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42TT

May 10th, 2007, 13:44

Hi Guys

After doing some logs the other night I noticed that the two "Mass Air Flow" meters are reading different amount at any given RPM/Load.

I have swapped them around and the issue seems to be with Bank1. Any advice welcome. If there is any other info required please ask as I would like to get this sorted and my car 100% performance before we start modifying.

Here is a copy of the data from the logs.

Bank1 Bank2

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BORDER-BOTTOM: #ece9d8; BACKGROUND-COLOR: transparent" align=right x:num>124.11</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD style="BORDER-RIGHT: #ece9d8; BORDER-TOP: #ece9d8; BORDER-LEFT: #ece9d8; BORDER-BOTTOM: #ece9d8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" align=right height=17 x:num>110.36</TD><TD style="BORDER-RIGHT: #ece9d8; BORDER-TOP: #ece9d8; BORDER-LEFT: #ece9d8; BORDER-BOTTOM: #ece9d8; BACKGROUND-COLOR: transparent" align=right x:num>134.17</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD style="BORDER-RIGHT: #ece9d8; BORDER-TOP: #ece9d8; BORDER-LEFT: #ece9d8; BORDER-BOTTOM: #ece9d8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" align=right height=17 x:num>120.33</TD><TD style="BORDER-RIGHT: #ece9d8; BORDER-TOP: #ece9d8; BORDER-LEFT: #ece9d8; BORDER-BOTTOM: #ece9d8; BACKGROUND-COLOR: transparent" align=right x:num>143</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD style="BORDER-RIGHT: #ece9d8; BORDER-TOP: #ece9d8; BORDER-LEFT: #ece9d8; BORDER-BOTTOM: #ece9d8; 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UNit of measure is g/s.

42TT

Radiation Joe

May 10th, 2007, 14:27

Try swapping air filter elements side to side as well as checking for intake obstructions. On A/W RS6 forum there was a guy whose intake was partially blocked by, of all things, a rats nest.
You could have a bad turbo or even a partially blocked catalytic converter causing this problem as well. With about a 20% mismatch, I would expect you are pretty close to getting an engine fault code for this problem.

42TT

May 10th, 2007, 14:30

No fault codes what so ever. I have run the car with airbox removed and the same thing has happended.

I hope it isnt the turbo since the difference is evident even at idle. If it was a blocked catalytic conveter would it be safe to assume that when the car is cold this wouldnt happen as the cats are not upto operating temperature?

Thanks

Copper

May 11th, 2007, 19:18

Didn't you post that you are using K&N filters?

If you are remove them and try stock. Run again to see if that is the issue. K&N filters are pure crap.

Sean

42TT

May 11th, 2007, 19:26

yes they have been removed even tried running the car with no airbox and the problem still exists

LU-RS6

May 11th, 2007, 19:29

I have the same on mine, we measured it once just for the heck of it.
The difference tightens when I accelerate, so we guessed there is no real problem.
Difference is highest in idle.

Haven't done anything to solve this though.

skiwi

May 11th, 2007, 21:28

as you have verified that the issue doesn't follow the maf or air filter, it will be a vacuum leak.

by definition this will be worst at idle.

check the maf seals 1st. they are tricky little buggers....

the old water spray trick is still a pretty good way to test.....

skiwi

May 12th, 2007, 01:04

one thing i should have said is that you need to hold the revs constant to measure maf flow as the sampling rate on a rapidly changing rev rate is not fast enough to sample both at the same time, and so the readings will confuse.

best to hold @idle for the reasons outlined above - that is when vacuum is greatest and leaks will show up most....

42TT

May 12th, 2007, 06:01

Skiwi: Thanks I will do a datalog with the car at idle. I have noticed that the difference does vary at idle. I assume i should have the car at operating temp when I do the log?

