fuel economy getting worse...

[perfk]

I've had my car about a month, and over the past few weeks it's fuel economy has really started to decline.

When I first got the car I was getting a steady 470-500km out of a tank.
12km/L (100km=8L)
Over the past 3 fills it has gotten steadily worse and now sits about 400 a tank.
10km/L (100km=10L)

Haven't really made changes to the engine-
Did re-route the catch can (which made it run stupidly rich) - but only had it set up that way for about 20km before we swapped it back to exactly the way it was before.

I've been running it on the same fuel since buying it (BP 98).

Am going to check tyre pressure
and intend to look up a chart so spark plugs can be checked
does anyone have other ideas as to what I can check or what might be causing this?

Car is a '96 levin if it makes any difference.

[rwd_mayhem]

you sure your right foot hasnt put on any weight?

[Mr Revhead]

using the aircon more to defog windows?
window down more?
inaccurate measurements?
dirty car with higher wind resistance?

[perfk]

-don't believe my driving style has changed
-don't use the aircon/heater (& car lives in garage, so no defrost required in the mornings)
-tend to drive with windows up all the time
-I measure fuel useage through a nice spreadsheet - taking into account unused portions, so should be getting extremely accurate readings
-shut up, my car isn't pretty enough to deserve a cleaning yet!

stupid car

[sergei]

Check your ECU codes, and VF and OX1 voltage outputs on ~2400rpm while stationary.
VF should be 1.75V - 3.75V altough ~2.5V is desirable (it has only 5 steps, 0V, 1.75V, 2.5V, 3.75V and 5V).
OX1 should fluctiate between ~0v and ~1V atleast 8 times per 10sec.

[pc]

Check wheel bearings, handbrake/brakes, tyre pressures, sparkplugs, TPS, timing... does it have a cold start injector?

Could be lots of things, but if it has just started recently and you haven't changed your habits, then that would probably mean something has failed.

[cogent]

If it helps, the car has a blacktop 20v in it. Havnt checked the plugs yet but I can do that tonight and see what colour they are.

[*84vvt*]

Whats the engine oil like ?
and when was it changed last
bet the plugs will be black