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Required Fuel settings for boosted engines


dum-bass

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Should I set this required fuel AFR box to 14.7:1, or set it to my maximum expected AFR usage? I am using 30lb high impedence injectors and I noticed on Cygnus's msq posting, that he was using 45lb injectors and set his required fuel to something like 11.5:1. Is this the correct thing to do for boosted engines? I can't seem to find any info on this and the mega manual seems vague on this issue or maybe I really am a Dum-bass.

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OK, I saw that I had a few people lookin but no replies so I asked my Grand National guru buddy the same question and he said YES you do need to set the required AFR box to your expected usage so it will adjust the injector pulse width accordingly. The part that confused me was the mega manual says to put in the AFR for the type of fuel you will be using and nothing about your target AFR usage. In my case it was 11.5:1 not 14.7:1 in case anybody is interested....

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If you set the required fuel based on your full boost AFR, the pulse width may be too wide to get a proper fueling a low engine loads (depending on how large an injector you are using). I usually set the required fuel for 14.7:1, and then adjust it to get a smooth idle. Then adjust the VR table to tune across all other operating conditions.

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Pete, my issues arose when I had detonation under full boost, the Megalog viewer showed my ego running way too lean like 18:1 afr and pulse width was pegged at something like 10ms. I had my afr table set to 11:1 in that region and the VE table was @ 119%. I had the the the required fuel setting in the 'fuel settings, injector characteristics calculator box' set to 14.7:1. I'm thinkin GEEZ! I have 30 lb injectors and no reason to run that lean @ 8psi so after mulling it all over, I changed the required fuel setting to 11.5:1 and tried again. Now, I had no detonation and the datalogger showed ego afr in the correct region and pulse width @ 13 something ms. I did however, reduce the inj. open time to get it to idle good. I'm a newbee @ digital fi and am undergoing a huge learning curve on this. It could be that I have alot of my settings bass-ackwards but it seems to work for now.

BTW, I totally respect your input and dont want to steer anyone in the wrong direction with this so please don't hesitate to correct me.

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Are you using wideband O2?

 

With 30lb injectors, you will not have any idle problems, so go ahead and use a different target AFR than 14.7:1. In either case, keep increasing the VE table bins until you get the AFR your looking for. I've run VE bin entries over 160 without any issues.

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