mxyzptlk

need some input on this:


if one were to alter characteristics of the Charge Pressure Sender, located near the Y junction, so that it would read "lower" than actual boost pressure, one could achieve higher than stock boost. I do not have schematics or the bentley manual, but i would guess that the sender's signal to engine management is resistance. the higher the charge pressure, the higher the resistance. anyone know for sure how the pressure sender relays its info to the ECU?

since it is a closed loop system, would the ECU be able to adapt to keep mixture correct? do you think it would be so off the scale or maxed out that it would just run dangerously lean at boost?

disclaimer:
this is just a question for ones out there that have some knowledge and experience with this subject. DO NOT go out there messing with your 45K investment only to have it grenade while dynobutting it.

Tom Barber

Now there is another useful reply, ripe with detailed, meaningful information...NOT!

Tom Barber

After all, the traditional method of overriding the manufacturer's limit on boost was to modify the pressure coupling between the intake manifold and the wastegate actuator.

I am not 100% certain, but I believe that the sensors that are used to regulate boost have no impact on the rest of the engine management, i.e., fuel management. Thus, modifying it should not directly cause a bad fuel mixture. On the other hand it is possible that the stored tables that are used in the fuel management don't cover the air mass that will result. If that is the case, one of the changes that the chipped ECUs must do is expand the table. I seem to recall Brett explaining once that at low RPM/throttle, the management is "closed loop" using exhaust gas detection to regulate fuel, but at higher RPM and/or throttle, it goes into open loop, using only the stored tables regardless of what comes out the exhaust.

Why not try this and see what happens? As long as you maintain a sense of what the actual load on the engine is, it doesn't seem likely that you could do any serious damage. Also, the detonation sensor is still going to function. Seems to me this could be an easy way to save a grand or so, since the substantial gain from chipping results merely from increasing the boost limit. In order to determine if the resistance of the sensor reflects the pressure, and what the resistance is, you could first measure the nominal resistance directly (with the engine shut off and the sensor disconnected, of course). Then to measure how it changes, you would have to place an ammeter in series with the sensor. You might want to verify that the amount of current can be handled by the ammeter first, by considering the nominal resistance, and watch the ammeter very closely as the boost is increased. Even if that resistance is low, however, the current is very likely held well below a safe level by the resistance at the ECU, which I would measure with the ignition turned on.

If you have access to the VAG tool, which many people on the forum either do or will fairly soon, then it would also be useful to modify the sensor as you determine, then run it gently for a short while and check for an error code, then gradually increase, and so on. If it ultimately seems to give you the result that you want, with no error codes, and no observable impact on fuel mileage, then what could be wrong?

If you do give this a try please let me know what you find out!