Diagnosing Poor Fuel Economy

[voney]

Righto. Everything's back together and I just took her for a bit of a drive around the city. The throttle response seems anecdotally better but I won't be ably to tell if it's made a difference until I drive it between work and home a bit.

Sjm38s: I'll have a look at the MAF again in a week and clean it again if necessary. I followed the directions on the K&N recharge but I have no idea if it was too much oil.

I mentioned the O2 sensors to a workmates that used to be a mechanic when the VT was new and he seems to thing they're only used by the engine when cruising and it disregards the signal at other times... Anyone an expert on this?

I'll try to do the fuel filter tomorrow then put some cleaner through it (or should I do the cleaner first?), I just need to grab one of those fuel line tools from repco.

 

[SJM38S]

You should be able to unclip the fuel filter with your fingers, but yes tools are easier.
The o2 sensors are indeed most important when cruising - but they are used by the ecu at all times once operating temperature is reached. (Closed loop operation is entered meaning the ecu looks at the o2 sensors, and adjusts the fuel mixture to suit, always trying to reach a preset value of oxygen level)
When you're flooring it, or when the engine is cold, the mixture is rich and isn't measured - as power or heat are desired to be increased.

 

[ephect]

o2 sensors are used to keep the fuel/air ratio optimal at all times. It's only when cold started and lean cruise (say 100kph) that they're not used.

O2 sensors would be the first thing I would be changing.

 

[voney]

Also, in relation to the O2 sensors they're the 2 wire type but I honestly have no idea if that's a good/bad thing or if they can/should/shouldn't be changed to a newer style.

And can anyone recommend a good brand, I'm a poor bastard for the next few weeks so the cheaper the better.

 

[accentstencil]

When it comes to O2 sensors you don't want to go too cheap. I bought some cheap ones once and started getting codes a few weeks later. Buy well known brands or genuine if you can find them cheaper somewhere, apart from Holden.

 

[Pollushon]

I've used the PEC brand off ebay a few times. No issues so far and cheaper than Bosch.

 

[benny_bones]

I've heard pec off eBay were terrible, go bosch they're like 90 for 2 and well worth it, won't need to replace them for ages unlike cheapies

 

[Pollushon]

I should expand: PEC is an Aussie distributor not an actual brand (they box stuff up to make it look that way, the Aldi effect). When you grab Commodore O2's off them you're either getting Bosch or Denso, depends on the planets alignment. If you go with PEC you get a quality brand name that they have a wholesale deal with. It's $20 back in your pocket.

 

[SavVYute]

A check you might do that won't cost you anything is the pcv is functioning.
While the engine is idling take the engine oil dipstick out and place a small piece of flat newspaper or tissue (2cm x 2cm) so it covers the hole.
If you pcv is functioning there will be a very slight vacuum that will just hold the paper on the end of the tube.
If it won't stay there (there's no vacuum at all) it's not working.
A stuck or gummed up pcv might be the cause of your extra dirty throttle body and roughish idle (and higher fuel consumption).

 

[NitroAl]

It's not the pcv that causes the carbon build up in the intake but it is good to know it is functioning correctly. The carbon build up is from the EGR.

You can also check for fuel leaks, a tell tale sign is the fuel gauge showing more fuel in the tank when you start the car in the morning than it did when you parked it the night before.