Got the O2 sensor in, plus new cat and exhaust system

The oxygen sensor is now installed, and has improved the running of the engine markedly. Shortly after installing the sensor, it occured to me that the cat converter may be worn out. I have heard that a rich mixture can cause a catalytic converter to become blocked, and since I had a faulty fuel pressure regulator, and oxygen sensor I figured it was likely that the cat converter was on it's way out. There was also a rattling noise coming from beneath the car when the engine reached operating temperature, which is also symptematic of a faulty cat converter.

When I took it to the exhaust place, (MIDAS West Ryde) they took it all apart, and it turned out that no.2 rear muffler had all it's internals loose, and the cat converter, although not blocked, only had another couple of months left in it. I had the first muffler replaced a month ago, and the weld had cracked and was leaking. I won't be going back to that place again. The guys at Midas pulled it all off and replaced it with a hi-flow cat and 2.5 inch pipes thru a single muffler. The exhaust is much more audible now on full-song. I will hold off on extractors until I have the manual transmission in it and am preparing a new worked motor.

This weekend I will be doing a bit of body work, there is a rust hole in the boot when the spare wheel sits which I will grind out and repair. The boot badges and key hole are to be removed, filled and painted. The tow bar is to be removed, and I'm shopping for a stereo.

I also have had a problem since I got the car, where is hasn't been holding coolant. The header tank would always empty after a couple of days. Just after starting it up, it would also make a noise from inside the cabin similar to water running down a wall. This seemed to come from the heating unit inside the car. The problem turned out to be an incorrect radiator cap which was leaking under pressure out the side of the cap, rather than forcing is down the return line into the header tank. A new radiator cap from Holden, and she's as good as new. The genuine cap has another rubber gromet that the dodgy one didn't have and works properly. I haven't had to refill the header tank for over a week now. It's the cheapest thing I've fixed on the car for $9.95.