Hey!

I dont mind rubbish fuel economy when im driving round on the red line however when im cruising too and from work and still getting 8km/L or 17mpg im not impressed. My mates and my last Z get anything from 23-28 mpg just cruising.

Iv plugged the diagnostics in but no fault codes so what could the issue be??
Any common fault which makes them guzzel fuel?

p.s the only issue is apparently my cats are on their way out....

 

Why do you think your cats are on their way out?
How many miles do you have on your car?
How are you measuring fuel economy? In-car computer or manually?

 

A garage told me because I took it in with an exhaust rattel and they said my cats were breaking down, it explains the chalk sound the tips too.

Its a 2005 done 35k and im using the on board computer.

A manual calculation works out at an average of 20mpg to half a tank.

 

Chalk sound?

20 MPG sounds normal for city driving....but you're saying your last Z on the same route got better gas mileage? By home much and how was it measured?

Just to confirm, manual calculation:

1. Fill tank until pump stops.
2. Reset Odo.
3. Drive.
4. Fill tank until pump stops.
5. Miles/gallons = MPG (thanks for converting Km/L)

Can't do this accurately on a half tank fill up. And for this test I would even go so far as to use the same pump as they vary in sensitivity for fuel cut-off.

Cats should last way longer than 35k unless you are running really rich. Any mods on the car?

 

Sorry, I meant chalk round the tips.

Ok I will fill it up today and do the test.

I also thought it was very premature for the cats to go but when you knock them with a hammer you can hear all the crap rattling around inside and the same in my back boxes and when I removed my silencer bungs there was white chalk round them.

I though it was running rich as the mpg is poor and a few mates have said I have some black smoke out of the exhaust on full beans and the odd puff when its cold and I boot it.

Mods are, Cat back 3" system with straight through cans & K&N Typhoon

 

Are you burning oil? Do some searches on here for oil consumption...I think I remember reading that is a common issue with the 2005 MY. That would kill them early too...

 

It seems ok on the oil front to be honest, but iv been use to Honda type r's which drink oil! Im unsure weather to buy some2nd hand cats or go for a set of decats as it will prob be cheaper too

 

I thought it's only for 06