A vaccum leak i am not looking forward to finding

Thanks

42TT

May 14th, 2007, 09:24

Okay,

I inspected the piping along the rear of Bank1. I thought i found the problem after replacing the spring clamps on a hose at the rear of the head with a pair of worm clamps when the car would idle with Bank1 and Bank2 measuring almost identical "measured air". Then i took the car for a drive and when i got back i took another data log and to my dissappointment Bank1 was again reading lower.

Not sure what it could be other then that the hose has a pin hole which is openning up under boost.

I have attached the new log and labelled the data respectively.

Thanks
42TT

42TT

May 15th, 2007, 14:35

Hi Guys

Spent most the day today spraying soapy water to try and find a vacum leak with no luck. I also replaced the hose that I thought was leaking to no avail.

I have noticed that when the car is cold the readings are very close so somehow temperature has something to do with it. Also just wanted to confirm that i am looking for a leak on Bank1 or can the leak be anywhere on the engine?

Also have the following error on the transmission computer

18265 - Load Signal: Error Message from ECU
P1857 - 003 - Mechanical Failure - Intermittent

Any ideas on other places to check for leaks or problems will be greatly appreciated

Thanks Again
42TT

Qisha

May 15th, 2007, 20:11

Dear 42TT,

does the ESP light show up?

Qisha

O.CT USA

May 15th, 2007, 20:58

42TT

May 16th, 2007, 04:01

Qisha: No the ESP light doesnt come on

OCT USA: No that was my next avenue jut have to find someone with a smoke tester

skiwi

May 16th, 2007, 07:48

interesting error - it indicates that the engine torque signal got sent by the ecm, but didn't arrive at the tcm over the powertrain canbus. there should have been a code thrown by the ecm?

if not, clear the code and see if it comes back. you could have bumped something when you were fiddling with the maf's...

42TT

May 16th, 2007, 13:32

SKIWI:

I have cleared the code and it does come back. Not sure what i could have bumped. Any areas that i should look specifically for the vacum leak as there alot of places to check.

Also does the lower "measured" air on Bank1 mean the vacum leak is on Bank1??

Thanks again
42TT

Qisha

May 16th, 2007, 13:43

Qisha: No the ESP light doesnt come on

Dear 42TT,

do you use the OE Audi ECU/TCU Firmware? Did the Car ever enter the "Limp Mode"?

Qisha

42TT

May 16th, 2007, 13:51

Qisha,

Yes the car runs standard ECU and TCU firmware. The car hasnt ever entered into "limp mode" except when the alternator was over charging and the ESP light stayed on until that problem was rectified

42TT

skiwi

May 16th, 2007, 20:17

i would leave the maf issue now, and chase the tcu code. have you logged any ecu codes (you should have)? you have elsa/bentley? that will have some diagnostic steps to follow. might be wiring or it could be an ecu fault....

FUngusmud

May 16th, 2007, 20:38

My MAF's read 10-15% off at idle also, intermittant, and 5-10% off under load. I haven't spent much time swapping them or troubleshooting yet, but will this summer. Here are a few things to keep in mind:

The MAF that is reading lower indicates it's getting outside air from someplace else, or that path is slightly more restrictive than the other MAF's path. Remember that the air path is individual from the entrance throught the filters through the turbo through the intercooler BUT then become combined at the throttle plate.

Because they are together from the throttle plate on, any "internal" engine or exhaust/cat issues will not be seen at the MAF.

You could have an AIR leak pre-turbo (because if it's post turbo, then that MAF will read low under vacumn and high under boost).

It could be an intercooler or intercooler hose is crimped or slightly blocked. It could be a turbo, but that doesn't make sense since it's occurring under no boost.

Can you please get me the output of block 32 at idle (make sure the car was driven for at least 2 hours since the last "clear codes" was issues). Block 32 will may help tell us if it's a leak or just a restriction in one side.

