# High overboost due to remap: MAF gives error



## Elmbo (Nov 21, 2005)

Hi All,

IÂ´ve got a funny one for you guys. I just had my custom remap tuned a little more agressively as I was only getting about 16 psi. Now I am holding a little over 21 psi (is this to much by the way?). The car goes like a rocket.

The car is still in the "getting used to" period as the overboost when I hit the accelarator really surges the turbo and takes a bit to settle down. The funny thing is, 1 to 3rd gear no problems what so ever. However from 4th gear on, when I hit the trottle at 2500-3000 rpm and pull it to 4000-4500 or so, the engine warning light comes on. Hooking up Vag-Com reveals that the MAF gives a fault reading that to much air is going into the engine. The car also doesnÂ´t pull that well when the Turbo is surging in overboost and the N75 (which has just been replaced) hasnÂ´t regulated it back to command pressure.

I called my tuner of course and he knows this problem. I told me to drive a couple of hundred kilometer to see if the ecu (N75) adapts the overboost correctly and faster downwards and stops the maf from giving fault readings. If not, to come back to adapt the software.

I donÂ´t have a boost gauge in the car at the moment so I donÂ´t know what peak overboost is doing by the way. Vag-Com is showing me holding boost at arround 2.5 bar.

Any thoughts?


----------



## tdk (Jul 22, 2003)

Elmbo said:


> I was only getting about 16 psi. Now I am holding a little over 21 psi (is this to much by the way?).


That sounds fine - my car holds at 23 psi.

However...


> I donÂ´t have a boost gauge in the car at the moment so I donÂ´t know what peak overboost is doing by the way. Vag-Com is showing me holding boost at arround 2.5 bar.


Holy crap! 2.5 bar is just over 35 psi!    
If you keep that up the next thing you'll hear is a big BANG! 

I think I'd be heading back to the tuner ASAP. Who did you use for the remap?

Simon.


----------



## Elmbo (Nov 21, 2005)

tdk said:


> Elmbo said:
> 
> 
> > I was only getting about 16 psi. Now I am holding a little over 21 psi (is this to much by the way?).
> ...


2.5 bar is overal boost (including ambient) as displayed in Vag-Com. So that would be arround 1.5 bar (substract ambient pressure of about 1 bar). I donÂ´t think that the turbo can generate 2,5 bar boost anyway...

The question is still, how come the maf sensor gives an error...? And will it go away once the ecuÂ´s "learns" the new settings....


----------



## John-H (Jul 13, 2005)

Hi Elmer,

I was a bit worried about your boost figures until you explained it was really 1.5 BAR which sounds OK for a remap :roll:  .

Perhaps you have a faulty MAF. If it's the original I'd suspect it. They often show a fault with a remap whereas with a standard map they seem OK. I would have thought your tuner would check this out during the process but perhaps not. You could try unplugging it to see if things improve. An easy fix if that is the problem.

Did you manage to sort out your shock absorbers?


----------



## Nick225TT (Oct 13, 2004)

Elmbo said:


> tdk said:
> 
> 
> > Elmbo said:
> ...


Maybe the MAF is reporting an airflow rate that the ECU interprets as a fault. Your new map requires the engine to pull a lot of air past the MAF and the signal it is sending to the ECU it out of it's tolernace limits.


----------



## Elmbo (Nov 21, 2005)

John-H said:


> Hi Elmer,
> 
> I was a bit worried about your boost figures until you explained it was really 1.5 BAR which sounds OK for a remap :roll:  .
> 
> ...


Hi John,

The tuner checked the MAF, DV, N75 etc. and did not really find any faults (only the N75 which we replaced). It is showing readings around 200 in Vag-Com at full rpm. Which would indicate that it should be ok, or not?

Shocks have not been sorted out yet. That part number on the shocks does not correspond to one of the numbers you emailed me.. Will have to have a further look at it..


----------



## Elmbo (Nov 21, 2005)

Nick225TT said:


> Elmbo said:
> 
> 
> > tdk said:
> ...


That is what my tuner told me. He also said that as the engine regulates itself in the first few hundred kilometer the problem could simply go away as the N75 will learn to limit overboost in a much better way... If it didnÂ´t he would need to adapt the custom map slightly.


----------



## Elmbo (Nov 21, 2005)

tdk said:


> Elmbo said:
> 
> 
> > I was only getting about 16 psi. Now I am holding a little over 21 psi (is this to much by the way?).
> ...


