Got my AEM UEGO installed the other day and it indicates that I'm running pretty lean. Around 14.6-14.9 at idle and while cruising and it comes down through the rpms to about 13.2 at 6500 rpms (at full throttle).

My first thought was that maybe there was an exhaust leak where the cat meets the header, but everything seems pretty tight and secure. The sensor is located just before the drivers side cat.

My mods are:
Crawford plenum and cats
Z tube & K&N drop in
Fuji Legalis-r exhaust + Y pipe
Intake manifold coolant bypass & heat resistant gasket.

This ratio is high enough to cause me a bit of concern, anyone got any thoughts?

 

with your mods it is highly recommended that you get a s-afc and dyno tune it.. the uego should help out a lot with the tuning

 

I've been thinking real hard about getting the SAFC. Splicing into the ECU harness intimidates me a little. I need to order the service manual to see if I can figure out what I'm doing.

 

i forget who, but there's a vendor here who sells a harness that allows you to install piggyback's without splicing into the stock harness. it's a 1:1 with a male and a female connector. plug the stock harness into this, and then plug the new connector into the ecu.

stoich is right around 14.7, so 14.6~14.9 at idle seems reasonable. looking at your mods, the only thing that *may* have an impact on AFR would be the Z tube. if the diameter of the MAF housing is even a miniscule ammount larger it can cause leaner afr's, but even then i wouldn't expect to see the problem pop up at idle and low load cruising.

 

does anyone know who sells/makes the plug and play harness for the apexi s-afc?

 

Found it. That thing is a little expensive, but it could be worth it.

http://www.forgedinternals.com/store...cat=256&page=1

 

That A/F is just about right. Most naturally aspirated cars run close to 13.0-13.5 in the WOT A/F for optimum HP(with a good margin of safety) and 14.6-15.0 at idle and light throttle (for good gas mileage).

Turbo/SC'ed cars usually run safest between 11.5-12.5 depending on the setup.