MAF readings discrepancies

   #1  

Classik

Verified VCDS User
Verified
Joined
Mar 26, 2019
Messages
26
Reaction score
2
Location
France
VCDS Serial number
C?ID=355804
Hi all,

I've been chasing my tail for a while with a very strange MAF discrepancy issue between bank1 and 2 on my car (Audi RS6 C5 2003), so I'm now looking for guidance from the bright minds.

Symptoms are that - as seen on the advanced measuring values on my Hexnet- as long as the engine temp (coolant) stays below 80°C, readings on both MAFs are perfectly aligned within a 5-7% margin, but above 80°C, value of maf bank 1 starts to decrease little by little compared to bank 2. When the engine reaches a stable temperature (90-95°C), the discrepancies between banks are as high as 70%, and like 40-50% when idle... Of course I get a fault code on the engine ECU (and that's the only one) saying I have implausible MAF discrepancy : '17416 - Mass Air Flow Sensor 1/2 : Implausible Signal - P1008 - 004 Intermittent'.
To cut a long story short, I've already checked all hoses (including vaccum hoses) and seals, swapped the MAFs (same readings), checked the SAI valves/system, changed the EVAP solenoid (N80), along with the N112 and N249, without success. A quick air pressure leak test on the air inlets didn't show anything to worry about...

Sooo after chasing a physical/mechanical problem (maybe it's still the case!), I start to wonder whether something could be wrong with the control /electrical system, like - off the top of my head - the engine ECU not receiving correctly the temperature sensor of one of the MAFs for gaz expansion compensation. Would that explain the strange and slow shift around 80°C? Could a faulty ECU remap create such a phenomenon (my car is remapped but rewriting the stock map didn't change anything, except performance) ? Still scratching my head on this issue, so any help/suggestion is welcome!
Best
 
Last edited:
   #2  

Larry Manton

Verified VCDS User
Verified
Joined
May 19, 2016
Messages
813
Reaction score
407
Location
USA
VCDS Serial number
C?ID=112505
CLASSIC, okay most mostly a TDI guy but As I see it. Cold engine might be tighter then as warms tolerances fade. That is making assumption each bank has its own MAF, could be wrong.

Would be looking at compression check. As have no scan DON'T
know mileage wear factor here?

Would suspect one bank not as efficient as the other, just an opinion.

Also post an auto scan as you will be requested to do so as were only as brite as the info we have?

Good hunting

LARIMORE
 
   #3  

Uwe

Benevolent Dictator
Administrator
Joined
Jan 29, 2014
Messages
48,925
Reaction score
33,652
Location
USA
VCDS Serial number
HC100001
So even with the MAFs swapped, the problem (lower readings at higher temperatures) remain on Bank 1?

Have you considered the the possibility of some wiring problem or connection that has a resistance change with temperature? Perhaps a dodgy ground connection on one side?

-Uwe-
 
   #4  

Jack@European_Parts

Gone But Not Forgotten
Professional VCDS User
Joined
Jan 29, 2014
Messages
21,923
Reaction score
9,308
Location
Montgomery, NY, USA
VCDS Serial number
C?ID=57337
I start to wonder whether something could be wrong with the control /electrical system, like - off the top of my head - the engine ECU not receiving correctly the temperature sensor of one of the MAFs for gaz expansion compensation. Would that explain the strange and slow shift around 80°C? Could a faulty ECU remap create such a phenomenon (my car is remapped but rewriting the stock map didn't change anything, except performance) ? Still scratching my head on this issue, so any help/suggestion is welcome!


Who is the tuner?

FOD!
https://forums.ross-tech.com/showth...essional-Problem-Solver-Guide-quot-JPPSG-quot

Remap most likely causing problem or not reporting the entire story in stack.

fod-control-signs-risk-series.png
 
   #5  

Classik

Verified VCDS User
Verified
Joined
Mar 26, 2019
Messages
26
Reaction score
2
Location
France
VCDS Serial number
C?ID=355804
Thank you for replies and suggestions! I checked the wiring and admittedly with theses cars the MAF connectors are never in great shape due to the VERY small space behind the engine. So yes this may well be a reason. All main grounding points have been checked and cleaned no later than last Wednesday, so we should be covered.. except if the wiring doesn't follow of course.
However I'm puzzled to hear an impedance dependancy to temp but you guys know better than me.

