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Old 03-23-2006, 02:21 PM   #1
Scooby Newbie
Member#: 73755
Join Date: Nov 2004
Chapter/Region: MWSOC
05 STI

Question Idle AFR's with JECS Injectors?

I recently installed JECS 720cc injectors on my 05 STI. My UTEC is set to 740 (stock 550) injector scaling. I've logged ST and LT trims over a 150 mile drive. Things are looking good with LT around -3.5 and ST between -5 and +5 depending on RPM and load. At idle (~700 rpm) however, my wideband shows AFR's at 11.5-12.1 and I can't seem to get it any closer to 14.7. My guess is that I am running into a "minimum injector on-time" problem. Using the TARI OBDII reader, I can see the injectors are firing at 0.9% duty cycle and I can't get it lower than that. I've experimented with setting the injector scaling up to 930cc and I've also tried setting the fuel map to -10 in the 0% column at 500 and 750 rpm. Neither of these changes have had any effect. Oh, also at idle, my ST trim drops to -25.

Has anyone else run into a similar problem? I can see this problem being ignored by tuners since the car idles fine with no smoke or other problems. I only noticed it because of my wideband (and the stock O2 showing similar AFR with TARI). And there's a periodic, pesky P0172 code if the car idles for a long time. Periodically resetting the ECU just doesn't seem like the right answer.

Thank you in advance for your help.
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Old 05-04-2007, 09:49 PM   #2
Scooby Newbie
Member#: 54871
Join Date: Feb 2004
Chapter/Region: International
Location: Costa Rica
1999 Impreza GT


I put 720 cc injectors in my MY99 Turbo 2000 cc engine and I was able to find 14.7 at idle with the apexi SAFC2, with around -10 % setting at 800 rpm

I honestly helped ECU with the mechanical pressure regulator setting to 30 psi (at iddle vaccum -15 inHg) to make this easier.

You may do that with your ECU setting too...
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