By the way. IÂ´m located in The Netherlands... So my tuner was Hartog Tuning. He is one of the 2 best guys in the country for custom tuning in NL. Especially for the VAG 1.8T engine. He really knows his stuff and gives fantastic service... I actually asked him to give me an agressive map which wold of course not damage the engine...


----------



## Elmbo (Nov 21, 2005)

This is the message I get in Vag-Com:
*****************
Control Module Part Number: 8N0 906 018 AE 
Component and/or Version: 1.8L R4/5VT G 0001
Software Coding: 05710
Work Shop Code: WSC 00000
1 Fault Found:
16487 - Mass Air Flow Sensor (G70): Signal too High
P0103 - 35-10 - - - Intermittent
*****************

I also just did a plot in Vag-Com and noticed something interesting in the 4th gear plot:

***
Engine Speed	Cmd Pressure	Press @ Intercool
% mbar mbar
2720	2540	1850
3160	2300	2450
3640	2240	2500
4040	2200	2480
***

I notice that command pressure is much lower than the actual pressure in 4th gear. I don't see this at all in the 1st to 3rd gear numbers. Could this be causing the error? Ik looks like the N75 isn't regulating fast enough (yet?).

look foward to your thoughts...


----------



## Elmbo (Nov 21, 2005)

Come on guys, somebody Â´s got to have an opinion on this...


----------



## John-H (Jul 13, 2005)

Hi Elmer,

I'm not sure I understand the last block of figures. Are you saying the turbo seems to be overboosting more in 4th gear and not being regulated? That's odd if it happens in 4th as you'll be in 4th for longer giving more time for the system to adjust - I don't follow the give it time to learn comment. You should not be generating fault codes during the learning process. Did you reset the ECU?

You also have too high an airflow fault code. Usually the MAF fails outputting too low an airflow so the mixture goes lean on wide open throttle giving you poor acceleration. Often this doesn't show as a fault until it gets really bad. If your MAF is outputting too high an airflow it would tend to make the ECU run rich. I would have thought the fault code is generated on an "implausible" signal e.g. if it went high and stayed there too long despite other engine conditions - like being at idle. I'm not sure if it's more subtle than this and references the lambda sensor during steady state running for example.

I also would have thought that if you were overboosting it wouldn't generate a MAF airflow fault but rather a manifold pressure fault or torque limit, or N75 if it didn't think it was regulating.

It might still be worth running without the MAF connected to see if the overboost problem changes - obviously you'd get a MAF failed fault with it disconnected.


----------



## Elmbo (Nov 21, 2005)

John-H said:


> Hi Elmer,
> 
> I'm not sure I understand the last block of figures. Are you saying the turbo seems to be overboosting more in 4th gear and not being regulated? That's odd if it happens in 4th as you'll be in 4th for longer giving more time for the system to adjust - I don't follow the give it time to learn comment. You should not be generating fault codes during the learning process. Did you reset the ECU?


More or less. So the turbo provides more pressure than the ecu is asking for. In lower gear I beleive the revs climb quickly enough that the pressure drops faster higher up the rev range so the overboost is much shorter. In 4th gear or up, the revs climb much slower and somehow the turbo is overboosting (strong whooshing sound is hearable) much longer causing the error... ECU was reset automatically when new software was loaded (or not?)



> I would have thought the fault code is generated on an "implausible" signal e.g. if it went high and stayed there too long despite other engine conditions - like being at idle. I'm not sure if it's more subtle than this and references the lambda sensor during steady state running for example.


I'm not sure what you mean by this..



> I also would have thought that if you were overboosting it wouldn't generate a MAF airflow fault but rather a manifold pressure fault or torque limit, or N75 if it didn't think it was regulating.


It generates just the MAF error..



> It might still be worth running without the MAF connected to see if the overboost problem changes - obviously you'd get a MAF failed fault with it disconnected.


I've already tried this. Makes no difference in how the car drives... You still hear the overboost air rushing (strong wooshing sound) at arround 2800-4000 rpm


----------



## John-H (Jul 13, 2005)

Elmbo said:


> John-H said:
> 
> 
> > Hi Elmer,
> ...


I see how you think the turbo may be getting the time to overboost in 4th. That seems to imply there is no control and it's running away i.e. in 4th there should be time for the system to control it but it doesn't.

The wooshing sound was the first thing I noticed about my remap - but it starts around 2000rpm for me in 4th gear and gets masked by the engine note well before 4000 rpm. I had performance right from the start or the remap, no errors and no period of learning as far as I could tell. I thik the learning after a reset is firstly to do with ignition advance before pinking.



