405 MI16 fluctuating fuel consumption

[mi16pug]

Have been competing in various Tarmac Rallys of late and am getting interesting results on fuel consumption which is stumping me.

Last weekend, 2 day rally, same road and driving style average speed of 70kmh throughout the rev range up to 6500-7000rpm on gear changes.

Day1: 280km's, fuel usage 33.74L's -> 12.05l/100km
Day2: 279km's, fuel usage 18.04L's -> 6.46l/100km

Now that is nearly half the amount of fuel.....same distance, same (hard!) driving style, same roads, same fuel station filling up (98 octane...).

Car drove and performed (seat of the pants) same each day - now i'm worried that there is something fishy going on with the fuel injection and sensors resulting in the car running lean potentially causing an issue.

Ideas???

Geoff

 

[Stuey]

My idea is you made an error on the second day. It'd have to be very lean for you to get 7 litres per hundred driving flat out and if it WAS that lean it would have broken. IMO.

 

[TiMi16]

Did you run the course in reverse the second day?
Might be the wrong line of thinking, but is it possible day 1 was “uphill” and day 2 “down hill”?

 

[jo proffi]

Have been competing in various Tarmac Rallys of late and am getting interesting results on fuel consumption which is stumping me.

Last weekend, 2 day rally, same road and driving style average speed of 70kmh throughout the rev range up to 6500-7000rpm on gear changes.

Day1: 280km's, fuel usage 33.74L's -> 12.05l/100km
Day2: 279km's, fuel usage 18.04L's -> 6.46l/100km

Now that is nearly half the amount of fuel.....same distance, same (hard!) driving style, same roads, same fuel station filling up (98 octane...).

Car drove and performed (seat of the pants) same each day - now i'm worried that there is something fishy going on with the fuel injection and sensors resulting in the car running lean potentially causing an issue.

Ideas???

Geoff

I agree with stuey,
You have probably made a measuring mistake.

2l petrol engines driven hard don't get 6l/100km economy (unless its all downhill).
12l/100km is a reasonable number.