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Injector Staging and Effect on AFR

Practical Standalone Tuning

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My car was mapped to 1 bar by the previous mapper on the default RX7 Link G4 Base map but the injector fuel staging was not optimized for my setup and the sec/pri ratio was left at the default 3.3 as supplied by link for the s6 rx7 base map.

I noticed this and have corrected the values as per the Link g4 plus sec/pri ratios and remapped the car to 1 bar myself. The only thing I've noticed which is different is previously on the logs after a 4th gear pull when the throttle was closed the afr would drop and hover around the 12-16afr, this is on closed throttle after the 4th gear pull.

However with the accurate sec/pri ratio and the car remapped to 1 bar, I am noticing after a 4th gear pull when the throttle is fully closed the afr reads 19 consistently now where as before after a 4th gear pull when throttle was closed it never read 19afr, is this normal now the sec pri ratio has been changed to the more accurate numbers? and the asnu 1500cc sec inc spat data added as supplied by asnu.

I have attached the logs of the afrs before and after.

Kind Regards,


Attached Files

sound to me like you activated the fuel cut when off throttle, while it was not cutting fuel on decel with your old tune...

is there a way you might have change something related to this? if load value in vacuum was "off" before, maybe it was not getting into decel fuel cut mode because of load value? I would investigate along those line.

The difference is coming from mostly a change in injector deadtimes, possibly a little from short PW adder, but that is not loggable.

Below I have overlayed an area of simlar operating conditions from the two logs. The pink traces are the old tune and the coloured traces are the new tune.

In both cases the secondaries are off so it is nothing to do with the staging settings. But if we look at the values reported where the cursor currently sits in the time plot, RPM is similar, MAP is similar, fuel table number is similar, Injector effective PW is similar, but Inj actual PW is quite different - you have about an extra 0.3ms coming from somewhere, looks like about an extra 0.4ms from deadtimes and -0.1 from SPWA.

Effective PW is what the engine should be getting - actual is what is being applied to the injector to achieve that. The difference between actual and effective is the short PW adder and the deadtime.

Having said that, I wouldnt normally be worried about AFR on over-run conditions as there is no load. If you are running pre-mix rather than oil injection it might be more important but I dont have enough rotary experience to say.


It was the over run fuel cut which was adding the extra 0.4ms from deadtimes and -0.1 from SPWA. Thank you both and Adam thank you for looking into the logs, Issue resolved.

No it wasnt, overrun fuel cut wasnt active at all, and it wont change deadtimes even if it was.

Thank you, I also checked the log and the overrun fuel cut status shows does show off. I have checked the map itself and it was on turned on so I'm not certain why it shows as off in the log? I will do a 4th gear pull tomorrow with this turned off in the map and verify if on closed throttle if the afrs drop to 19 as they are currently.

Failing this, the data I changed was the data for the ASNU 1500c injectors as provided by ASNU themselves for the link ecu; for the injector deadtime table and sec inj spat table.

Perhaps your overrun isn't active because the throttle is at 1.5%, you might check the conditions for the Overrun Fuel Cut to be active...

As per Davids comment, there are conditions that must be met for ORFC to activate. Usually an activation delay and a maximum TP or AP threshold.

So if your dead times have been changed but your injectors haven't been changed then that would suggest at least one lot of your settings is/was wrong. Obviously you are going to get a large difference in delivered fuel when the commanded effective PW is only 0.5ms and you have changed the deadtime by 0.4ms, that is a large proportion of the PW...

Thanks David, It was set at 1.2% so likely it did not meet the conditions.

Adam - just to give some context to this situation so I can figure out exactly what is causing the afr to drop to 19s on closed throttle.

I had the car mapped by a very experienced mapper in the UK but he did not optimize my fuel staging, the numbers were left at the the link base map settings for the sec/pri ratio and sec inj staging table. Due to this my injector duty was hitting over 95% injector duty on just 1 bar of boost.

I noticed this oversight and changed the sec/pri ratio to suit my injector setup, which is oem 2x550cc primaries and ASNU 2x1500cc secondaries. Once I changed the numbers as per the link ecu formula. I changed the sec/pri from 3.3 to 2.72 recurring and the sec injection staging table from default link values to 73.7% from 18 psi onwards. I remapped the car myself and this resolved my duty cycle running out. I am now able to deliver 10.5 afr at 7300rpm with 80% duty cycle at 1 bar boost.

While optimizing further I changed the ASNU 1500cc sec injectors spat table which was zero'd out before to the below which is the data provided by ASNU. The points beyond 0.875 are zero.


I also changed the injector dead time table from the default link g4 s6 base map values to the below which was provided by ASNU. Perhaps these values are causing the afrs to drop to 19 on closed throttle after an acceleration pull.


I was unable to do the testing today but I will do a test tomorrow to confirm if the issue still persists.

Issue resolved - I have gone back to oem dead time table for the primaries and asnu's for the secondaries. Also turned off the ORFC. Afr's no longer drop to 19s on closed throttle after an acceleration run.

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