Wastegate Test

[elaw]

Guys,

If he disconnected the N75 (electrically) and got low boost, that indicates the N75 and WG are plumbed and working properly.

Therefore the command to increase boost is coming from the computer and the question is why? The "MAP sensor not seeing the boost pressure" theory makes sense... I'm not sure what can be done to test that other than making sure all tubing etc. is connected properly and not cracked or broken. Is there any way to read what the MAP sensor is seeing with a VAG-COM or something?

[UrS4boy]

G71 Manifold Absolute Pressure (MAP) sensor information

Is there any way to read what the MAP sensor is seeing with a VAG-COM or something?

Yup. See below:

G71 Manifold Absolute Pressure (MAP) sensor information

http://forums.quattroworld.com/s4s6/msgs/20417.phtml

[BosnianS2]

So I had some time yesterday and today to continue to find out what the heck is going on with my boost so here is update on what I did.
First i checked the line that goes from intake manifold to ECU follwong way: I disconnected the line from inkate manifold and using hand vacuum pump i pulled vacuum and it held, so that means this line is good however i thought what if it had blockage, so then i disconected the line from ECU also and using compressed air blew through and it checked ok, air was goung through.

Then to make sure 100% i temporarily connected the ECU to intake manifold using a long piece of new vacuum line ( routed through window) and test drove, problem unfortunaltely was still there, boost 2 bar and missfiring.

Then I said f..k it i took the chips out and installed the original chips back in and test drove the car. So this time the missfire was gone, car pulls good but still it goes to 1,5-1.6 Bar, so that means problem with boost controll ist still there.

Then I started to question my boost gauge, so i borowed one and T-it in by ECU. Test drove again and this second gauge shows also same situation, 1,5-1.6 Bar which means that my gauge is correct.

Only good news is that missfire ist completely gone with original software and apparently ECU is managing this extra boost at stock level and that wy the car pulls good now.

I guess now what I need to to is take the above advice and remove wastegate and check if its sticking, however when i remowed the cover from wastgate few weeks ago to inspeckt the membrane visually the valve was movin very smoothly and easy.

I am runing out of ideas now, but i will go ahead and take it off now and take closer look

PS. No codes in ECU

[BosnianS2]

I took the VCDS to look at this value of MAP sensor that was mentioned above, and here ist what i have :954,8 mbar and this value does not change as the engine is reved up.

However are we sure that this is MAP sensor value and not Altitude sensor value?

[Thecrispynoodle]

So I had some time yesterday and today to continue to find out what the heck is going on with my boost so here is update on what I did.
First i checked the line that goes from intake manifold to ECU follwong way: I disconnected the line from inkate manifold and using hand vacuum pump i pulled vacuum and it held, so that means this line is good however i thought what if it had blockage, so then i disconected the line from ECU also and using compressed air blew through and it checked ok, air was goung through.

Then to make sure 100% i temporarily connected the ECU to intake manifold using a long piece of new vacuum line ( routed through window) and test drove, problem unfortunaltely was still there, boost 2 bar and missfiring.

Then I said f..k it i took the chips out and installed the original chips back in and test drove the car. So this time the missfire was gone, car pulls good but still it goes to 1,5-1.6 Bar, so that means problem with boost controll ist still there.

Then I started to question my boost gauge, so i borowed one and T-it in by ECU. Test drove again and this second gauge shows also same situation, 1,5-1.6 Bar which means that my gauge is correct.

Only good news is that missfire ist completely gone with original software and apparently ECU is managing this extra boost at stock level and that wy the car pulls good now.

I guess now what I need to to is take the above advice and remove wastegate and check if its sticking, however when i remowed the cover from wastgate few weeks ago to inspeckt the membrane visually the valve was movin very smoothly and easy.

I am runing out of ideas now, but i will go ahead and take it off now and take closer look

PS. No codes in ECU

Surely everything still points at MAP sensor gone bad? Especially given no overboost condition / fuel cut detected by the ECU? Seems whatever software you run you are consistently hitting about .3 bar over the ECUs target.

