Hi everybody,
I have Magna TW 2005, 106k kms and i have problem with fuel consumption:

1. The fuel/100kms indicator on dashboard usually show about 22-25 lits/100kms. I drive around Marrickville area in Sydney, rarely at nightime or use air conditioner. I can only do more than 300kms with nearly full tank, about $60.

2. I buy the car 2 months ago and it only use around 13-15l/100kms (city area)

3. Other (maybe related) symptoms:
- Delay accelerating at low rpm, especially when from stop.
- I feel engine vibration for a while when i push the gas pedal at low speed. After that, it disappeared.
- It's not smooth when gear changed, i see the rpm decreased suddenly while i keep pushing gas pedal (when it reach about 2500rpm, it go down to around 1700rpm and after that go up to over 2500).

What happen with my car? I recently change timing belt, transmission fluid, engine mount on driver side, drive belt. I read some thread on the forum that fuel consumption problem due to O2 sensor but Im not sure it's my case.

Thank everybody.

The dash display of fuel consumption has a weakness in that it doesn't compensate for the fuel flow through the injectors at idle, where the ECU has to use longer injector pulses to compensate for injector opening latency. The dash display just monitors the injector pulses, and when the engine spends a lot of time idling it will grossly miscompute the amount of fuel used (it will indicate much more has been used that has actually been used).

Also, Magnas seem prone to showing empty on the gauge with still a fair bit of fuel in the tank (even the reserve comes on with lots left - typically more than 10l).

I don't know exactly how much you are paying for fuel (or what type of fuel you're buying - E10 will result in about 4% worse economy than 91RON ULP), but as near as I can make out for $60 you would be getting around 45l, which for 300km gives just around 15l/100km. While this is a bit on the heavy side, it isn't wildly so (from what I've seen, 11-12l/100km is not uncommon in city driving in a FWD 3.5l auto Magna). I would suggest carefully correlating the distance you travel with actual fuel consumption (fuel purchased) before worrying too much about this.

With regard to your odd engine response, I suggest checking the condition of the Idle Speed Controller (ISC) first - a good clean may be in order. I would then suggest having the ignition coil in the distributor checked, particularly if the problems appear worse in hotter conditions than cooler conditions and then other ignition system components.

The oxygen sensor could be contributing to poor fuel consumption - the simplest way to test this is to disconnect the sensor, temporarily disconnect the battery (which resets stuff in the ECU) and then see whether the engine runs better with the oxygen sensor disconnected. If it does, replacing the oxygen sensor should be considered. 3rd gen Magna ECUs will not show a CEL for a faulty oxygen sensor.

The dash display of fuel consumption has a weakness in that it doesn't compensate for the fuel flow through the injectors at idle, where the ECU has to use longer injector pulses to compensate for injector opening latency. The dash display just monitors the injector pulses, and when the engine spends a lot of time idling it will grossly miscompute the amount of fuel used (it will indicate much more has been used that has actually been used).

Also, Magnas seem prone to showing empty on the gauge with still a fair bit of fuel in the tank (even the reserve comes on with lots left - typically more than 10l).

I don't know exactly how much you are paying for fuel (or what type of fuel you're buying - E10 will result in about 4% worse economy than 91RON ULP), but as near as I can make out for $60 you would be getting around 45l, which for 300km gives just around 15l/100km. While this is a bit on the heavy side, it isn't wildly so (from what I've seen, 11-12l/100km is not uncommon in city driving in a FWD 3.5l auto Magna). I would suggest carefully correlating the distance you travel with actual fuel consumption (fuel purchased) before worrying too much about this.

With regard to your odd engine response, I suggest checking the condition of the Idle Speed Controller (ISC) first - a good clean may be in order. I would then suggest having the ignition coil in the distributor checked, particularly if the problems appear worse in hotter conditions than cooler conditions and then other ignition system components.

The oxygen sensor could be contributing to poor fuel consumption - the simplest way to test this is to disconnect the sensor, temporarily disconnect the battery (which resets stuff in the ECU) and then see whether the engine runs better with the oxygen sensor disconnected. If it does, replacing the oxygen sensor should be considered. 3rd gen Magna ECUs will not show a CEL for a faulty oxygen sensor.

Thank you mate.