multiple random cylinder misfire codes, as well as a Brake Booster Mechanical Failure code.
The car exhibits its symptoms usually on startup. It could be cold or warm when starting, doesn't really matter. The engine will sometimes stumble and misfire for a few minutes. Sometimes it will just crank endlessly until you press the start/stop button again to stop it, then press it again and it cranks and starts up.
When it starts, it usually smells rich, pointing to a possible leaking fuel injector, but it could also just be cranking so long that is builds up fuel in the cylinders.
The brake booster code in conjunction with the misfires really points to a vacuum leak in my opinion...I've searched before with a smoke machine to no avail. I will look again soon.
I generally have adequate knowledge of the issues with my Audis. I also have VCDS.
I really need some things to start checking as this is getting old and I can't figure it out.
Please only respond if you have detailed knowledge of this engine.
Thanks.
Submitted: 10 months ago.
Category: Audi
Expert:  Chris (aka - Moose) replied 10 months ago.

Welcome, I'm Chris (aka Moose) I prefer to work when others don't, I am here around lunch and after dinner till after midnight.

  • Sorry no one has helped yet.
  • This is not an answer to your question, just an inquiry if your still needing/wanting help. Because I believe I can help.
  • I am travelling and on vacation this week but will do my best to get to you when online.
Expert:  Wolfgang replied 10 months ago.

Thanks for choosing Just Answer . I'm Wolfgang , Master Audi Tech here to help!!

I am confident we can resolve your problem together. Please
understand that I don't know your skill level. In most cases when you have a problem
with the way the vehicle performs, specialized tooling is required to acquire computer
data/information or engine testing results. We didn’t build these complicated vehicles; we
just diagnose and fix them. Also understand that I can't see, smell, hear, or touch the
vehicle either, so it may take a few replies to get to satisfactory results.

Note there may be an issue where the complexity of the issue will require a Premium Service. This service will be an addition to the normal question cost. Usually it does not come down to this but keep in mind!!

I am also going to direct you with the fastest, easiest and most common things to check first. Please be
patient and permit me to do what I do best.
I also try to give all of the information you may need, expecting a “positive rating” in
return. I will also continue assisting you after you have rated me, if necessary. If there
is any reason I cannot get a positive rating, please let me know why “in advance”, so I
can go another direction for you. I am sorry you’re having this problem; I’ll help you
through it.
Below is my first answer or request for more information. If you do not understand it, or you need more information from me, or need me to go in more detail.

How many miles are on the vehicle ?

Any recent repairs of the vehicle before this issue ?

any recent accidents?

can you post the scan log of the engine control module and the freeze frame of the faults please?

thanks

Customer: replied 10 months ago.
Hi,
The vehicle has about 130000 miles, no recent repairs or accidents.Address 01: Engine Labels: Redir Fail!
Part No SW: 4L0 910 560 G HW: 4L0 907 560 B
Component: 4.2l V8/4V 0020
Revision: 78H02--- Serial number:
Coding: 01210009190F0D60
Shop #: WSC 31414 790 00001
VCID: 2C572A348FEC495ED1-80784 Faults Found:
005241 - Brake Boost Vacuum System
P1479 - 008 - Mechanical Failure
Freeze Frame:
Fault Status: 01101000
Fault Priority: 2
Fault Frequency: 1
Reset counter: 255
Mileage: 197664 km
Time Indication: 0
Date: 2015.08.18
Time: 18:28:08Freeze Frame:
RPM: 1980 /min
Load: 92.5 %
Speed: 18.0 km/h
Temperature: 44.0°C
Temperature: 32.0°C
Absolute Pres.: 980.0 mbar
Voltage: 13.716 V000768 - Random/Multiple Cylinder Misfire Detected
P0300 - 008 - - Intermittent - MIL ON
Freeze Frame:
Fault Status: 10101000
Fault Priority: 2
Fault Frequency: 8
Reset counter: 255
Mileage: 198105 km
Time Indication: 0
Date: 2015.09.12
Time: 20:17:32Freeze Frame:
RPM: 1961 /min
Load: 43.1 %
Speed: 13.0 km/h
Temperature: 59.0°C
Temperature: 41.0°C
Absolute Pres.: 980.0 mbar
Voltage: 13.970 V000772 - Cylinder 4
P0304 - 008 - Misfire Detected - Intermittent - MIL ON
Freeze Frame:
Fault Status: 10101000
Fault Priority: 2
Fault Frequency: 7
Reset counter: 255
Mileage: 198105 km
Time Indication: 0
Date: 2015.09.12
Time: 20:17:32Freeze Frame:
RPM: 1961 /min
Load: 43.1 %
Speed: 13.0 km/h
Temperature: 59.0°C
Temperature: 41.0°C
Absolute Pres.: 980.0 mbar
Voltage: 13.970 V000773 - Cylinder 5
P0305 - 008 - Misfire Detected - Intermittent - MIL ON
Freeze Frame:
Fault Status: 10101000
Fault Priority: 2
Fault Frequency: 5
Reset counter: 255
Mileage: 199391 km
Time Indication: 0
Date: 2015.11.10
Time: 09:56:46Freeze Frame:
RPM: 1961 /min
Load: 43.1 %
Speed: 13.0 km/h
Temperature: 59.0°C
Temperature: 41.0°C
Absolute Pres.: 980.0 mbar
Voltage: 13.970 VReadiness: 0000 0000
Customer: replied 10 months ago.
This is a scan from some time ago, but nothing mechanically has changed since then, and it has always exhibited the same issues.
Expert:  Wolfgang replied 10 months ago.

ok from the vacuum pump there is a set of plastic lines . i need you to check the lines very closely for cracks . after time the plastic line cracks at the fittings . please let me know if you find any cracks

Customer: replied 9 months ago.
Sorry for the delay, I will finish checking the vacuum lines this weekend and report back. Been busy with work.
Expert:  Wolfgang replied 9 months ago.

got it!!

Customer: replied 9 months ago.
I found a couple cracks in the vacuum line coming from the vacuum booster pump. I replaced those a about a week ago. The issue seems to have slightly improved, but is not yet completely right. Today when I started the car after sitting for a day or so, it just cranked and cranked, barely trying to start. Then, I pressed engine stop and tried again, and it started right up. It acted like it didn't have enough fuel or something. What do you think?
Expert:  Wolfgang replied 9 months ago.

you may have bleeding injectors . common with this amount of mileage!!! still also the carbon build up issue . if restricted of air how can it breath when cold . need to monitor fuel pressure run the vehicle for 2 minutes when cold then shut off then turn the key on and monitor high pressure it should go up just sitting there because of heat of the rail . monitor that for 30 minutes

Customer: replied 9 months ago.
OK, the carbon issue is not there. I had it open and cleaned it about 5k miles ago. As for the fuel pressure, you're expecting the fuel to drop off after running it for a few minutes and shutting off? If it's a leaking injector that is...
Expert:  Wolfgang replied 9 months ago.

then you need to isolate which injector is bleeding down with a borescope in the cylinder. if you see raw fuel then you have an found the bad injector. if one goes since the rest are original they will drop like flies so recommend all 8.

Expert:  Wolfgang replied 9 months ago.

anything else?

if not.....

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This rating is VERY IMPORTANT! Your rating compensates me on my time and my expertise on your issue!

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Thanks

Wolfgang