S15 running lean

[Flex2003]

1999 s15 spec r

Front mount ic kit
Turbo back 3"
Turboxs bov
Walbro fuel pump
Greddy oled boost controller
Aem uego afr

Just installed my aem uego this morning and at warm idle
Afr is 14. I expected to be like 11 or something and running rich. So i didnt even bother to drive it. Anyone ever heard of that

[Fuego]

That's a pretty normal idle AFR for SRs IIRC.

[ultimateirving]

at idle it's not under any load and will idle or should idle around 14-15 and kinda sweep between the two. Under boost it should be around 11.5 for 91 and hold pretty steady

[Flex2003]

Okay, that puts my mind to rest, it was hitting 12 in full boost 14psi. Im just new to s15s. Most cars run rich on idle in my experience. Thanks for help guys

[Dboyizmlg]

Okay, that puts my mind to rest, it was hitting 12 in full boost 14psi. Im just new to s15s. Most cars run rich on idle in my experience. Thanks for help guys

S15 motor correct?
If so, I believe 12a/f at WOT is ok. Considering there high compression.

I may be wrong though... I have S13 SR and at WOT mine is 11-11.5a/f

[Dboyizmlg]

You pump 91 or 93 octane?

[Flex2003]

91, it hit high 11s to 12. Anything below 12.5 should be fine i think. No ?

[Dboyizmlg]

Sounds about right, yes anything at 12.5 and above is no good!

[zurud]

No efi car run rich at idle. Target afr is 14.7 at idle and cruise

[Tom N]

S15 sr20det is the same 8.5:1 compression that a S13/14 is.
14ish afr's at idle is normal for any car.

[Dboyizmlg]

S15 sr20det is the same 8.5:1 compression that a S13/14 is.
14ish afr's at idle is normal for any car.

He is right. Compression is 8:5.1 same on all SR.
I don't know why I assumed the S15 had higher comp

[Kingtal0n]

I keep mine around 16.2:1 highway cruise, 3000rpm with 37-39* BTDC ignition timing, even with 270*+ Duration camshafts and mega head work (low vacuum cruise 6" Hg) I get about 34 mpg with A/C

[Dboyizmlg]

I keep mine around 16.2:1 highway cruise, 3000rpm with 37-39* BTDC ignition timing, even with 270*+ Duration camshafts and mega head work (low vacuum cruise 6" Hg) I get about 34 mpg with A/C

34mpg!
Wish I had that kind of gas mileage on my SR.
I'm assuming that's highway MPG?

[Kingtal0n]

lol yeah, city mileage is trashed by the cams. I might get 18mpg city, it depends what you define as "city". If there is alot of stop and go, and speed bumps, like at school or in a neighborhood, the mileage will be very poor (below 15mpg). But if I can cruise around the "city" in 4th gear around 42mph I can squeeze 23~ mpg out of it.

[Dboyizmlg]

Your highway mileage is really good compared to mine, that's for sure!

I have small stage 1 cams on mine so city isn't bad, I would say 18-22mpg city.

[Kingtal0n]

Your highway mileage is really good compared to mine, that's for sure!

I have small stage 1 cams on mine so city isn't bad, I would say 18-22mpg city.

What really improved highway mileage is timing. You need at LEAST 36 btdc cruising. I would shoot closer to 38 or 39.

When it was at 31* mileage was much worse, like 23mpg.

I spent a long time data-logging to figure this out. its pretty simple though, you just log injector duty cycle and fuel pressure for a lloooooong time. and add timing slowly. If your chart slowly gradually drops off in duty cycle and engine vacuum improves (fuel pressure is seen to drop) you are using less and less fuel at the same speed. cruise control helps.

[Dboyizmlg]

Thanks for the heads up!

When I get a re-tune I'll let my tuner know.

I would love to get more mpg on the highway!