Fuel Economy

[oh to dream]

hey guys bit of a noob question but hopefully you can help me out.

if the throttle is open because you've put your foot down but the rev's are still low and you're off boost do you still consume alot of fuel.

for example you're in 5th gear doing 60km/h at 1500rpm trying to save fuel, if you give it some gas to to maintain speed (so the throttle opens right up) and keep up with traffic will you consume more fuel than being in 4th gear at 2000rpm having more response and less throttle.

sorry if a few things are out of place and not explained 100% but hopefully you get what i'm trying to say and can help me out.

cheers

[paulr33]

the basis for EFI and the amount of fuel the engine uses is related directly to how much load the engine is under

the load index comes from the airflow meter, so the more you open the throttle, the more air comes in, the more the AFM shows load

so by loading the engine up in 5th gear at a low road speed, you may actually use more fuel

whereas if you were in 4th it would be less engine load to maintain that speed

the engine would rev more, but the load cell difference would be bugger all, even for a few hundred RPM increase

like at 2100rpm the load may be 5, at 2600 (cos your now in 4th) the load may be 6

the load indexes are just on a scale out of 20 - 20 being max load if that makes sense

in order to get good economy

1) pump up tyres - 40 psi is good

2) replace 02 sensor - they die after around 50,000kms, $120 part

3) reset the stock ecu

4) dont vary the throttle constantly, ie changing speed/gears, a steady throttle allows the ECU to run in closed loop mode

when the load is constant (not changing) the ECU will monitor the 02 sensor readigns and trim fuel

it does this purely for the sake of fuel economy and nothing else, ie; its not boost related etc

as soon as you vary the throttle, ramp the engine on load, bring on boost etc, it drops out of closed loop mode

and if all that fails

give the car with a full tank to your girlfriend or mother and let them drive it for a week

i bet they get good economy of out it - ie they dont load the engine up constantly and rape it flat out

[lachlanw]

drive with your boost gauge on the highest vacuum you can get .

[oh to dream]

thanks guys its making a lot more sense now. just filled up so hopefully a few changes to my driving style will get some more k's. just got 350km from the last tank with about 2l left to go.