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RX7 plugin S6 Weird Injector duty cycle


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I have some problem with the injectors fueling problem on a Stock FD3S with single turbo conversion.

Every time when the engine goes from negative to positive pressure around 100KPA the injector duty rise and fall back. It cause lean burning and the engine bog at the early beginning and i have to add way much more fuel around the transition area and it could run smoother.

Any ideas? attached the log and calibration for your reference.

Thanks in advance.





FD3Sinjectorproblem.pclx FD3Sinjectorproblem.llgx

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That dip in primary injector duty cycle happens at the same time as the secondary's come in. You need to play with the Accel Fuel setting in Fuel->Staged Injection->Staged Injection, you currenty have it set to 0. @Adamw might be able to help with suggested values.

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Its caused by the secondary injectors initially turning on at 2700RPM, but because it goes lean, the RPM drops below 2700RPM and the secondaries turn off again.  So I think there are a variety of changes needed to get things right.  Set accel fuel to 1.0 initially.

But, first thing I suggest you do though is confirm the sec/pri flow ratio is correct, this is critical before anything else will work correctly.  I suggest not just doing this by calculation as quoted injector flow rates are rarely accurate.  This is how I do it:

  1. Set the Sec PW lockout much lower - say 0.5ms.
  2. Set the whole staging table to 0% - so all fuel is injected by the primary injectors.
  3. Hold the engine steady at medium load/medium speed - say 3000RPM, half throttle for example.  Easier on the dyno but you can also do it on a hill or whatever if you have a driver.  Note what lambda is reading (or log and look later), while still holding at same speed/load, select the whole staging table and change it all to 100%.  It is now running only on secondary injectors.  If sec/pri flow ratio is correct, then lambda wont change when you swap between pri to sec injectors.
  4. If lambda goes richer when you change to 100% secondary then your sec/pri flow ratio is too small.  Make it larger and do the test again.  

Once you have that correct then give us a new log and I will recommend some changes.  


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Thanks Adam for your recommendation

I put the car on dyno, set the secondary PW lockout to 0.6ms(the minimum allowed by the software)

Set the secondary to 0 at 80 and 85kpa boxes. Rev the engine in 4th gear 3000rpm and loading around 60kpa. when i change the secondary to 100% the engine goes bogging with the injector duties like on as off as shown on the pic.

I tried dial down to ratio to 1.00 it bogs for once and then go pig rich..i tried the ratio 1.5,2,3,4,5 all of them bogging continuously. The larger ratio it bogs more seriously.

I guess i may have to further reduce the value of RPM lockout avoiding the secondary switching off maybe? 

Before doing this test i did dialed up the Master fuel from 12ms to 16ms and the engine behaves better during the transition. not sure it related to such issue.



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Ok, so I beileve FD stock injectors are about 550cc primary and 850cc secondary, so your Sec/Pri flow ratio should be somewhere around 1.55.  Not sure why you have 3.3 in there.  Set it to 1.55 and do the test described above to confirm.  Note it will go lean and stumble for a second or two when you change from primary to secondary doing this test - this is because we dont have the enrichment set up yet.  You need to hold it until it stabalises to see how much the lambda changes.  

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Thanks Adam,

The 3.33 was from the base map at the G4X folder. Finally i have set it to 1.4 which perform the best and stays on the same AFR after the lean spike.

For the Enrichment u described above do u mean the Accel Fuel at the stage injection tap? I have set it to 4.00 injection cycle its still spike lean during the transition. What else i can do to eliminate the spike?

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  • 2 months later...

Hey guys. I'm also having a similar issue, although my sec/Pri flow ratio is correct. I'm running stock primarys which are 550 and for secondary a pair of Bosch (0 280 158 827) 1700cc injectors. im also having a lean spike when i switch from the primarys to seondaries but stabilizes after a second or two, its just during the transition that happens, tried increasing the rpm lockout too although it d idn't help.  Don't have a log right now will send it asap. 


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Did you do the test above (oct 8th post) to confirm the sec/pri ratio?   It is important to do that as the quoted flowrates rarely work out.  Then adjust the staged accel fuel setting to get the transition better.  I would expect it to be much higher than it currently is. 


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