RS2 - Boost issue - peak at only 1 Bar

[wowow]

Gauge shows peak of only 1 Bar. I tested over and over again on all gears, reaching 6.5k + rpm. Hose recently changed and leak test done. Funny thing is, before I change the hose, the car can sometimes boost up and the power did feel like a 300hp car so I think the peak boost was higher and that the turbo was functioning well. What can be the problem ?

1. ECU/chip fried ?
2. pressure sensor in ECU not working ?
3. I also heard that there is a vacuum pipe leading to the ECU pressure sensor that can generate a huge loss in power (60hp+). Anyone has photos ? I can't find anything on the VAG parts diagrams.

Question - Vacuum Pipe to ECU
When re-piping the vac pipes to Ecu the other day, i found what looks like a small fuel filter without the paper element inside, obviously a vacuum accumulator, is this actually needed???? can it be done away with and piped staright through to Ecu??? or will this cause problems???

Answer by UrS4Boy
Water trap, moisture trap, whatever. Its part of the boost/vacuum hose system between the intake manifold and the manifold air pressure (MAP) sensor in the ECU. Its there to protect the ECU from damage. Don't eliminate it. Make sure the hose clamps on it are on tight. Its a famous way of losing 60 hp on an AAN C4 S4 (fire wall mounted). The OE hose clamps get weak and the boost hose comes off the moisture trap and you only get wastegate spring boost levels. (BTDT - once)

[david]

i think you've got a boost leak.
check all hoses and including intercooler.
do you have a mark H mod on ic?

[UrS4boy]

You definitely shouldn't eliminate the moisture trap (fuel condenser), it is there for a reason. Links to more info about the Manifold Absolute Pressure (MAP) sensor inside the ECU, the Wastegate Frequency Valve (N75 WGFV), the fuel pressure regulator, etc, can be found by following the link below and then clicking on the labels in that diagram. (Note: The diagram below is static and is just there for information purposes about what some of the vaccum lines coming off the ADU intake manifold are for).

http://members.shaw.ca/speedtek/UrS%20Engine%20Bay%20Device%20Map.html

[hermanio]

is there any slack in the trottle cable ? is the trottle fully opening ?

[prj]

When you leak tested it, how long did 0.5 bar stay in the system?

Also, pull fault codes.
If there was anything wrong with the ECU, your car would not start, so forget that for now. For MAP sensor in ECU you would get a fault code - but these almost never fail.
Have seen 1 failed after working on 150+ of these cars.

But yeah, check your codes instead of guessing.

[wowow]

YOu guys are most helpful !

Questions :
1. assuming ECU and pressure sensor is fine ( as no fault code came up ), how to check if the Moisture trap is ok ? Should I just replace it anyway ? Any idea where to find one as I have tried ebay and googled it. Found one but it looks nothing like the one in the diagram UrS4boy showed. I also found another diagram explaining the Moisture trap, but it shows that there are 2 traps.... confusing
2. "do you have a mark H mod on ic?" do you mean mod on the chip ? no, I believe its original. But the last owner have certain messed around with it. Any knows how I get get a chip with the original program ? I found a whole bunch of source codes but I am not sure if there are indeed the right files. Dropbox link : https://www.dropbox.com/sh/evi6qmq77fswqtp/6DF9z226FA
3. "is there any slack in the trottle cable ? is the trottle fully opening ?" If the car can go up to 7k rpm, then I guess the throttle must be functioning I guess. Is my assumption correct ? Or the car can still go up in rpm with throttle not fully opened ?

[UrS4boy]

YOu guys are most helpful !
Questions :
1. assuming ECU and pressure sensor is fine ( as no fault code came up ), how to check if the Moisture trap is ok ? Should I just replace it anyway ? Any idea where to find one as I have tried ebay and googled it. Found one but it looks nothing like the one in the diagram UrS4boy showed. I also found another diagram explaining the Moisture trap, but it shows that there are 2 traps.... confusing

The schematic diagram with the integrated photos and labels shows two moisture traps just to show that there are two different types not that there *are* two traps. As long as your moisture trap is not split and can handle 2 Bar of pressure and the hoses from in the intake manifold to the ECU are attached firmly (with clamps) to the two nipples on the moisture trap, then you are fine and you need to look elsewhere for the solution to your problem. You seem to have the same type as the UrS6 got.

http://forums.quattroworld.com/s4s6/msgs/140113.phtml

The Mark C. mod relates to the method of attaching boost hoses to the RS2 (and S2) intercoolers (others will correct me if I am wrong).

[wowow]

I can see the moisture trap in my engine bay

[prj]

If the problem was the moisture trap you'd have a code.

Has the dump valve been replaced? Are you running the standard item?
Also, you still have not said how long it holds the 0.5 bar pressure. You just say "leak test done"....

[simon20vq]

Are the pipe on the n75 connected the correct way around or split?

[wowow]

May I know how "around" and "Split"is done ? I did it the same way as diagram I showed earlier.

[Bosscat]

boost

I know its a bit far out but took me ages to locate it - duff MTF - dropping the boost to in my case 6.5 on the normal S2 ????

[UrS4boy]

I can see the moisture trap in my engine bay

Sorry, I can't see it. Give us a hint. I see a bunch of things, ISV, Fuel pressure regulator, intake air sensor, dash pot, etc. but no moisture trap/fuel condenser.

[UrS4boy]

If the problem was the moisture trap you'd have a code.

Disagree. Not in my experience with an AAN. Hose comes off the moisture trap, there are no zero nada kein codes, just a loss of power.

What code do you think gets thrown?

[mcandmar]

Moisture trap is behind the left hand side kick panel, i.e. remove the side pillar trim below the glovebox. I doubt it is that, any leak around there you will hear. You are right in that the hose can pop off, has done so on our S4 a few times. The S2 has a different unit that never gives any issues in my experience.

As Prj has asked, does the system hold pressure? With the crank case breather and wastegate lines plugged up, and testing from the MAF connection to link pipe connection it should hold pressure for a long time, as in have a cup of tea and it should still be holding 1bar. Testing with the intake manifold connected wont hold the same pressure, anything above .5bar you get cyl blow bye and start to pressurize the crank case. Mine spits the dip stick out at about .8bar