Reduced fuel economy

Dras · Post by **Dras** » Wed Jun 24, 2009 9:58 am

Hey guys,

My car has just recently hit 160,000 Km and I have just recently noticed a big increase in fuel consumption, literally from one tank to the next. I consistently use Shell Optimax from the same servo and have gone from a very consistent 11L / 100km for years to now to 13L / 100km.

After I noticed the drop I have had the car serviced and all the oils / filters (including the fuel filter) have been changed.

At the same time that I noticed the reduced fuel economy, I also noticed the voltage at idle to be lower than what I think it should be. At idle the voltage is around 12V with the A/C and headlights on. (I am not sure if this is at all related.)

The car does not appear to be leaking fuel from anywhere so my first guess would be the O2 sensor. What do you guys think?

Post by **I8A4RE** » Wed Jun 24, 2009 12:00 pm

02 sensor bro, check out my guide in the DIY section more info

Post by **aza013** » Wed Jun 24, 2009 5:32 pm

2nd the O2 sensor.

nikhan · Post by **nikhan** » Wed Jun 24, 2009 11:52 pm

and u might wanna check your cat convertor too

Dras · Post by **Dras** » Wed Jul 22, 2009 9:37 am

I have replaced the O2 sensor for a generic Repco sensor, reset the ECU and given it a 3 tanks of gas for everything to settle and I am still getting crappy fuel economy.

At 160,000km could it really be time to replace the cat?

Post by **Bennoz** » Wed Jul 22, 2009 10:24 am

Sure could. Give it a rattle, you hear anything moving, it'll be shot.

Post by **vipfto** » Wed Jul 22, 2009 10:28 am

doubt cat, look at plugs and filters check error codes

Dras · Post by **Dras** » Wed Jul 22, 2009 1:39 pm

The car has new filters and spark plugs all round.

Post by **I8A4RE** » Wed Jul 22, 2009 3:03 pm

Yup could definitly be the cat......or a fuel leak.

I did a service on the misses boses car a 3 months ago and he was complaining of a fuel smell lately.

I asked him "since when" to which he replied "umm probably since the last service" (which was done by a workshop

). So I carried out service then started to investigate fuel smell, took me about 30 seconds to find. The screw on the lower fuel line into the bottom of the fuel filter was completely undone.

He came back to me a couple of weeks later saying the car has never run so better and fuel economy has imporved 3 fold (I was thinking yeah it helps when the engine actually gets the fuel instead of leaving it on his driveway)

Dras · Post by **Dras** » Wed Jul 22, 2009 3:22 pm

Other than taking the CAT off and shaking it to see if it rattles, is there any way to test the CAT?

While I don't think it is the case but my voltage at idle is around 12V with the A/C on, could this be producing a too weak spark?

koolio1234 · Post by **koolio1234** » Thu Jul 23, 2009 2:30 am

Dras wrote:While I don't think it is the case but my voltage at idle is around 12V with the A/C on, could this be producing a too weak spark?

Highly doubt it.

Im getting some pretty bad economy myself @ 132,000km. I'll probably be doing my 02 sensor and look at changing the the cat.