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Hello all, I used to be a member here almost 23 years ago when I had my 2000 S4. I've since forgotten my old account, so I had to create a new one. I am hoping to get some assistance with troubleshooting my issue with my 2008 S8. I was driving to work when the check engine light came on. When I pulled into a parking spot, I noticed that the idle was rough. Started it up at the end of the day and it was still idling rough. Drove home without issue and only noticed the roughness at stops along the way. Ran VCDS and I remember it showing faults on/in 'Lean Fuel Bank 2' and 'DTC Memory of ECU Number 2'. It did not state there were any miss-fires at this time.
I read through all the posts I could find on here for these 2 faults and found posts about changing the 'High Pressure Fuel Controller'. I was able to get 2 of them in a day and swapped them out. Sadly, I cleared my codes after to see if that fixed the issue. It didn't! I even think that it made it worse. I put the OEM Fuel Controllers back in so I don't chase additional problems later. I then ran the engine for a short period of time until the check engine light started flashing. Needless to say, it was running really rough at idle and when I would try to rev the engine, it would sputter before climbing in RPM's; however, it wouldn't stay up there, after about a second, it would drop back down, on it's own, to a rough idle.
I then checked the barometer and the fuel pressure live in VCDS while revving the engine in the garage and never saw a difference between the two (the 2 barometer readings and the 2 different Fuel Pumps). Both were pretty much identical the entire time. This test was also recommended in various posts on here.
I believe that the next troubleshooting step should be to unplug the MAF's and see if it runs properly; given that the computers should reset back to a default fuel ratio. Does anybody have any instructions on how/where to unplug the MAF's on a 5.2L engine? I believe that this will tell me whether it's a MAF or O2 sensor issue. I've felt around the intakes trying to find a hole/gap/break, but I think I would need the smoking thing for this test. Anybody got a smoke tester in the N. Dallas area?
Or is there something else that I should check?
I copied the latest VCDS after I put the original Fuel Controllers back on and pasted the output below. From reading this, it tells me to replace Coil Packs. I don't believe that this is the correct solution to my problem given that this wasn't in the original VCDS output. I think this is a byproduct of my original issue. I'm worried about driving the car with this many miss-fires because all that unburnt fuel will destroy my cats.
I'm really hoping that this forums experience can assist me with this conundrum. I'm at your mercy. Ideas?
Address 01: Engine Labels: 07L-910-552-BSM1.clb
Control Module Part Number: 4E0 910 552 K HW: 4E0 907 552 A
Component and/or Version: 5.2L V10/4V FSI ª0040
Software Coding: 01060009190F0260
Work Shop Code: WSC 26153 444 103839
VCID: 2A0D108530FA95FA517-807E
1 Fault Found:
006435 - Please Check DTC Memory of ECU Number 2
P1923 - 008 -
Freeze Frame:
Fault Status: 01101000
Fault Priority: 2
Fault Frequency: 1
Reset counter: 255
Mileage: 255635 km
Time Indication: 0
Date: 2024.04.19
Time: 12:20:38
Besides vacuum leaks, consider the low pressure fuel pump(s)--the ones in the tank. Notice your misfires are all over the engine, so it isn't just one side, or even one bank of one side. (For V10'S and W12's there are four banks for O2 sensors or cat issues.
When was last tune up relative to current miles?
For MAF's, honestly just look for them under hood--one on each side after the air boxes. On a W12 they are in the center of the air box on exit side. You squeeze the upper part of connector lock tab inward then push down slightly to release locking tab, then pull up. Must be videos on it. My old 2000 A6 4.2 unlocked the same basic way. NEVER pry with a screwdriver.
For low cost and good maintenance anyway, give it a couple of Techron treatments when filling. Won'r do squat for intake valve type stuff, but can help clean up fuel system internals and injectors.
Coil packs are a low probability too, but never say never. Coming on suddenly and across so many cylinders doesn't add up though. From W12 experience, even with a prior recall on them, they were junk as of early this year on a 2006 W12 at 175K miles (probably 140K on the recall replace set). No codes either, but clearly arcing to the valve covers. W12 is metal, while S8 is plastic IIRC so not same ground path.
Last edited by MP4.2+6.0; Apr 27, 2024 at 06:03 AM.
It’s a common misconception that the HPFP’s are bank specific because there happens to be one mounted on each bank. They’re not, and they both feed the same common fuel rail that feeds all 8 (or 10) injectors.
Not realizing this can lead to you going some pretty big diagnostic dead ends.
Have only had this for a year, so I don’t know when it had a tune-up last. I have put a few tanks with Techron through it, but the last time was a few months ago. Any suggestions on how to do the smoke test? Can I use a smoke gun for smoking meats to test it? Or do I have to use one for cars?
I found the leak! Would somebody be able to tell me what goes in this hole on the front of the intake manifold? I don’t see anything loose or hanging that’s not plugged in already. Can you provide a pic of what goes there?
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Rough Idle and Low Fuel Pressure Issue
