a mechanic hooked into the car's brain today to check the a/f ratio. we found that the primary o2 sensor is causing the ecu to lean the a/f ratio at idle and constant rpm driving. the car is not throwing a cel and doesn't show any other outward signs of running lean except for white spark plugs. the only changes under the hood are a k&n filter, a toda header, and the smsp carsound cat. i plan to get a vafc to richen the mix, but a stock R running lean could point to another underlying problem such as a intake manifold vacuum leak.

any thoughts on the header causing it to lean out?

 

Easier flowing engine allows more air into the engine. This will lean out yor af ratio because there is more air entering in. You ECU will do some compensating.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 98TypeR &raquo;</TD></TR><TR><TD CLASS="quote">Easier flowing engine allows more air into the engine. This will lean out yor af ratio because there is more air entering in. You ECU will do some compensating.</TD></TR></TABLE>

hmmm, that seems backwards because my ecu is actively leaning the fuel mixture. if the o2 sensor saw the motor was running lean via the exhaust (your example), the ecu should add fuel, right? my ecu is removing fuel.

what is next to check? can a header cause the ecu to lean the a/f mix?

 

for help.

 

I run lean with my spoon header, white plugs and all. Put my stocker back on and the plugs were perfect. I now richen it up with my VAFC for partial throttle settings and idle. I jump from like 280miles a tank to 350 a tank with a header!

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Rguy &raquo;</TD></TR><TR><TD CLASS="quote">I run lean with my spoon header, white plugs and all. Put my stocker back on and the plugs were perfect. I now richen it up with my VAFC for partial throttle settings and idle. I jump from like 280miles a tank to 350 a tank with a header! </TD></TR></TABLE>

A header will make that much of a difference in mileage?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by NunRacer &raquo;</TD></TR><TR><TD CLASS="quote">

A header will make that much of a difference in mileage?</TD></TR></TABLE>

Thats what i thought. But it does. I can easly get 70 more miles per tank just by swapping header and cat/test pipe. Ive had the JDM 4-1 and now spoon and both had same results on milage.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by NunRacer &raquo;</TD></TR><TR><TD CLASS="quote">

A header will make that much of a difference in mileage?</TD></TR></TABLE>

weird, hun? even wierder is the toda/jun cam guys reporting an increase in mileage.

i'm getting the funds together now to buy the vafc and some sgt quality dyno time. i've just never heard of anyone using the vafc to add fuel to a mostly stock R.

 

stock cars runs a little rich...

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by DeL SLo &raquo;</TD></TR><TR><TD CLASS="quote">stock cars runs a little rich...</TD></TR></TABLE>

right, and now mine runs lean with just a header.

i guess no one has checked their a/f ratio after adding a header?

 

Stock ECU has limitations. Maybe your header is making your car run that much leaner and the ECU is compensating the best it can. I dunno just a suggestion.

 

you guys have to learn how to use a scan tool. you can check your short term and long term fuel trims and adjust with a fuel pressure regulator. the short term trim fluxuates with driving conditions. if it's constantly reading with a - in front of the number it means the car is rich and the ecu is trying to pull fuel by shortening the pulse. the long term ideally should be +- 5 meaning either -5 or +5 with zero being ideal {so they say} i personally try and tune cars around -3 with the FPR. the ecu can easily make up the difference and it helps with hot summer days. if you start getting a long term above 10 after driving 100 or so miles you need to adjust one way or the other. if it's -10 or more you need to lean out, if it's 10 or more you need to turn up the pressure and richen up. the first live data scan you do should tell you quite a bit about your car. remember, the ecu corrects for these conditions with the 02. if it gets too far out of wack you can help the car by adjusting. CEL's come when the long term goes too far one way or the other.

this is probably a necropost but i still get asked this question often and there is a lack of tuning advice on the obd2 stock ecus on HT

 

why would you bump a thread thats 5yrs old....and who tunes using the FPR. Just switch to OBD1 and get it tuned the RIGHT way.