Hi guys, my Verada has just gone for a tune up service and now that it's been a few weeks from it, I'm starting to notice a few problems with the car. I don't know if it's just me but I've noticed that fuel economy has been dropping and it seems to lose power when going up a hill on 1st and 2nd gear. It will do this randomly and is not consistent with how I'm used to driving it.

The issue of fuel economy is bothering me as I had always gotten high 200 kms out of a full tank of Vortex 98 at my local Woolies petrol station. It's now dropped to roughly 150 at most. My route has remained the same largely, being suburban travelling in the inner west of Sydney.

Occasionally it will take a lot of power to accelerate and when I force it the car makes a loud vibration and a rumble. Opening the windows allows me to hear what sounds like a muffler leakage. This happens at random, and I cannot seem to pinpoint what issue is causing it.

The things done in the tuneup were consistent with what you'd normally have done – oil changes etc. The only other thing done after that was a muffler gasket changed (are these compatible with other car models?) and also the spark sensor.

I have no idea whether these things were actually done or not, but I'm very worried I may be hurting the car by leaving it as is.

Your help is really appreciated here

The issue of fuel economy is bothering me as I had always gotten high 200 kms out of a full tank of Vortex 98

WTF - What The Fuel..... 200Kms - I'm severely annoyed at 500Km or less out of Ron 95 fuel... Your catalytic converter and/or oxygen sensor is stuffed, or is your calendar stuck on april 1st? 200Km Really? I get better than that out of my Jaguar V12 - well just...

WTF - What The Fuel..... 200Kms - I'm severely annoyed at 500Km or less out of Ron 95 fuel... Your catalytic converter and/or oxygen sensor is stuffed, or is your calendar stuck on april 1st? 200Km Really? I get better than that out of my Jaguar V12 - well just...

Agree, that was what I was thinking. I do a severe slow crawl through traffic every day and my car still gets high 300's out of a tank of 91. In the first instance I would take it back to where you got your 'tune up' and let them check it out.

I have no idea whether these things were actually done or not
This statement concerns me more than the fuel economy

I only don't know as I wasn't there to pick up the car, the mechanic is known to my parents.

Even before I bought it and the tuneup, the car would go smoothly. At one time I only got 48km out of a full tank of 91 e10 so I assumed 200-300 per tank of 98 was normal. How in the world do you guys get 500km+?! Is the catalytic converter an expensive repair? ;_;

48km out of a tank of e10......... comon is this a troll post?

reg 91 mine gets 400-450 with mostly stop and go "city" driving and tbh the engine is not in the best shape from previous owner and my being unable to do work myself due to injury

Something's very wrong, 450km from a tank (that's in a wagon whose tank is a bit smaller than the sedan) would be around the worst economy I get, ie. city driving. 600+ is common on highway. Your economy is so bad I'd suspect a non-functioning MAF, but that should throw an error code. Either that or there's a hole in your fuel tank!

I legitimately cannot believe how bad my fuel is in comparison. There's no error codes so I'm not convinced it's the MAF, but I do have a feeling it's the cat converter because of the ground rumble I feel. It's done a long way, almost 289000 kms all up.
I'll check the cat and see what I get. Right now I've done about 150km and that was half a tank of Vortex 95.

As bb61266 said O2 sensors are a common wear-and-tear item that can lead to poor fuel consumption. I'm not sure if replacing the sensor alone would bring you to an acceptable fuel consumption level nor fix the rumble, but if they're still original, I'd be replacing them.

48 litres from a tank equates to 147 l/100km... that's more than a dodgy oxy sensor! By your latest figures, assuming it's an accurate 150km at half a tank, that comes to around 24 l/100km, when for mixed city/country you should be getting something below probably 13 at worst (there's a bunch of threads on fuel economy, I don't want to start another one here). Impossible to diagnose online if you're not getting any error codes, but I'd definitely get it looked at.

Bad fuel economy can also be the result of a loss of power or an increase in rolling resistance, which is compensated for by flooring it.

I've just bought a new air filter as I think this one was in there since new. I looked at it and it's grey as pencil sharpening. If this still leads to the power loss and bad fuel, I'll get another O2 sensor. Hopefully I won't have to bring it in for a cat converter because I am running poor with repairs ;_;

I've just done a full tank of 95 Vortex and the figures seem consistent with pre-tune up, which was 320 km per tank. Regardless, it seems it could be a lot better and I've only barely seen the 300 figure on my odo

Still bet O2 sensor, my TS magna had the sensor fail all of a sudden one day (ie: total failure not partial like you) - I drove 300m+ down hill about 40Km and used 1/2 a tank of fuel - lucky our next door factory was an auto electrician because the bonus was not only did he diagnose it, the factory sensor at the time was like $700, he put a generic one in vastly cheaper - and it was still going strong 3+ years later when I sold the car.