1st Gear Power Cut

5.0 V10 50v biturbo - 571 bhp
cammmy
2nd Gear
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1st Gear Power Cut

Post by cammmy » Wed May 04, 2022 3:14 pm

Hi All

I have an MRC stage two car that recently started often hitting some kind of rev limit in 1st at around 5k rpm (full throttle). Power cuts and it makes the "DSG Fart" noise (I know it's not DSG).

I've tried turning TC off fully but it still happens. Also doesn't feel like it's spinning wheels.

The only thing I can think of that's related is that I found and fixed a boost leak a little while ago. If it was an overboost issue though, I would expect it to be more of a problem as the gears go up?

I'm going to get the laptop on it but just wondering if anyone has had something similar and can point me in the right direction?

Ta
Cam

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IanH755
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Re: 1st Gear Power Cut

Post by IanH755 » Wed May 04, 2022 5:14 pm

Something else to check, at the same time as checking the boost levels, is for fuel pressure as the ECU will cut power via fuel cut if it sees the fuel pressure drop below a "certain figure" (IIRC 3bar but I'm not 100% sure on that figure TBH, could be a bit lower). The fuel pressure should be constantly at (or extremely close to) 5bar even under boost with a healthy LP tank pump, 2x HP pumps and good filter.
***OLD*** Daytona C5 RS6 Avant - MRC'd - 500HP & 820NM (PistonHeads Link).

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cammmy
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Re: 1st Gear Power Cut

Post by cammmy » Wed May 04, 2022 9:41 pm

Very good point, thanks for that. The fuel filter is probably the only thing I haven't done on it. Slightly embarrassed I didn't think of it :lol:

I'll order one up and get the laptop on it after that.

cammmy
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Re: 1st Gear Power Cut

Post by cammmy » Sat May 07, 2022 3:10 pm

Got the filter changed, what an absolutely hateful process. I have fuel line pliers but they were absolutely no use.

Looks like the fuel filter was the original one, date code of '08. That's pretty good given how much fuel it must have filtered to move this thing 93k miles. It's currently parked behind something else, will report back next time I drive it.

Pajo
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Re: 1st Gear Power Cut

Post by Pajo » Thu Sep 01, 2022 9:05 pm

Hi Cammmy
Did the fuel filter solve your problem?
Cheers.

cammmy
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Re: 1st Gear Power Cut

Post by cammmy » Fri Sep 02, 2022 10:34 am

I think so but I've had it happen once since then. I scanned it and it showed a lean condition on one bank but the snapshot said it was at about 1,400rpm, so I'm not sure it's related. When it happens it's at around 4,500-5,000.

I've cleared codes and will re-scan in the future.

Can VCDS record graphs for boost/fuel pressure?

Pajo
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Re: 1st Gear Power Cut

Post by Pajo » Fri Sep 02, 2022 8:33 pm

Okay, it happens around 4000-4500rpm on mine too. I've read at some other forum with a guy that had same issue and it happened to be one of the turbulence flaps that had shifted out of alignement, they are located under the intake manifold. It's partially common issue on these engines.

cammmy
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Re: 1st Gear Power Cut

Post by cammmy » Fri Sep 09, 2022 1:00 pm

Hmmm, I hope not. Would that show up in other gears? What I don't understand is why it's only in 1st. I would expect the higher gears to show the issue as there's more load for longer.

Pajo
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Re: 1st Gear Power Cut

Post by Pajo » Sat Sep 17, 2022 6:56 pm

Well, I would say the mindset would be same when you changed the fuel filter? But actually I have also found a vacuum leak on mine, the plastic tube/hose for the diverter valve has a split in it + the diverter valve doesnt work on one side. So perhaps this is my issue.
Regarding power cut in 1st gear I would imagine the boost builds up and peaks fast in 1st gear, so that could possible be why it cuts power in that gear only. But im not sure.

ATinOf
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Re: 1st Gear Power Cut

Post by ATinOf » Sun Oct 16, 2022 7:43 pm

VCDS can graph but I believe you have to do it live rather than record and take snapshots, but I could be wrong its been a while since Ive had to do it

Pajo
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Re: 1st Gear Power Cut

Post by Pajo » Wed Nov 23, 2022 11:51 am

Have you checked you air filters? I have just recently swapped mine out for a set BMC's and the cut in 1st gear is gone and it pulls very nice all the way up. I didnt notice the old (Stock) filters being that dirty, but maybe they were.

cammmy
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Re: 1st Gear Power Cut

Post by cammmy » Wed Nov 23, 2022 11:54 am

I've got a set of those in there. They probably have about 4k miles on them. Will pull them and wash.

Cheers

cammmy
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Re: 1st Gear Power Cut

Post by cammmy » Wed May 24, 2023 9:33 pm

Okay, the car has been off the road for 6 months but it's all MOT'd again. Unfortunately I still have this issue but now I have logs, below are the relevant bits:

000568 - Manifold Pressure / Boost Sensor (G31)
P0238 - 001 - Signal too High - Intermittent
Freeze Frame:
Fault Status: 00100001
Fault Priority: 2
Fault Frequency: 1
Reset counter: 255
Mileage: 153170 km
Time Indication: 0
Date: 2023.05.21
Time: 14:52:11

Freeze Frame:
RPM: 0 /min
Load: 0.0 %
Speed: 0.0 km/h
Temperature: 16.0°C
Temperature: 19.0°C
Absolute Pres.: 1010.0 mbar
Voltage: 12.192 V

000578 - Manifold Pressure / Boost Sensor 2 (G447)
P0242 - 001 - Signal too High - Intermittent
Freeze Frame:
Fault Status: 00100001
Fault Priority: 2
Fault Frequency: 1
Reset counter: 255
Mileage: 153170 km
Time Indication: 0
Date: 2023.05.21
Time: 14:52:11

Freeze Frame:
RPM: 0 /min
Load: 0.0 %
Speed: 0.0 km/h
Temperature: 16.0°C
Temperature: 19.0°C
Absolute Pres.: 1010.0 mbar
Voltage: 12.319 V

Had the car a few years now and this only started last summer. It's an MRC stage two with secondary cat delete, Milltek cat back and (freshly cleaned) BMC panel filters. Any ideas where to look? Also, anyone know what boost the MRC cars usually run? I'm guessing the absolute pressure listed is atmospheric? Doesn't seem to be giving me the boost pressure it saw?

Jim Haseltine
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Re: 1st Gear Power Cut

Post by Jim Haseltine » Wed May 24, 2023 11:31 pm

Used to get something similar on Ur quattros with the MB engine - hit a bit over 4000 revs in 1st with a wide open throttle and the next thing you knew was your head snapping forwards when the power cut out. If you lifted your foot a bit just before the 4000 point the car would surge through though. Generally caused by a dirty 'inlet air temperature sensor' - technically the correct term for the part but its task was to measure boost pressure. A clean up with carb cleaner spray was usually enough to sort it.
Entirely different method of fuel injection to that used on the RS6 so may not be the same cause but I wouldn't think it'd hurt to take the pressure sensors out and clean them.

cammmy
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Re: 1st Gear Power Cut

Post by cammmy » Thu May 25, 2023 8:45 am

Yeah, that's exactly what I'm seeing. If you pedal it right, you can get it through with no power cut. Will pull them and clean.

Are there just the three? One in each charge pipe and at the front of the plenum? Any reason to not ultrasonic them?

Ta

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