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Author Topic: c5 rs6 high negative (partial) fuel trims  (Read 7695 times)
airtite
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« on: July 14, 2021, 11:30:04 PM »

Hi

I had a stage 2 tune done for my car last year and the car was going into limp with a boost limit exceeded fault, I changed the n75 which seemed to have stabilized the issue but under hard acceleration in 4th it would go into limp still, I reverted the flash back to stock and have been driving the car that way since.... since its not really a daily I havent really worried about it much.

Anyway decided to do some work on the car and fixed a slight oil leak it had and did some other maintenance and ran a vcds scan with the scan coming back with intermittent rich conditions on both banks and block 32 002/004 showing -14% on both so the car is obviously pulling fuel. I cant see/hear any obvious boost leaks and I did replace all the boost pressure hoses with silicone replacements last year.

Any thoughts on what to start looking at?

Logs from last year attached stock file and stage 2 (cant do any logging currently due to the chaos/riots going on here in SA currently)
 
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nyet
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« Reply #1 on: July 15, 2021, 12:05:58 AM »

log o2 voltages and ps_w

if you have access to a wideband try that.

but your wgdc is 95% up top which also points to a boost leak

pressure test.
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airtite
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« Reply #2 on: July 15, 2021, 03:28:41 AM »

will do a pressure test as soon as I can get out and get the stuff to build a new pressure tester
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airtite
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« Reply #3 on: July 19, 2021, 07:04:34 AM »

did pressure test, looks like leaky passenger side intercooler (rhd car)... going to see if I can get them recored.
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airtite
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« Reply #4 on: July 24, 2021, 02:24:43 AM »

ok so intercoolers repaired, everything assembled took the car for a drive, car is driving really strong but now I have a -9.4% partial on bank 1??? bank 2 is 0% where too from here?
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nyet
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« Reply #5 on: July 24, 2021, 01:37:32 PM »

injector issues or you still have a leak somewhere
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prj
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« Reply #6 on: July 24, 2021, 01:43:18 PM »

Probably no pressure test was done.
Disconnect IC hoses, plug one, put 1 bar in the other.

Or waste your time chasing tails, your pick.
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terok
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« Reply #7 on: July 25, 2021, 03:29:18 AM »

Yeah, likely the other one is leaking also. They often crack inside of the end tank seams, where you cannot really see it.
Of course a lot of other possibilities in these multi-problem vehicles.
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airtite
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« Reply #8 on: July 25, 2021, 11:23:14 PM »

Yeah, likely the other one is leaking also. They often crack inside of the end tank seams, where you cannot really see it.
Of course a lot of other possibilities in these multi-problem vehicles.

Both intercoolers were done and pressure tested, what doesnt make any sense to me is if it was a boost leak I should be seeing high negative fuel trims on both banks not just one because the boost system is connected ie both turbos connect to a single point.
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prj
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« Reply #9 on: July 26, 2021, 03:46:17 AM »

Probably lambda regulation is not even working on other side.
You pressure tested intercoolers off the car, not the entire intake system right?

So essentially you didn't test anything.

Why is this thread even continuing?
If you can't do a pressure test on the car, which literally takes 20 minutes on a lift, then maybe just stop doing this lol, it's pathetic.
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airtite
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« Reply #10 on: July 29, 2021, 04:32:40 AM »

Probably lambda regulation is not even working on other side.
You pressure tested intercoolers off the car, not the entire intake system right?

So essentially you didn't test anything.

Why is this thread even continuing?
If you can't do a pressure test on the car, which literally takes 20 minutes on a lift, then maybe just stop doing this lol, it's pathetic.

Hi PRJ, intercoolers were pressure tested off the car by the radiator/intercooler repair place and I pressure tested the entire intake system once they were reinstalled.
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Philrs2
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« Reply #11 on: January 31, 2022, 09:22:20 PM »

I just HAD to register after reading this thread.
@ prj, slightly harsh comments? Cheesy
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airtite
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« Reply #12 on: February 03, 2022, 10:50:48 PM »

as a follow up, i started having a oil smoke on deceleration issue which I initially thought was a leaky check valve but after pulling the intake manifold and doing some other stuff I found oil in the right hand side downpipe which ended up being the turbo. I had both turbos rebuilt and car is back up and running normally.
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prj
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« Reply #13 on: February 04, 2022, 01:44:45 AM »

These cars don't make any boost at all if one turbo is blown, as air just recirculates through it.
I'd guess there was some issues with turbo inlet/outlet. Also the seating of air intake on this car is a nightmare.
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airtite
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« Reply #14 on: February 05, 2022, 02:10:30 AM »

These cars don't make any boost at all if one turbo is blown, as air just recirculates through it.
I'd guess there was some issues with turbo inlet/outlet. Also the seating of air intake on this car is a nightmare.

It was boosting but leaking oil and the turbine/compressor wheels had both had damage from shaft play.
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