2 vehicles i have upgraded primaries on seem to not respond to the BASE and INJ fuel maps after swapping in larger primaries, i generally stick to close to stock size primaries but these setups required larger injectors. i have adjusted the lag to various setttings to smooth out the running of the engine but the BASE and INJ maps have 0 control over the fuel input and they run pig rich (9-11 AFR) while in vacuum and i just can't figure out what the hell is causing the PFC to ignore the inputs from the fuel maps while trying to lean them out.

1 is an FD which i had installed 850's in the primary slots with the original impedence side feeds, 1 vehicle is an FC with an adapter harness for an S5 with i installed low impedence 1000's in the primaries. the FC actually took to the larger injectors better than the FD did but through all my searching i haven't found any info as to why the maps are not correcting for the larger injectors.

using the beige box and tried several different versions of FCedit with no changes. running negative lag for the primaries smooths out the running but then it has a hesitation when more fuel is needed due to the lag in response time from the injectors, not a cure but it helps.

for example i can set the INJ maps to 1.00 correction factor all across the board and set the BASE maps to .002 pulsewidth and the injector pulsewidth is still hovering around 6milliseconds at 1k RPMs off idle and no matter what is edited there is no change to bring it down.

fuel pressure is at a modest 38psi and the injectors are brand new, both vehicles respond identically so perhaps i am completely missing something.

 

It is well know amongst us more experinced PFC users that the PFC will only allow an "unkown" minimum primary injector on-time.
When running large primaries, this built in limit results in them not being able to be leaned out properly using the nomal fuel tables no matter what you try.

That is why many of us do not recommend them for steet use. OK for race cars which are basically idle and full power.

There is only one way to lean the idle out. First lean them out as much as posible with the fuel map for the idle area only.
Then you reduce lag which does work!

This makes the injector act like a smaller injector which messes up the PFC internal sequencing from primaries to all injectors.
Thus you should play around with changing the primary injectors size or % to counter act this.

Unfortunately neither TWOKRX7 or I have had the chance to fully tune such an engine to document the full details.
We plan to test them fully in the not too distant future if the owner does not change his mind.

 

i figured it was something such as this, another reason i really do not prefer the PFC for any real performance builds.... oh well, i did figure out playing with the lag will help the engine run naturally smoother even while not pulling the AFRs up any at all, it is just injecting the fuel later after the port is near closing to help reduce fuel fouling from overly rich mixtures. then you have to play with the accelerator pump features to make up for the lean spots on accel due to the increased lag....


what a pita!

thanks for the clarfication of what i was afraid of though, such is the life of building a 500+whp car on a limited setup.

i suppose i can have him switch to 720 primaries, i just prefer a safer setup for a larger turbo since with the 550's/1200's it was running out of fuel on a smaller trim turbo however that was with the crappy FD fuel pump and stock regulator installed too which really only limited it to about 300 or so whp.

new setup is a 255LPH pump, Methanol/Water injection, 1000/1200's, Aeromotive FPR, MP T70 turbo.

tough to get it to idle and not lag when accelerating or cruising with such large primaries and the PFC, so maybe he may have to step back down a little to the 720/1200 or a 550/1600 setup however i hate such huge gaps in injectors from pri to sec.

 

I run 550/1600 with a MJO driver running the 1600s on my mild port GT35R setup.
I do not have any transision problems at all.

There are other PFC injector parameters other than size, %, and lag.
Using them all makes the difference!

 

i know it's possible to transition them, it's just easier to transition with a smaller gap. i just wind up getting cars with upgrades that already have 1200-1300 secondaries, kind of a waste to pull them out and replace them with 1600s but that seems what you have to do with the pfc.

 

YES ther are many idiots out there who think larger is the only way to go for everthing!

It is our DUTY as informed mechanics/tuners to set them straight even if they do not like it or decide to take their piece of trash someplace else.

I do not kiss ***.