Overrun fuel cutoff - not happening!

dr_jones
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Joined: Wed Jun 08, 2016 3:24 pm

Overrun fuel cutoff - not happening!

Post by dr_jones »

Any ideas on what could cause Overrrun fuel cutoff to *not* happen.

Seems fairly simple - ie engine drops below 'Engine Speed' (in my case 3K rpm) and the throttle is 'closed' (in my case <5% opening) - and the fuelling should be cut that is until either the throttle is opened or the engine speed drops the 'Engine Speed Hysteresis' (in my case 200rpm) below 'Engine Speed' (so @ 2800rpm then).

However I'm not seeing a fuel cut situation - rather I'm seeing around 15 ish AFR and a fair amount of quiet overrun popping.

....any ideas?
stevieturbo
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Re: Overrun fuel cutoff - not happening!

Post by stevieturbo »

In logging or on screen, is the throttle actually recognised as closed when it is closed ??
dr_jones
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Re: Overrun fuel cutoff - not happening!

Post by dr_jones »

Hi - yes it is - at least tpsclosed is being indicated (LED type gauge withing SMon) - fuelFinalPri1 is also indicating I'm seeing around 1.7 + ms of injector opening during at times when I thoretically should be seeing fuel cut.
pat
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Re: Overrun fuel cutoff - not happening!

Post by pat »

Overrun fuel cut off happens if the engine speed is over the Engine Speed threshold, and it remains cut off until such a time as the RPM drops below Engine Speed minus Hysteresis. So if your threshold is 3k and you are at 2999 then you will not get cut, even though you are above the reinstate RPM. You would have to close the throttle at 3001 RPM or higher for a cut to happen.

If I have misinterpreted your original description and the above is already true then please fee free to supply a datalog and calibration of the behaviour you are seeing so we can find out why it is not working the way it should.

Hope this helps,

Pat.
dr_jones
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Re: Overrun fuel cutoff - not happening!

Post by dr_jones »

Thanks Pat and sorry - its my description in the post there that's wrong - yes I'd expect cutoff only above 3K rpm with tpsclosed and then reinstatement and 2800 rpm (irrespective of tpsclosed) - cal is here:

https://dl.dropboxusercontent.com/u/202 ... e%20v50.SC
stevieturbo
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Re: Overrun fuel cutoff - not happening!

Post by stevieturbo »

Looking at some old logs.

End of a run in 4th gear, letting off the throttle at high rpm to slow down.

Throttle is closed, rpm is above threshold....logged FuelFinalPri1 seem to follow map table values ( ie base plus whatever compensations might be active, but the numbers are higher than base )

So this would make it appear the ecu is still injecting fuel. AFR's do go very lean. Maybe not instantly but they are very lean. Whether that's just because the pulse widths are very small, or because no fuel is being injected not sure.

But you would think if fuel is being cut off, FuelFinal should indicate this ?
dr_jones
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Re: Overrun fuel cutoff - not happening!

Post by dr_jones »

Yes - that's what I've noticed also I don't *ever* seem to see FuelFinalPri1 go to zero would seem logical unless fuel cut just disables the injectors in some way rather than pulling FuelFinalPri1 to zero.
pat
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Re: Overrun fuel cutoff - not happening!

Post by pat »

Gents,

been away for a few days, will get a chance to look at this properly in the next day or two, but one thing that you can check in the meantime is trqFuelSev - something in the back of my mind is telling me that ORFC is applied using fuel-based torque limiting, so you would expect to see trqFuelSev go to 100% when ORFC is active. This would not affect fuelFinalPri1 - the computation is still valid, but at the last step it is just not applied to the injectors. Of course if you have setup ORFC and neither fuelFinalPri1 drops to 0 nor trqFuelSev goes to 100% then there is an issue. If one of those happens but the lambda reading does not go to fresh air then it may be residual fuel (if for a short time) or leaky injectors (if it just won't go lean).

Hope this helps,

Pat.
stevieturbo
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Re: Overrun fuel cutoff - not happening!

Post by stevieturbo »

pat wrote:Gents,

been away for a few days, will get a chance to look at this properly in the next day or two, but one thing that you can check in the meantime is trqFuelSev - something in the back of my mind is telling me that ORFC is applied using fuel-based torque limiting, so you would expect to see trqFuelSev go to 100% when ORFC is active. This would not affect fuelFinalPri1 - the computation is still valid, but at the last step it is just not applied to the injectors. Of course if you have setup ORFC and neither fuelFinalPri1 drops to 0 nor trqFuelSev goes to 100% then there is an issue. If one of those happens but the lambda reading does not go to fresh air then it may be residual fuel (if for a short time) or leaky injectors (if it just won't go lean).

Hope this helps,

Pat.
trqFuelSev does indeed go to 100%

But it would be nice for the cut to also be reflected in the FuelFinal PW value to ? Just as it makes sense really ?
pat
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Re: Overrun fuel cutoff - not happening!

Post by pat »

Stevie,

thanks for confirming you are seeing 100% trqFuelSev in your logs.

With regard to whether fuelFinalPri should drop to 0, that is a matter of classification. If we think about the steps taken to get to fuelFinalPri1, from the ECU's perspective it does not have control over any of it (well, OK, maybe under certain conditions)... it does not control map1 (the driver does), it does not control ect (the stat does), it does not control act (the intercooler does), it does not control the battery voltage (the alternator does). So all of these steps are the ECU reacting to readings to make sure what it is doing is correct for the prevailing conditions. On the flip side, torque interventions are entirely in the ECU's realm. It decides that an intervention is needed (launch, ALS, traction etc, but perhaps an external request too). There is no sensible way to represent the fact that some cylinders will not get fuel in fuelFinalPri (yes I know that ORFC at 100% is a special case) - the logs would look awful if they wiggled between the right fuelFinalPri and 0 during launch or ALS.

Since the ECU decides that no fuel is needed, ORFC logically falls into torque intervention and rather than code a special case to output fuelFinalPri at 0 when trqFuelSev is 100% it looks like it was just left with the generic reporting that can cope with any level of cut.

There seems to be some logic in there - even if I had to remind myself of it :)

Cheers,

Pat.
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