[UrS4boy]

I took the VCDS to look at this value of MAP sensor that was mentioned above, and here ist what i have :954,8 mbar and this value does not change as the engine is reved up. However are we sure that this is MAP sensor value and not Altitude sensor value?

You can not make any boost with the car sitting in neutral so I am not sure. Can you find this screen (from the Ross-Tech website):

[BosnianS2]

Surely everything still points at MAP sensor gone bad? Especially given no overboost condition / fuel cut detected by the ECU? Seems whatever software you run you are consistently hitting about .3 bar over the ECUs target.

That is what it seems to be going but it is not easy to pinpoint what is going on. Is it possible to buy MAP sensor by itself?

[BosnianS2]

You can not make any boost with the car sitting in neutral so I am not sure. Can you find this screen (from the Ross-Tech website):

I agree that it is not possible to make boost without driving, however since ECU measures to relatively fine exent, value should change little bit ( if this is the MAP value at all) because reving up the engine cause the vacuum changes as throttle opens.

However I did some searching online ant S2Central has nice explanation of all measuring blocks for ABY, which should be same as ADU or at least very similar and value 4 at group 002 is the ambient atmospheric pressure which would explain why it does not change at all with engine running. Sadly it seems that we can not read what MAP sensor reads using VCDS

I guess if i dont find anything else, I may have to go ahead and change MAP sensor just to make sure, I dont seem to have other choice

[UrS4boy]

3 Bar MAP sensor alternative

I guess if i dont find anything else, I may have to go ahead and change MAP sensor just to make sure, I dont seem to have other choice

EFI express has this more or less, plug and play, 3 Bar sensor (an upgrade if you still have the 2.5 Bar (250 kPa) one). Would allow Stage 1+ or "RS2 (plus)" software, as appropriate:

http://www.efiexpress.com/catalog/pr...products_id=82

[Thecrispynoodle]

EFI express has this more or less, plug and play, 3 Bar sensor (an upgrade if you still have the 2.5 Bar (250 kPa) one). Would allow Stage 1+ or "RS2 (plus)" software, as appropriate:

http://www.efiexpress.com/catalog/pr...products_id=82

He will need to replace with whatever MAP sensor rating the software expects to be there which hopefully (but not necessarily) is the same as what is already fitted. In theory RS2 boost level software will be configured for a 3 bar sensor?

[UrS4boy]

G71 Manifold Absolute Pressure (MAP) sensor information

1. He will need to replace with whatever MAP sensor rating the software expects to be there which hopefully (but not necessarily) is the same as what is already fitted.
2. In theory RS2 boost level software will be configured for a 3 bar sensor?

1. Agree that the MAP sensor and the software needs to be compatible. However, I did HINT very strongly that this would be the time to go for a Stage 1+ chips set if he is still running a 250 kPa MAP sensor and either stock or Stage 1 software.

EFI express has this more or less, plug and play, 3 Bar sensor (an upgrade if you still have the 2.5 Bar (250 kPa) one). Would allow Stage 1+ or "RS2 (plus)" software, as appropriate.

2. 3Bs had OE 200 kPa MAP sensors. AANs and ABYs had OE 250 kPa MAP sensors. ADUs in RS2s had 300 kPa (3 Bar) MAP sensors. As a result, RS2 (plus) software will already assume a 3 Bar MAP sensor.

G71 Manifold Absolute Pressure (MAP) sensor information:

http://forums.quattroworld.com/s4s6/msgs/20417.phtml

[mike74]

Before ripping stuff out of the ECU to replace it, have you checked the basics yet eg: fuel pressure + flow, clean fuel filter, spark plugs + gap and injectors spraying ok?
My last car popped and misfired at higher boost which I also thought was boost control/leak or ignition. Turned out to be blocked injectors!

[Thecrispynoodle]

Before ripping stuff out of the ECU to replace it, have you checked the basics yet eg: fuel pressure + flow, clean fuel filter, spark plugs + gap and injectors spraying ok?
My last car popped and misfired at higher boost which I also thought was boost control/leak or ignition. Turned out to be blocked injectors!

Car is overboosting, hence focus on N75, wastegate, MAP sensor etc.