Elmbo said:


> > I would have thought the fault code is generated on an "implausible" signal e.g. if it went high and stayed there too long despite other engine conditions - like being at idle. I'm not sure if it's more subtle than this and references the lambda sensor during steady state running for example.
> 
> 
> I'm not sure what you mean by this..


I mean that I think fault codes are generated when the ECU thinks the signal from a sensor is clearly incorrect e.g. always high or always low when it should go up and down etc. The ECU could be clever and look at the lambda (oxygen) sensor in the exhaust and work out, that although the MAF signal is varying (and not stuck) the MAF signal is, however, a little too high or too low in reference to the lambda sensor.

The lambda switches as the mixture goes slightly rich (no oxygen) or lean (some oxygen) so is an absolute benchmark to complete combustion. Couple that to the injector pulse time (amount of metered petrol) used to maintain the lambda at the switching threshold and it would be possible to estimate the airflow to go with it. The ECU could see how far out it's estimate of airflow was from the MAF signal and throw an error if there was a mismatch. It could only do this at steady state e.g. cruising or slow acceleration. I'm speculating and don't know if the ECU is that clever.



Elmbo said:


> > I also would have thought that if you were overboosting it wouldn't generate a MAF airflow fault but rather a manifold pressure fault or torque limit, or N75 if it didn't think it was regulating.
> 
> 
> It generates just the MAF error..
> ...


Isn't that saying that it's not the MAF that's causing the problem? With the MAF removed the mixture is set slightly rich for open throttle acceleration in order to be safe (as opposed to working from the MAF signal). Most MAFs fail giving a low airflow reading fooling the ECU into running a lean mixture - that's why removing such a failed MAF restores performance.

Perhaps your MAF has failed the other way but that's less likely. You say it makes no difference with it unplugged. It was worth a try and it helps to know the result.

As you have had the N75 replaced I'm wondering if you have a hose leak. Perhaps this might tie in with the noise and the higher than expected airflow. Perhaps the ECU does reference the lambdas and can't understand where the air has gone that the MAF is reporting so is throwing a too high a MAF reported airflow? That would be less likely to be seen in lower gears as it's too far off steady state for the lambdas to be referenced.

This is speculation on my part as I'm not 100% sure how the ECU decides a MAF fault code... BUT... blown off and split hoses are seen after remaps due to the higher pressure suddenly in the system. This seems to tie in. Might be worth an inspection of the big hoses after the turbo :wink:


----------



## Elmbo (Nov 21, 2005)

Hi John,

Thanks for your elaborate reply. Bit of a strange case it seems... My feeling is that the MAF is fine. I've done quite a few vag-com plots and the MAF numbers look like they are what they should be.. Couls indeed be something to do with the Lambda. U've looked at the lambda numbers before and they looked a bit funny to me. But as you say, at WOT the ecu does not look at the Lambda numbers as far as I know...

I'll have a look at all the hoses that are connected to see if anything has gobe wrong there.. I only find it funny that I don't get any arrors in the first 3 gears and the engine pulls like a mule...

I've talked to my tuned and he told me to come back and he'd have a good look at everything including the software. He said it's possible that, as it's an agressive map, and every car/turbo is different, this map is a bit to agressive for this car and would need to adapt the software slightly. he also mentioned e wanted to have a look at the waste gate as it might nog be working optimally (do you think this is possible?).

Cheers,

Elmer


----------



## John-H (Jul 13, 2005)

If it works OK in all the other gears perhaps it's not a hose come adrift or if it is perhaps it's only a slight leak that only shows up in 4th where there's longer time involved. Wastegate perhaps - could be? The lambda readings don't make much sense when logging because the sensor is constantly switching up and down 0.5V between 0.2V and 0.7V two or three times a second when cruising and the logging rate is only 3 times a second or so, so it depends where it catches it. It's only useful to see it is going up and down and functioning. The best way to look at Lambdas is using an oscilloscope - then you should see a nice square wave.


----------



## Elmbo (Nov 21, 2005)

John-H said:


> The lambda readings don't make much sense when logging because the sensor is constantly switching up and down 0.5V between 0.2V and 0.7V two or three times a second when cruising and the logging rate is only 3 times a second or so, so it depends where it catches it. It's only useful to see it is going up and down and functioning. The best way to look at Lambdas is using an oscilloscope - then you should see a nice square wave.


Aha, that explains that!