Mapper is CTF Performance (in France-serious people), but as we speak I'm running the stock map (got an external device which allows to write map at will). Does that help?
 
   #6  

Jack@European_Parts

Gone But Not Forgotten
Professional VCDS User
Joined
Jan 29, 2014
Messages
21,923
Reaction score
9,308
Location
Montgomery, NY, USA
VCDS Serial number
C?ID=57337
You mean switched or completely re flashed?

Most of time if not complete reflash the nefarious tasks still exist in most tuners alleged but not actually a stock map.
 
   #7  

Classik

Verified VCDS User
Verified
Joined
Mar 26, 2019
Messages
26
Reaction score
2
Location
France
VCDS Serial number
C?ID=355804
I meant completely reflashed, the whole process takes like 10 minutes.
The map is supposed to be an oem map, but how could I know for sure..
Is there a way to check if the MAFs readings have been changed / tricked in any way?
Many thanks!
 
   #8  

Jack@European_Parts

Gone But Not Forgotten
Professional VCDS User
Joined
Jan 29, 2014
Messages
21,923
Reaction score
9,308
Location
Montgomery, NY, USA
VCDS Serial number
C?ID=57337
Not VCDS related.

Install known stock parts, perform repairs as per RTFB using VCDS blocks, codes reported and with aid of mechanical and electronic testing equipment such as load light and DVOM.
 
   #9  

Classik

Verified VCDS User
Verified
Joined
Mar 26, 2019
Messages
26
Reaction score
2
Location
France
VCDS Serial number
C?ID=355804
Install known stock parts, perform repairs as per RTFB using VCDS blocks, codes reported and with aid of mechanical and electronic testing equipment such as load light and DVOM.

I can only concur with the above, wise recommandations of course, particularly the electrical circuit check.

Not VCDS related.

Sorry but I don't fully understand. Mind expanding on that? Thank you!
 
   #11  

Classik

Verified VCDS User
Verified
Joined
Mar 26, 2019
Messages
26
Reaction score
2
Location
France
VCDS Serial number
C?ID=355804
From the tone of your reply I clearly must have missed something. Is that a forum rule not to talk about remaps, or have shown disrespect? :confused:

Of course you don't have to reply, but my understanding is that MAFs readings in g/s as seen in VCDS are a calculation based on the signals sent by the MAF, so were you implying VCDS don't have access to these 'lower level' calculations, like a program on any computer don't have access to the underlying Operating System operation?
 
   #12  

Classik

Verified VCDS User
Verified
Joined
Mar 26, 2019
Messages
26
Reaction score
2
Location
France
VCDS Serial number
C?ID=355804
CLASSIC, okay most mostly a TDI guy but As I see it. Cold engine might be tighter then as warms tolerances fade. That is making assumption each bank has its own MAF, could be wrong.

Would be looking at compression check. As have no scan DON'T
know mileage wear factor here?

Would suspect one bank not as efficient as the other, just an opinion.

Also post an auto scan as you will be requested to do so as were only as brite as the info we have?

Good hunting

LARIMORE

Missed your post Larry, thank you. Yes I have 2 MAF, one per bank. Good point, but wouldn't that efficiency mismatch be seen somewhere down the line, I don't know like injectors duty cycles or lambda readings (the latter are perfectly matched by the way)?

Regarding the full auto scan, I'll definetely comply to the rule (away from home for a week or so, but will be done on my return), but as the only engine fault code is this MAFs mismatch I though appropriate (probably wrongly) not to bother with the rest.
 
   #13  

Jack@European_Parts

Gone But Not Forgotten
Professional VCDS User
Joined
Jan 29, 2014
Messages
21,923
Reaction score
9,308
Location
Montgomery, NY, USA
VCDS Serial number
C?ID=57337
Okay look at it this way.
VCDS can only see what the controller permits it too.
If hardware or in this case the ECU is remapped than the data that is or isn't displayed would be foolish to rely on.

The RTFB is a guide for an unmodified vehicle, therefore care and specs of the mods would be wise to ref.
There are no substitutions for actual mechanical or electrical tests.

