[zooker]

About a week ago I noticed a small exhaust leak coming from the join between the exhaust manifold and the pipe (before o2 sensor, running G16B fuel injection).

Then yesterday while driving home I was driving up a hill and there was a sudden change in exhaust noise (got louder and sounded more like it was coming from engine bay) and there was a noticable drop in power. Up a hill it usually cruises up, it just bogged down and I had to drop back a gear and floor it to make it up. I pulled over and checked the manifold because I knew of the small leak, and its now a big leak (can feel exhaust blowing out when engine revs).

My questions are, can an exhaust leak from near the manifold cause such a drop in power?

Would this possibly be because the leak is before the o2 sensor, so the ecu isnt getting the right reading and so running the engine rich/lean?

Would the leak have been caused by a blocked cat/muffler, which would then explain the loss of power? The cat is not even 6-months old so I hope this is not the case

I plan to pull the manifold and exhaust off and replace the gaskets to try to stop the leak, and hopefully get the power back if this is the cause.

[Scrawny]

Yes, fix the leak and re-check. I think you'll find you are dead on the money, excess air upsetting the o2 sensor. If it's not the problem, you had to fix it anyway. More than likely not the cat.

[Damo]

I have a little exhaust leak to fix too, dang it.

[magnat]

I think I have several...
one would be the internal baffling on my muffler is stuffed and I think I bottomed out on the front end and bent the exhaust somewhere near the collector..

[Hybrid]

Your spot on. I read about of a lot of these problems when custom fitting efi to carb engines. Basically when you have a leak before the 02 sensor it doesn't show up at all times rpm points/engine loads. Most of the time the pressure from the exhaust gasses flowing stop the air entering and it runs fine. Under certain conditions though it draws air in. The o2 sensor reads lean when its not so the ECU bumps up the mixture. Now the engine is running rich but the o2 is still showing lean so it pumps even more fuel in. The mixture ends up super rich and the car will run like shit if at all. Next minute the conditions change (rpm/load) the exhaust gas pressure stops any air entering and the car goes back to running normal. I've heard it leads to a lot of heart ache when custom tuning because a small exhaust leak is generally missed in the diagnosis and the 02 sensors reading is taken for gospel.

[zooker]

Well replaced the gasket today, so one problem fixed.

I noticed a bit of a rattle coming from the exhaust in the last couple of days, figured it was something loose. Anyway, while I was under fixing the gasket I bumped the cat and it rattled Sounds like somethings come loose and rattling round inside, which might have blocked the exhaust flow, leading to the drop in power I experienced. And when I started it up I saw tiny flakes of a ceramic like substance coming out the exhaust So I think its farked

I had a look round on the net on busted cats, because this ones only 6 months old and should last longer than that, and found that they can break down due to the engine running too rich, excess fuel burning up in the cat and destroying it.

Soo I think the engine has been running rich due to exhaust leak near o2 sensor, and/or damaged o2 sensor, leading to the farked cat. Not happy

So its off to the exhaust shop for me, will have to replace cat, will get a new o2 sensor just in-case, and try not to let the engine run rich again.