UnSubRocky wrote on Sep 29
th, 2026 at 10:23pm:
I changed my front tyres and had a wheel alignment on my car. The fuel efficiency must have improved 25%, and my speedometer matches my actual speed.
The other day, I put in some of the petrol injection cleaner. Then I filled up the car with $80 worth (from 1/8th full to full) $2.40/L. The car had been running somewhat rough. Being not mechanically-minded, I just thought that it might be worth a go to get the vehicle running smoothly in a few days time. The car started up nicely and ran with a bit more power (although only slightly better). I was under the impression that the injector clean takes a few hours at least to improve performance.
Wheel alignment isn't going to make any difference with economy if car wasn't pulling hard to left or right.
If car was pulling left or right perhaps something is worn or bent in suspension from kerbs or potholes.
Australian Design Rules for speedo says speedo must read higher than actual speed so when doing 100kph indicated it might only be actual 93-98 Kph.
The new tyres probably have slightly larger diameter due to not being worn out which probably accounts for difference if using GPS to calculate speed.
Injector cleaner is a waste of money better off keeping fuel filter replacements up to service intervals.
Fuel filter is more likely to clog up reducing fuel flow than injectors getting clogged up in which case injector cleaner isn't doing anything to fix that.
To properly clean injectors they must be removed from car placed in a machine that squirts fuel down injectors then individually records fuel flow from each injector into a tube.
It's common for new injectors same type to have flow difference of 1-3%.
Modern cars have O2 sensor in exhaust they run in closed loop where it continually gives feedback to ECU if injector is slightly clogged (very rare) then ECU will notice car is running slightly lean and increase pulse width to injector to squirt more fuel.
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