MoTeC Global Forum

Hi Guys,

I am trying to work out how this is calculated as I am getting some inconsistent readings.

The channel (Fuel Used M1) when logged in i2 shows in (ml) and seems to be a raw value from the M1. After doing some testing at the track it seems the value it returns is not very accurate or consistent from session to session.

I confirmed this by doing some manual testing. i.e. completely drain system, put in exact 20lt of fuel, run session, drain tank completely and calculate fuel used.

When compared to the Fuel Used M1 reading I could not get a consistent read. I was hoping to at least find a consistent difference % so that I could adjust using the fuel usage math in the dash logger.

For example:
Session 1 - M1 channel says I used 23.8lt when I manually calculated 16.5lt. Difference = -69%
Session 2 - M1 channel says I used 21.3lt when I manually calculated 11.9lt. Difference = -55%
Session 3 - M1 channel says I used 9.1lt when I manually calculated 10.8. Difference = +16%
Session 4 - M1 channel says I used 10.8lt when I manually calculated 11lt. Difference = +2%

Any ideas why the results would be so inconsistent?

Cheers,
Trevan

Incorrect injector dead time can play a roll but those numbers are wildly inconsistent... Are you using secondary injection? Is it direct injection? Are you monitoring fuel pressure? Lot's of variables could cause small errors but I've never seen anything like that.

Hi Ben,

Thanks for the response mate. No secondary injection or direct injection in this case and fuel pressure remained consistent and never dropped into alarm for any session.

Yeah it's the inconsistency that is throwing me. I am confident that I measured correctly but will be doing another test in the coming weeks to re confirm. Maybe there a better way to calibrate than the process I used?

The first thing to make sure you have right is the Injector Calibration, if this doesn't match your injector the fuel used will just never get close.

If you log fuel pressure at the maximum rate possible in the ECU you will see just how much it fluctuates. You will actually be able to see pulses in fuel pressure as each injector opens and closes. This is essentially the biggest problem with calculating Fuel Used, there is no way for us to know exactly what the pressure is at each injector at the exact moment it opens.

What sort of fuel setup do you have?

Hi Adrian,

Yes you are spot on... it looks like my injector calibration is not 100%. Fuel setup is pretty straight forward, running e85 with a surge tank and rising rate fpr. I can confirm base pressures are in check and correctly defined.

I am running FIC 1100cc saturated injectors and I can’t confirm if there is a pre defined calibration in the ECU for these. Closest I could find is a definition for an FIC H0011.1.0 which looks like it might be right however digging a little deeper into the calibration it seems flow rates for that is more like 1400cc??

Cheers,
Trev

Hi Trev,

If you have the actual injector part number I can check it in our system to see if we have done it.

Adrian

Hi Adrian,

FIC IS126-1100H

It doesn't look like we have done that injector. If you want it added you can organise with your MoTeC Dealer to get it sent in for characterisation.

Thanks Adrian will organise with my dealer. Appreciate the help as always.