Aggressive Fuel Cut or Similar?
 

Hi,

I have a query about my car (WRX PPP 'blobeye'). Occasionally when changing gear or sometimes just suddenly coming off the throttle (I guess both of these are similar but its totally random) when on full boost the car seems to 'really' come off boost. It's hard to describe - it's like the engine hitting its mounts, or fuel suddenly being cut or maybe a sticking DV or something? No funny noises or bangs etc, just like power has been cut very quickly - you can feel the 'stutter'. No issue when back on the throttle though.

Anyone know what might be causing this - the car has just over 20k miles, Tesco 99 in the tank. It does not happen all the time - can go days without doing it.

Thanks in advance.

Sounds like you have already said what the problem is:

You are hitting fuel cut on WOT... what is your car boosting too? Probably over boosting which is why its hitting fuel cut

The most I've ever seen on the Lamco boost gauge was around 1.25bar peak (certainly no more). What is the max boost allowed before cut? Car is totally standard.

agree with above probably overboosting slightly is the car still std ppp spec or have you changed anything.

As far as I am aware it's totally standard PPP - no reason to believe otherwise. Since I got it and started using Tesco 99, followed by an ECU reset a few tanks later, I think the peak boost has raised slightly (previously didn't go over 1.2bar) and the car feels much smoother, apart from the issue I'm having.

I think it's only 'just' hitting it hence it does not happen often. You do definitely feel it though when it does - just strange it is when coming off the throttle? Maybe it's just something you learn to live with?

You may find it might be due to the cold temperature, air denser, which means it could boost a bit higher then it did in the summer, which is why it might be hitting fuel cut.

Check vac pipes for splits, that can cause over boost.

Just thought I would bump this in the hope someone may know the issue as it still seems to be occurring...

It is NOT happening on full throttle (WOT) - it is when you come straight off the throttle from full throttle (to slow or change gear), but the car is over 3000rpm (under peak boost). So it seems to be at the time when the car would usually be dumping boost on gearchange.

I've tried some Googleing but haven't had much success. The car still pulls fine straight after the next gear is engaged too.

I realise some people say the car is overboosting but would have thought if that was the case the car would cut under hard acceleration - not when coming off the throttle?

Any help appreciated.