> Do you know if this happens at

> a given throttle position (for example when the throttle position

> sensor registers more than 3/4 throttle) or is it another factor?

The ECU senses WOT using the throttle position sensor.

Backing off the boost in the case of the S40 turbo's was explained to me by some tuners as being a system of 'credits' in the ECU code. Because it's running rich will the cat converter start to heat up above it's normal temperature (too much partially burned fuel input to convert). This temp-increase in time can be calculated and put into a table.

Every time-period this situation happens the ECU detreacts one 'credit' from the heat-budget of the cat-converter and once the budget is gone it will need to take action or the cat converter could get damaged (eg. ceramic core damage)

The way it does this is by lowering the boost and leaning out the mixture again. The cat converter cools down again and after a while it will allow more pressure again, but usually only after the 'user' gets off WOT for a moment.

The reason for this is simple.. Volvo, as a car manufacturer, has to make sure that everything stays working properly and save money everywhere. A sticker/tag saying "do not use WOT for more than 20 seconds or the cat may be damaged" simply doesn't work, so safeguards like this are built into the ECU code for 'joe public'.

But even on the german autobahn going to WOT is a relatively rare situation.. 'cruising' at around 140mph in a T4 doesn't require full throttle either, but can be sustained indefinitely (traffic and fuel permitting :) Did that a few times (Munich to Kiel in a day to catch the ferry to Gothenburg) and the car didn't even break a sweat or run hotter than normal. Tires did get nice and toasty though and really stuck like glue :)

If someone added a different downpipe, exhaust and perhaps a race-cat that can handle higher temperatures then an adapted program could probably be created without these features but it would be 'at your own risk'..

Of course the way 'around' this is to keep it just off WOT. The 'safeguard' system won't be needed and the boost will stay up until the intercooler can't cool the air enough to prevent pinging/detonation under high boost (it slowly starts to heat up itself and output air temperature slowly rises). Once the ECU detects pinging (or actually the precursors) it will start the same sort of protection mechanism as at WOT: enrich the mixture, retard timing and lower boost.

BTW.. On the LPT engine it probably never even has to do this as the air temperature coming from the turbo should stay relatively cool by itself (would be interesting to measure and see if the IC is really needed in these cars anyway)

Bye, Arno.