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A question related to Car average mpg display correctness I suppose, but say if a piggy back chip (e.g. http://www.dieselandpetroltuning.co.uk/) was added to a diesel car with trip computer, would the trip computer take into account the extra fuel injected via the remap/chip, or would the increase in fuel consumption be ignored and make the trip computer less accurate?

Sites selling chips such as these claim

Improved MPG for high mileage drivers

but to test these claims, would you have to measure the relative consumption manually rather than use the relative values reported by the trip computer before and after fitting?

Community
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SilverlightFox
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2 Answers2

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Great question. I am making an educated guess here, so don't quote me in court;)

Because piggyback chips interfere with your car's various inputs I would assume that you are correct and that your MPG score will be inaccurate as a result. I can't say by how much though. These chips usually give an MPG boost of around 10%, so I would imagine your true MPG would be 10% less than your trip computer says it is. Not that it was 100% accurate to begin with. Toyota engines have an AIr/Fuel ratio sensor that is much more accurate than the usual Oxygen sensors found in most other engines, so you're probably coming of an inaccurate base to begin with.

If it makes you feel any better, my Opel reports my fuel consumption to be 10% less than it actually is, so if I were in your shoes, it'd probably improve the accuracy;)

Captain Kenpachi
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Like @mac said, it all depends on what the piggyback/chip does. If it modifies the signal to the injectors and the ECU does not see these changes, then your MPG-o-meter will be off.

However, if it is like a "reflash" where the ECU uses new values for it's load vs RPM fuel injection tables, then it should still be as accurate.

Nick
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