I was joining the motorway last night and gave it some beans WOT but at approx 6k RPM in 4th gear the car made a horrendous jolt like I had hit a brick wall, it took me totally by surprise.

I immediately came off the throttle but the car continued to drive normal and no CEL light came on. I did not push it hard after it happened.

Car is a 2008 UK STI Hatch with a Turbo back decat and Induction Kit. The car is remapped.

Any ideas what could be causing this?

Id considered the following and will be checking the car over at the weekend:

Boost Leak?
Vacuum Leak?
Dirty MAF?
MAP Sensor fault?
Fuel Pump fault?
Bad Spark Plugs?
O2 sensor fault?

 

Incomplete map

 

How much fuel did you have in the car?

 

Low fuel ?
Upgraded fuel pump with small sock ?

 

I did have low fuel, approx 1/4 of a tank and I think it is the original pump.

Am I right in thinking the 2008 onwards hatches do not have fuel filters, they are an integral part of the tank fuel pump?

 

Possibly a combination of the pump and low fuel, for £75 I'd chuck another pump in

 

Overboost protection, has an em problem

 

+1 for the above or a pipe has come off near your boost solenoid area have you had a 3port put on? I had one for this and it was a crack in the vacuum pipe they get do get brittle and one time a pipe was left off the 3port and driving home it did exactly what you describe.
You do have a fuel filter situated were the pump is yes on the tank most dealerships will tell you they don't even know if there is one!!! I replaced my mates on his hatch alittle while ago as it had been in over 60k miles and it is a replaceable filter no need to change the pump

 

Fixed

(I think lol)

The charge air hose on the back of the intercooler (the 90 degree one that goes between the Y pipe and the turbo) had a small split. The jubilee clip was not aligned properly, it was crossing over the edge of the hose onto the metal Y pipe, cutting into the hose. The teeth on the clip had chewed away the silicone and was flaking off, where it had been tightened a small split had started.

So Im guessing a boost leak caused this? Or the boost leak meant the air/fuel ratio was out?

I got a Samco kit and changed all the charge air hoses and new clips. Taken her out for a few blasts now with WOT and - fingers crossed - no more horrendous jolt!

 

Nicely executed now werz the pic of theses samco hoses in the engine bay