Maybe this is normal for our cars. Can any other RS6 users produce some block2 values at idle, part throttle and WOT?

skiwi

May 17th, 2007, 05:32

no, my values are normal (+/- 5%) at high vacuum.

just to be clear on where the leak could/should be (under idle conditions):

1) a restriction before the maf (airbox, filter restriction) will reduce flow to that maf

2) a leak before the maf (airbox, filter restriction) will have no effect on that maf

3) a restriction after the maf (intercooler, turbo, pipes) will reduce flow to that maf

4) a leak after the maf (intercooler, turbo, pipes) will reduce flwo to that maf

i cannot think of a reason why a correctly-functioning maf will flow more air - therefore you should be looking at 1,3 & 4.

however the tcu code should take precidence at this point, because it could indicate a bad ecu.

42TT

May 17th, 2007, 05:36

SKIWI: Well most of the logs have been without the airbox so that narrows it down to 3&4.

As far as the tcu code i will have a look and see if i can see any wirring problems at the ecu and tcu. I have checked the voltages for the maf on Bank1 and Bank2 and they are the same so it couldnt be the ecu casuing the maf variance but it could be causing the other issue

42TT

42TT

May 17th, 2007, 10:00

Update:

Went over all the pipes and hoses on the car and all of them seemed fine. Did another log and the maf's are still a fair way out of wack.

I cleared the tcu error and it hasnt re-appeared as yet.

SKIWI: Your comment about a faulty ecu has got me thinking could the maf variance also be caused by a faulty ecu? Also the max variance of 20% is that at any given rpm point or an overall avg of the variances?

Also

Thanks
42TT

42TT

May 17th, 2007, 15:53

TCU error has not re-appeared.

FUngusmud: As requested I logged block 032 and have attached the log.

Thanks
42TT

NB: Rename the file to .xls for viewing

FUngusmud

May 17th, 2007, 16:52

Looking at the fuel trims from block 32 make me think you have either a ECU/wiring or MAF failure. I've seen LOTS of these MAF's fail, especially when used with a non-stock filter (Oil), or if dirty air gets by the filter. I've seen them read high at idle when they go bad (and low under load, which goes against what we're seeing).

I would start by replacing the maf associated with the second MAF reading on block 32 - the one reading high. Clear the error codes afterwards, drive the car and see if the fuel trims come closer to 0. -5.5 is "okay", but alittle high for comfort. Really should be around 3 or so.

The downfall is if it doesn't fix it, you have a spare MAF to troubleshoot with or hold onto for when your MAF does fail (it will eventually).

42TT

May 17th, 2007, 16:56

FUngusmud - Is the bank that is reading wrong Bank1? I had swapped the maf's before i did this data logging so it cant be the MAF. Do the readings show that Bank1 is running lean?

And the ecu isnt recording any errors.

42TT

FUngusmud

May 17th, 2007, 17:16

OKay.. Well.. IF you're tried other MAF's and still ge the same readings, the LTFT's of -5.5 are probably okay.

BANK's don't have anything to do with MAF's. the banks are post throttle plate, which is where the individual air tracks for the MAF's get combined.

I'm not sure there is a problem. We need to see other's logs from block 2 to see if this is normal.

42TT

May 17th, 2007, 17:23

Well SKIWI and some other RS6 owners have maf readings much closer than mine at idle and higher rpm's, but as can be seen from my log's they are a fair way off but this variance as a % gets larger and smaller but i havent been able to attribute it to anything.

Regarding MB032 of bank1 and Bank2 fuel trims shouldnt they be almost identical to each other? If so it means that this problem is tracking the maf variance problem.

So if we cross the following of the list:

MAF's
Vaccum Leak

What else could it be?

Thanks
42TT

FUngusmud

May 17th, 2007, 17:42

Hi. Few things:

a) Your trims are the same. 1 and 2 are bank 1 (idle, PT) and 2,3 are bank 2. It's normal for them to be 1 or 2 percent off anyway (if they were). If we did have a engine/bank issue, it would be an seperate problem from the maf1,2 issue.

b) Could be a restricted intercooler. Maybe it was hit once, maybe it has some oil in it.

