Sounds like exhaust blowing...

Andy916 · Post by **Andy916** » Tue Jan 10, 2012 5:25 pm

Happy new year peeps.

Bit of a puzzle with the Impreza.

The last couple of weeks I've had a sound like a slight blow from the front of the exhaust. Local garage had a good look on their ramp and couldn't find anything, but commented it's possible for a wastegate crack or exhaust valve problem to give a similar noise. Garage bloke isn't a scoob specialist but does have a highly tuned old cozzie.

Apart from the slight chuffing noise it runs fine, and had a rebuild a few thousand miles ago so a valve problem seems unlikely. Exhaust midsection has a flexi bit but I don't think it's leaking. Headers are standard ported items and I don't think they usually crack. Am not sure where to look next; any ideas?

Andy

Jon · Post by **Jon** » Tue Jan 10, 2012 6:07 pm

The headers don't usually crack, but the up-pipe does (around where the heat shield is welded). I've seen it on quite a few customers cars. Also worth checking the seal between the headers and the up-pipe.
This may sound a bit rudimentary, but i've always used a short length of hose pipe (or similar) and stuck one end to my ear and moved the other end around all the joints and pipework. It's a 100% way of finding out where the leak is.

Post by **Stuart** » Tue Jan 10, 2012 7:22 pm

Top tip

IWANT1 · Post by **IWANT1** » Tue Jan 10, 2012 8:33 pm

Foot, hand or plate over the tail pipe should quickly show up the smallest of blows.

Jon · Post by **Jon** » Tue Jan 10, 2012 9:27 pm

Never been a fan of that method + it won't show up anything pre-turbo, i.e headers & up-pipe, which from experience is where most problems with power/torque loss & blowing/noise is caused.

Andy916 · Post by **Andy916** » Tue Jan 10, 2012 9:58 pm

Thanks for the help, I'll get underneath the front and check headers/up-pipe carefully. Up-pipe isn't standard, it's a 'Harvey special' to match his ported headers. One other thing we've done recently is attempt to remove the wideband lambda sensor from the downpipe, which failed but there was some heaving on it which I guess may have disturbed the joint faces onto the turbo.

cheers
Andy

IWANT1 · Post by **IWANT1** » Tue Jan 10, 2012 10:36 pm

Jon wrote:Never been a fan of that method + it won't show up anything pre-turbo, i.e headers & up-pipe, which from experience is where most problems with power/torque loss & blowing/noise is caused.

Why not, with the wastegate open pressure will build showing the blow as gases will take the easiest route?