OBD data is a guide, not a single catch all for doing proper repairs stock or modified. A cross check of data or hardware is REQUIRED and advised when seeking proper repairs.
 
   #14  

Classik

Verified VCDS User
Verified
Joined
Mar 26, 2019
Messages
26
Reaction score
2
Location
France
VCDS Serial number
C?ID=355804
Okay look at it this way.
VCDS can only see what the controller permits it too.
If hardware or in this case the ECU is remapped than the data that is or isn't displayed would be foolish to rely on.

The RTFB is a guide for an unmodified vehicle, therefore care and specs of the mods would be wise to ref.
There are no substitutions for actual mechanical or electrical tests.

OBD data is a guide, not a single catch all for doing proper repairs stock or modified. A cross check of data or hardware is REQUIRED and advised when seeking proper repairs.

Thanks for taking the time, appreciated. So to be clear I need to double/tripple check with my mapper that the supposed OEM map is indeed correct before chasing my tail on this issue. Makes totally sense, but in my defense I wouldn't have even envisaged their OEM map could be faulty. Need to educate myself about the difference between switched map vs reflashed map, so take my former response with a full spoon of salt..
 
   #15  

Jack@European_Parts

Gone But Not Forgotten
Professional VCDS User
Joined
Jan 29, 2014
Messages
21,923
Reaction score
9,308
Location
Montgomery, NY, USA
VCDS Serial number
C?ID=57337
Get real second factory test ecu or file than compare binaries to see if consistent with each other.

You may enjoy this link.
www.evc.de
 
   #18  

Classik

Verified VCDS User
Verified
Joined
Mar 26, 2019
Messages
26
Reaction score
2
Location
France
VCDS Serial number
C?ID=355804
   #19  

Jack@European_Parts

Gone But Not Forgotten
Professional VCDS User
Joined
Jan 29, 2014
Messages
21,923
Reaction score
9,308
Location
Montgomery, NY, USA
VCDS Serial number
C?ID=57337
I've just read the first 10 posts, sounds promising :popcorn:
For that matters sai and evap are fully operational here, admittedly reduced cats (200 cells) but most of the time I'm running on e85, except when troubleshooting my MAFs discrepancies issue.. ;)


So you have drank the Kool-aid......? :p

The difference between "True Motorsports" and just delete or defeat devices is where you have to consider is the SMOG device really hindering an alleged performance characteristic or is it that someone can't tune or is lazy and they direct you to delete it & because they set a control table to ZERO?

No real rocket science to setting stuff to zero huh, is that to be respected?


I guess my question to you and any of the tuners is, if the engine is running allegedly more efficient after one of these tunes and with harmonious combustion, why would you have to delete the CAT or readiness monitors and if you didn't remove the physical CAT, why would the CAT exhibit shortly after such a tune & at a 99% failure RATE on an actual factory CAT & being completely damaged, restricted or plugged?
 
Last edited:
   #20  

Uwe

Benevolent Dictator
Administrator
Joined
Jan 29, 2014
Messages
48,925
Reaction score
33,652
Location
USA
VCDS Serial number
HC100001
From the tone of your reply I clearly must have missed something. Is that a forum rule not to talk about remaps, or have shown disrespect? :confused:
No, there is no such forum rule. That's just Jack being Jack.

Now remaps do make trouble-shooting more difficult. I've seen it myself where a car with stock software ran pretty well, but "tuned", it was horrible, and the source of this was eventually traced to a small vacuum leak. So a "mapped" ECU can behave quite a bit differently. In addition, some tuners seem to think it's necessary or desirable to disable certain tests for faults...

Of course you don't have to reply, but my understanding is that MAFs readings in g/s as seen in VCDS are a calculation based on the signals sent by the MAF, so were you implying VCDS don't have access to these 'lower level' calculations, like a program on any computer don't have access to the underlying Operating System operation?
Those calculations -- turning analog sensor readings into something resembling real-world values like g/s -- are done by the ECU, not VCDS. Now the digital value that the ECU sends to VCDS may still not be g/s, but that conversion will be some well-understood formula that isn't likely to be wrong, especially on 2003 car.

-Uwe-
 
Back
Top