eduardo

I'm trying to understand the effects of chipping a 2.7T and would appreciate any and all
answers to the following:

1. How are the turbos controlled by the ECU? I understand that each turbo has a wastegate that
opens when the intake manifold presure exceeds certain value. Is there also a recirculation
valve than feeds intake presure into the exhaust manifold to keep the turbos spooling when the
throttle is released? Or did I get the plumbing wrong? What does the ECU do?

2. How do things change in a chipped car? I read that the ECU sometimes "fights back" and
"learns" to reduce boost and you have to disconnect the battery so it will forget. Why is this? Is
it unavoidable or the result of imperfect chip parameters. Does it also happen with stock chips?
Is there a way of knowing it is happening other than "feeling" the loss of torque?

3. Here and in other forums I have seen two entirely opposite opinions expressed as to the
ability of the dealer to know whether a car is chipped or not. APR and, I beleive, Garret too say
"the dealer cannot detect the chip unless they open the ECU or drive the car". Some people
working at dealerships say "we know the car is chipped the minute we plug the computer".
Who's right?

Again, thank you for any comments.

Pete S4

1) Yes the ECU controls the boost pressure in the S4. There's no recirculation valve that dumps intake pressure into the exhaust. The ARE separate bypasses around the both the exhaust and intake sides of the turbo.

2) I really doubt this happens.

3) Lets just say the truth is probably somewhere in the middle. Both sides have reasons to make you think one way or the other. Personally I think the only way the dealer will notice is if he finds error codes (normally doesn't happen), notices the car has more power than usual, or actually opens up the ECU. If you are very worried about this, get a second ECU like a number of us have.

Peter
'00 S4
APR Stage 1/Tip

Bichon

1. My understanding of the system is as follows: The boost pressure is controlled by the wastegate. It is a mechanical valve that opens and routes exhaust gases around rather than through the turbo. The valve is set to open at around 5 psi of intake manifold pressure. Inline between the intake manifold and the wastegate is the wastegate frequency valve. When the frequency valve is energized, it disconnects the wastegate control from the intake manifold and lets it see atmospheric pressure. By rapidly switching back and forth between manifold and atmospheric pressure, the ECU allows boost to rise above 5 psi. The percentage of time that the wastegate is connected to the intake manifold vs. the amount of time it is connected to atmospheric pressure is called the duty cycle. The duty cycle required to produce a specific boost pressure is stored in a table in the ECU, and is fine tuned with a feedback loop using the pressure sensor atop the throttle body boot.

2. In a chipped car, the tuner changes many of the values stored in ECU tables, changing boost pressures, timing and fuel maps. The "ECU fighting back" that you talk about has nothing to do with reducing boost. The ECU has knock sensors that detect pinging and will retard timing as soon as it is detected. Initially, it will use the timing values programmed into the chip, but if it needs to make corrections frequently due to knock, it will apply a set of corrections to the values programmed in, resulting in more retarded timing values being used at all times. Pulling the battery cable erases those corrections, so the ECU will start using the values in the chip again. Most people on this board feel that the timing adaptation is the result of using lower octane fuel than required. A recent report on 20/20 told of a widespread problem of gasoline stations cheating the public by selling lower octane fuel than marked on the pump.

3. Most chips don't announce themselves on the identification screen, and I am not aware of an easy way of telling just by connecting a VAG tool while parked in a service bay. If the dealer has reason to suspect you are chipped, he can watch the "boost target" data block on the VAG as he accelerates, and immediately see values above the 1700 mbar max he would see with the stock chip.

Just a stock S4

So the wastegate works just like the injectors, huh? Thanks.