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Old 10-15-2017, 06:41 AM   #1
sceh
 
Drives: yaris 2004
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Yaris faulty fuel consumption reading?

I have a 2005 Yaris (petrol).
Normally I average around 5-7 litres per 100kms. Suddenly I notice it is 15. When I run the car and look at the instantaneous consumption it is between 5 and 8 under acceleration but when I take my foot off and it overruns or coasts, it shoots up to 35. This is obviously distorting the average measurement.
I though fuel consumption on overrun or coasting would be close to zero.
Any ideas why this is like this?
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Old 10-15-2017, 08:18 AM   #2
Bluevitz-rs
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how long have you had this car?

can you read the fuel trims with a scanner?

Did this suddenly happen overnight?
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Old 10-15-2017, 08:23 AM   #3
IllusionX
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Does it affect real world fuel consumption?

I've noticed that mine does not show 0 when coasting.

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Old 10-15-2017, 08:30 AM   #4
sceh
 
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I have had the car for about 6 years and until recently (I would guess about 6 months ago since I rarely check) the fuel consumption average was low (5-7 litres). So, I have no idea if this happened suddenly or not but I do remember that when coasting it read low.
I have not scanned and am wary to. I had a simple scanner and it basically wrecked the engine so it would not even start. Then I bought a Tachyon which was a total waste of money because all it would do when it worked is tell me my speed (I have a speedo for that).
I suspect some sensor which is not informing the car that it is coasting though if this were the case and fuel was still being injected, it would backfire.
I could go to Toyota for an overpriced diagnostic I suppose...
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Old 10-15-2017, 08:36 AM   #5
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If you can't or won't use a proper scan tool yourself, you leave little options as to diagnosing the problem, if there even is one.

The throttle position sensor tell the computer when your foot is off the throttle. If RPM are higher than the set current idle conditions, it cuts fuel. If it really was dumping that much fuel while coasting it would stall the engine, or you'd have a major hesitation as soon as you touched the throttle again.
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Old 10-18-2017, 03:11 AM   #6
sceh
 
Drives: yaris 2004
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I will hunt around for an ODB reader.
There is clearly a problem since my other cars have the normal behaviour of showing instantaneous fuel consumption when coasting to be zero after a few seconds whereas this is the exact opposite.
If it were true then the spark plugs would be gummed up by now and it would backfire on coasting so this is clearly some sensor misinforming the ECU - which one though..
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Old 10-18-2017, 07:30 AM   #7
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try disconnecting the battery for 30 seconds and see if that fixes anything. The car might run a little funny for a bit, but that's just the computer re-learning the fuel maps.
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