> If it works OK in all the other gears perhaps it's not a hose come adrift or if it is perhaps it's only a slight leak that only shows up in 4th where there's longer time involved. Wastegate perhaps - could be?


IÂ´m going back to the tuner coming monday. He told me he would sort it out. Good to know that he has the highest VAG mechanic qualifications...


----------



## John-H (Jul 13, 2005)

I'm sure you'll get it sorted. Interesting problem. I'd be interested in knowing the solution.

Cheers,

John


----------



## Die666 (Jun 19, 2007)

John-H said:


> I'm sure you'll get it sorted. Interesting problem. I'd be interested in knowing the solution.
> 
> Cheers,
> 
> John


So do i...


----------



## freegeek (Aug 26, 2005)

Elmbo
The tuner checked the MAF said:


> That maf reading looks much too low for the boost you are running. :?


----------



## Die666 (Jun 19, 2007)

freegeek said:


> Elmbo said:
> 
> 
> > The tuner checked the MAF, DV, N75 etc. and did not really find any faults (only the N75 which we replaced). It is showing readings around 200 in Vag-Com at full rpm. Which would indicate that it should be ok, or not?
> ...


i get 200 with a 1.2->1.4 boost.
Almost the same with a 1.5bar boost.


----------



## Black Knight (Jan 16, 2007)

Does the 1.8T have a wideband lambda sensor? The ECU will not be able to check MAF signal against lambda signal at WOT unless it's a wideband lambda. At WOT the ECU is seriously overfueling and the regular lambda sensors can't read that. They're only precise at near stoichiometric ratio.

Still I doubt the ECU even touches the lambda signal at WOT. He reported that the ECU logs an error only after he WOTs in 4th or higher gear. Which means the MAF is operating in "acceptable" range when not in WOT at higher gears.

My guess would be a leaking pipe intake manifold->solenoid->wastegate actuator.. or a faulty solenoid.

Is N75 the solenoid valve(the one that lets the ECU trick the wastegate actuator into thinking manifold pressure is lower than it is)? I'm not familiar with the 1.8T but I've had my share of turbo engines


----------



## Die666 (Jun 19, 2007)

Black Knight said:


> Does the 1.8T have a wideband lambda sensor? The ECU will not be able to check MAF signal against lambda signal at WOT unless it's a wideband lambda. At WOT the ECU is seriously overfueling and the regular lambda sensors can't read that. They're only precise at near stoichiometric ratio.


Depends on the motor Type, BAM has no wideband, APX does.



Black Knight said:


> Is N75 the solenoid valve(the one that lets the ECU trick the wastegate actuator into thinking manifold pressure is lower than it is)? I'm not familiar with the 1.8T but I've had my share of turbo engines


Yes it is.


----------



## Black Knight (Jan 16, 2007)

Well then perhaps they didn't connect it up properly? This is why I've grown to hate turbo engines.. aside from the lag.. there's so much stuff that can cause weird behaviour.. very hard to diagnose.. collapsing pipes only collapse under boost, not when you look at them.. hair cracks only open up under boost, not when you look at them.. blah blah.. I got myself a V6 

One of my ex turbos actually had a hole the size of a thumb in the piping after the turbo.. and it actually worked normally...aside from the fact I could hear a lot of wooshing.. I can't really imagine how it worked.. boost should leak out but it actually managed to boost properly.. at idle unmetered air should be sucked in and confuse it and it idled normally... turbo engines are weird


----------



## John-H (Jul 13, 2005)

Die666 said:


> Black Knight said:
> 
> 
> > Does the 1.8T have a wideband lambda sensor? The ECU will not be able to check MAF signal against lambda signal at WOT unless it's a wideband lambda. At WOT the ECU is seriously overfueling and the regular lambda sensors can't read that. They're only precise at near stoichiometric ratio.
> ...


Early TTs had narrowband sensors, such as my APX but later ones had wideband sensors and sensors before and after the cat.

Anyway guys, nobody seems to have noticed, or perhaps they have, that this thread was started in June 2006 not 2007 and I expect Elmer has sorted his problems by now but I notice he hasn't posted since January this year :? . I'll send him an email to see what's happened over this problem :wink: .


----------



## Elmbo (Nov 21, 2005)

Hi Guys,

Well noted that I havent posted for a while. Still trying to get over that I had to sell my TT in January....

If I remember well, my turbo was giving to much boost. The sucking sound was also very weird. The tuner changed the map an lowered the boost and problem solved. No more errors from the MAF and the weird sucking sound was gone as well. So If you have the same symptoms, lowering the turbo+s boost could solve it for you.