Do we know where the secondary AIR, EGR, PVC valve, etc is plumbed into this car? Maybe that stuff is only on one side, and injecting air somplace.

I would also put a link and note in the other thread you started with the logs in it indicated further info is in this thread.

42TT

May 17th, 2007, 17:51

FUngusmud - The thing that puzzles me is the fluctuation in the readings. If it was a blockage somewhere it would be more consistent wouldnt it?

The PCV valves feed off the the rear of the engine where the MAF's sit it. I have sprayed soapy water over all of those areas and it didnt make any difference.

You mentioned that the fuel trims where the same but during the drive Bank1 readings where different and stayed that way even during the idle after the drive is this normal?

Feels like im chasing my tail here with no end in sight :(

Thanks
42TT

FUngusmud

May 17th, 2007, 18:03

What field varied and by how much? If they were only varying .7 or 1.5 then that's normal and fine. even 2% is fine.

Are their 2 PVC's? Maybe swap them - one could be bad.

Still wondering how EGR, secondary air and evap gets back into the intake - one of them could have a leak or not be operating properly.

42TT

May 17th, 2007, 18:06

Secondary air and EGR is injected on the back of the head via the EGR valves i also sprayed these with no effect.

Yes there is 2 PCV's. If i was to swap them and one is bad the problem should follow the bad PCV correct?

FUngusmud

May 17th, 2007, 18:25

Ok... did some reading. Secondary air isn't going to contribute as it has it's own filter and does not suck from the intake air path. There is no EGR from what I can read.

There is PCV and EVAP going to each side. If either of those are leaking, blocked or not functioning correctly then they would cause the issue. My recommendation is find where they connect to the intake path (MAF side of turbos), disconnect them and block the intake side. Leave the PVC side open and block the EVAP tubes headed to the evap system. Run the car for a few minutes at idle and see what happens (long enough to ensure the problem would occur). Don't drive it like this as you might get some oil coming out of the PCV pipes.. It will probably throw error codes.

If that fixes it, then connect one system and see what happens. Troubleshoot from there.

42TT

May 18th, 2007, 14:58

Update (again!) - Swapped the PCV valves around and no difference problem still there. I will try removing the PCV and EVAP system and go from there.

I have also started a new post requesting other RS6 owners to post logs of MB002 of their car's so we can see what variance is normal becuase after looking at ELSAWIN it states that at idle the MAF's should read almost the same which i assume this would also be the case through the rev range. The max variance of 20% is for the turbo's from what i understood not "measured air"

Thanks again
42TT

42TT

May 18th, 2007, 17:02

Just wondering could the problem with the maf readings be causing the lack of boost in the 2000-3000rpm range? I have attached a log showing what i mean.

Thanks
42TT

O.CT USA

May 18th, 2007, 21:42

I dont think it should be related because at that low range rpm the turbo is building boost or spooling up and of course there will be some variation at the beginning.

42TT

May 19th, 2007, 06:52

OCT - I see your point but from my log from ~2100rpm to ~2500rpm my Actual Boost is a fair way off Requested Boost.

Is this normal? I can understand the ecu having the boost ceiling set high at low rpms where the turbos can spool but accoring to ELSAWIN at 2500rpm in 4th i should have full boost. Having said that not sure how much effect it has but the log shown is a 3rd gear WOT run.

42TT

FUngusmud

May 19th, 2007, 22:03

The boost deviation down there is normal for 3rd gear. 4th maybe alittle closer, but some deviation at 2500 is normal. Takes time and exhaust flow (i.e. rpm's at WOT) to build intake boost.

42TT

May 20th, 2007, 11:54

Okay,

Well i will have the car smoke tested for a vacum leak. Is there anything else than can be wrong in case no leak is found?

42TT