[SimonB]

What would cause increased fuel consumption (other then an increased desire to get places faster)

Last year, on the open road with roofrack, I averaged about 7.5-8km/l. In traffic it was about 6.5.

This year, I am lucky to get 7km/l on the open road (doing a gentle 105-110), and less than 6 in traffic.

Now my idle control valve is buggered, but they just circumvented that by setting the idle speed higher until I can find a replacement ICV. Only other difference is new takkies but the fuel consumption started increasing before that.

[4ePikanini]

welcome to my world.

I'm trying to figure it out as well.

[4ePajero]

Petrol engines use more fuel for one of these reasons (some will cause small differences, others major ones):

• higher speeds
• more aggressive driving style
• less efficient fuel system, which can be because of one of the following:
  • fuel system faults, such as to rich a mixture
  • injector failure
  • blocked air filter(s)
  • rubbish petrol (try another brand)
• electrical / electronic problems:
  • spark plugs (gap/type)
  • HT leads (spark plug wires)
  • coils / coil packs
  • ECU malfunction
  • ignition timing (setting / advance)
• mechanical problems:
  • loss of compression (rings / valves)
  • valve timing (slipped a tooth on belt)
  • worn cam lobes
  • valve clearance
  • PCV (positive crank case ventilation) influencing mixture
  • leaking vacuum hoses (eg to brake booster)
  • carbon build-up
  • exhaust system blockage / damage
  • dragging alternator/AC pump/power steering/water pump due to bearings or miss-aligned pulleys
  • incorrect engine temperature
  • slipping clutch (you should notice that, though!)
• Other:
  • tyre pressure
  • binding brakes
  • wheel bearings
  • wheel alignment (should show in wear patterns)
  • aerodynamic changes (roof racks, lifts, belly-plates/whinches, bull bars, spots, mud flaps, etc)

To tie it down is often a problem. The least you can do is check for the obvious.
Usaully the fault is to rich a mixture (major culprit).

[SimonB]

Thanks... car is due for it's 200k service so will ask the mech to do a thorough check...

The one thing I have noticed is that when pulling off under labour (like when in the wrong gear) she seems to hesitate, and then go again (my instinct says misfire but my instinct is usually suspect)... could that point to something?

[RoelfleRoux]

Simon,

These electronically controlled engines are strange creatures. A "buggered Idle control valve" will in all likelyhood affect some of the other parameters. What do they adjust when they up the idle speed? Logic suggests that you first fix what is known to be buggered, then take 4e's list and first eliminate what you think is not the cause. After that, good luck!

What about something really stupid like a shift in the accuracy of your odometer/speedometer?

Any ride height changes made?

[Scubadude]

Apart from the well known fact that fuel economy is inversely proportional to the weigth of the right foot, I'd check out plugs, coils and HT leads.

Oh yes ... the new tyres may add an illusion of higher fuel consumption (larger rolling radius, fewer truns per km, fewer recorded km's for fuel used).

[Theunsb]

Ja Boet. Bigger tyres and now you mention it. Eina.

[SimonB]

The tyres are the same size as my old ones... and the consumption increase started when I still had BFG's... so I'm confident I can discount the tyres