Hey guys. Wondering if anyone here has done any testing with larger fuel injectors and an afcII. I have been running the afc on my evo with 3" exhaust, MBC, injen pipes. On 116 racegas the car traps consistent 108mph. I have a palm wiht OBD2 logger. Im getting about 20-21* ignition timing at the top of 4th and 3rd gears. Airflow signal is around 27.5-28.9lb/min with the AFC set at -18 from 4500 up. A/F ratio is showing mid to low 12's through 3rd and 4th. Timing is always advancing with RPM so I don't think the ecu is seeing much knock. Boost is spiking to 22 dropping to 19 (i do have a minor leak at the stock bov)

anyway...If I lean it out past -18 I don't see any increase in trap speed and the AF starts to get around 12.8-13.2. Timing doesn't change much at all.

So..has anyone used a set of say 650cc injectors and lowered the airflow signal down alot more with the afc and seen an increase in ignition timing and power/trap speed? Obviously I don't need the additional fuel supply yet, but the injectors could show some improvement from being able to lower the airflow signal some.

Im eventually going to get an AEM (probobly next month), but I would like to get all I can out of the AFC before I switch over.

Any Advise?

 

Oh yeah...
ECU is stock...no reflash (unless previous owner did it)

Would a reflash serously benifit in the timing department. The Fuel side of a reflash I could care less.

 

Do you have any issues hitting fuel cut with that combo?

 

Yes, If I try to tune it to run any richer than 12.2-12.3 I get fuel cut at 20psi or higher. It's fine on racegas, but Im not happy about running 12.3 and leaner on pumpgas everyday. The car seems to make a little more power at a richer setting as well. It felt stronger on the way home from Etown EVOvsWRX race after getting 5 gallons of 93 than it did right after leaving the track with 116 in it. I checked IGN timing on the palm and at the top of 3rd gear after getting 93 octane, the ign timing looks identicle to when it has 116 in it.

think i may run it on pumpgas this friday to see.

unfortunatly I picked up a Forge bov to test and have a greddy fmic on the way this week. I will be very tempted to screw up my fuel/tuning testing by putting those on. no back to back results.

Oh yeah...I did hit 109.49 mph on one run and 109.2 at Etown on saturday in worse conditions than at Island. I was running with the boost right at 20 and AFC set to -14 from 4500 up. A/F seemed to be right at 11.9-12.0

IT's odd I dont' hit fuel cut at the dragstrip, but do on the street going wot froma roll with the same settings. Airflow mush be just a little higher at the torque peak, since you don't get down to 4000rpm on the track.

 

You may be hitting "Boost cut" and not fuel cut.. Did you notice if you got a CEL recently? Boost cut is similar to fuel cut but it is caused by a sudden spike of boost and doesnt happen if the rate rises gradually.

Your right about the additional timing, reducing the MAF signal by 15% or more, makes the car think its running significantly leaner which indirectly affects timing.. you won't see much more than 21 degrees however..

15% reduction in signal should have raised your fuel cut point by about 10% (rough guesstimate)

Now, fuel cut seems to kick in around 1800hz depending on engine load and throttle position (also the factory ECU seems to be aware of Gear, indirectly calculated by speed vs rpm) and does seem to behave differently depending on the gear your in.

I think this is why the Buschur injectors are 680cc's since they are large enough to offset the MAF signal enough to be rich without inducing fuel cut in most circumstances.

But with a boost spike, under torque peak, you can see fuel cut if the conditions are right. However I'm more inclined to think you may be experiencing spark quench (misfire) because of the boost spike.

 

So, what does boost (not fuel) cut feel like? I just installed a turboback on my car and whereas before I was peaking at about 19-20 psi and tapering gradually to 17 or so, now it peaks to 21 but drops like a rock to 16. I'm going to keep testing it to see if it's consistent. I don't run a boost controller because I can't in my autocross class.

Thanks.