The car is at STM now getting looked over this weekend, but I wanted to try to figure some of this out, and help them diagnose.

Symptoms:

• Car seems to run fine while driving, but when I get to a stop light, the car stalls out on decel
• Plugs are BLACK!
• Log shows that at idle, the car is adding 15% fuel, but we aren't totally sure why

Mods:

• HKS 280 cams
• manual boost controller and STM tune
• brand new Denso front o2 sensor from rockauto.com
• stock everything else

Possible causes??

• vac leak?
• o2 sensor is bad, since it's not OEM
• stuck EGR valve
• anything else??

Please let me know if you have any ideas. The car has stock injectors, and the scaling is all correct, so I am kind of stumped here. Emery has a hunch that the denso o2 sensor is bad, and that is causing it to add fuel, but it's weird since it's a Denso, and that is a great brand (stock sensor is denso I think), and it has a total of like 8 miles on it.

-mark

 

Since the sensor is such an easy swap and they probably have a few laying around, swap them out and write it off if it doesn't fix your problem

 

also, make sure that your ECU is not putting your car into open loop at idle.

 

The ecu doesn't command fuel trims in open loop, that would defeat the purpose of going into open loop.

 

A new component does not mean a functioning component. Especially an O2 sensor. Don't overlook a part because it's new. Until you've actually tested it, assume that it could be the problem.

 

obviously, but maybe his ECU is set to go into open loop at that point and is adding more fuel.

its just something i would check

 

This has bitten me more than once. O2 sensors are really easy to test too.

 

Putting in an OEM o2 sensor seemed to fix the problem, but then later in the day, I got a CEL for P1400, EGR. After checking everything over, my MAP sensor was wired incorrectly. The yellow and grey wires were flipped around, so the signal and power wires were reversed. After fixing this, my P1400 went away, and the EGR functioned properly.

I am not sure if the MAP being wired incorrectly could have caused my fuel issues to begin with or not. Just out of curiosity and to learn what how it all works, does the MAP do any fueling modifications at idle, or at cruise like my original problem of adding 15% fuel?

-Mark

 

it shouldnt as far as i know. as long as you are in closed loop at idle and cruise, your ECU is reading your O2 sensors for their AFR's