My car did pull like a mule once adapted.

cheers,

Elmer


----------



## Black Knight (Jan 16, 2007)

buh, what a disappointing update


----------



## Elmbo (Nov 21, 2005)

Black Knight said:


> buh, what a disappointing update


What? the fact I sold the TT or that you need to reduce boost to get rid of the problem?

If itÂ´s the first: dissapointing indeed. I did get a volvo S60 D5 tuned to 226 HP and 340 lb/ft of torque as a replacement by the comany I work for...

If its the latter: my car was going up to about 1.7 bars of boost which in my opinion will kill it in the long run. After the tuner adapted it it maxed out between 1.4 and 1.5 bar, which is plenty...


----------



## Black Knight (Jan 16, 2007)

well, both 

you sold the TT, that's disappointing for sure :/

the conclusion that you need to lower boost because MAF gives error is somewhat vague.. what if you modified internals of the engine or whatever, put on water injection.. modify the engine so it can take the 1.7 bar boost, what then? is that the limit of the OEM MAF sensor or the ECU? how do people then get 450hp out of it? do they replace the ECU with aftermarket engine management stuff? or just the MAF? or perhaps the tuner simply isnt as good as you think he is and he messed up a perfectly good remap when you asked him to turn up to boost a bit :/ maybe it's not that simple as he thought..

anyway, many questions remain  and that's too disappointing


----------



## John-H (Jul 13, 2005)

Most people get higher powers of that order by putting a bigger turbo on. If you overboost the standard one it will run out of steam at high engine rpm, so limiting the useful power band to mid range and its lifetime will reduce. People have used manual boost controllers and got carried away, ending in blown turbos and scrap engines :?


----------



## Die666 (Jun 19, 2007)

Black Knight said:


> well, both
> 
> you sold the TT, that's disappointing for sure :/
> 
> ...


My first remap was about 1.6 i think. But it was cutting, going to limp mode.. etc.. 
Now we dramatically reduced the pressure, and it's almost like the original :/
He uses race2000, from dimsport, and the annoying thing is that you can't say " iwan't 1.4bar" , it's all about coefficient. You can choose between 6000 and 10000 .. Which value corresponds to 10000 .. dunno.. and he doesn't know too :/


----------



## Black Knight (Jan 16, 2007)

John-H said:


> Most people get higher powers of that order by putting a bigger turbo on. If you overboost the standard one it will run out of steam at high engine rpm, so limiting the useful power band to mid range and its lifetime will reduce. People have used manual boost controllers and got carried away, ending in blown turbos and scrap engines :?


bigger turbo doesn't matter.. no reason why a bigger turbo would help with the MAF error?


----------



## Elmbo (Nov 21, 2005)

Die666 said:


> Black Knight said:
> 
> 
> > well, both
> ...


Sounds like you have a tuner that doesnÂ´t quite know what heÂ´s doing... Mine had a kind of graph where he could adapt values by change things in the graph....


----------



## John-H (Jul 13, 2005)

Black Knight said:


> John-H said:
> 
> 
> > Most people get higher powers of that order by putting a bigger turbo on. If you overboost the standard one it will run out of steam at high engine rpm, so limiting the useful power band to mid range and its lifetime will reduce. People have used manual boost controllers and got carried away, ending in blown turbos and scrap engines :?
> ...


Some confusion here... 2.5Bar was quoted earlier but that was absolute and not boost which was nearer 1.5Bar. There was slight overboosting to 1.7Bar boost, which was possibly causing the ECU to throw things into limp mode and the MAF was merely reporting the higher airflo - but I was actually just answering your question about how people get 450bhp etc and that's not by changing the MAF or ECU but changing the turbo to a bigger one. Just winding up the original will run into problems - generally speaking.


----------



## 225 TTC (Jan 26, 2007)

very interesting read!

round of aplause for john h and black knight, u really know your stuff! :wink:


----------



## Black Knight (Jan 16, 2007)

i dont really know much, just read a lot of technical articles and forums(usually trying to diagnose my problems) and like to talk about this stuff  
and also had quite a few troublesome cars :?

john-h knows his stuff, that's for sure!


----------



## John-H (Jul 13, 2005)

Black Knight said:


> i dont really know much, just read a lot of technical articles and forums(usually trying to diagnose my problems) and like to talk about this stuff
> and also had quite a few troublesome cars :?
> 
> john-h knows his stuff, that's for sure!


But that's what I do too :lol:


----------

