Open exhaust causing overboost?

[fattyjr]

Morning, I've just completed removal of the downpipe cat and dpf off my v9x. Where the dpf unit was In the exhaust, I've installed a exhaust valve which bypasses the mufflers. It's currently wide open as I've got to do the electrics for the valve.

Vehicle sounds great, drives brilliant, but I've noticed that it seems to stop revving at 3000 rpm occasionally. I think it might it might be overboosting, but it's not setting the eml on the dash. Turn off the key, leave it 5 mins and start it up again, everything ok. Any ideas?

 

[Old.Tony]

The tightest restriction in the exhaust system is the input to the turbocharger. Everything after the turbine is less restrictive (unless it's blocked, but as it's beyond the turbo, the effect on the turbo will be minimal).

If you're overboosting (you can check, the ECU monitors this: either a workshop tool (Snap-On, others) or a Bluetooth ELM327 OBD2 adapter and an OBD app on your phone (eg Torque for Android) and you can monitor the boost levels to see if that's happening.

This lack of revs without any engine light and fixing it by restarting is actually common on the YD25 engine when the SCV (a replaceable part of the fuel pump) starts do degrade. It might just be dirty (injector cleaner does work if that's all it is) or it could have some damage (usually some scoring) and replacing it is really simple. If your turbo is boosting properly, chances are it's your SCV and some injector cleaner would be my first recommendation.

 

[fattyjr]

I actually had a code pop up which is p2031 for a exhaust gas temp sensor which was supposed to be mapped out.

 

[tweak'e]

they may not have gotten rid of the ecu checking the sensor is actually there. i don't have the book for that model, but see what the code relates to, sensor temp or sensor wiring.

 

[fattyjr]

It's a werid fault as on the way to work this morning, it was driving fine for 5 mins, then pulled out of a junction and it was like someone put a brick under the throttle. Got to work and checked for codes and nothing.