Miss at Idle: Failed Emissions Test

[Lee_Burough]

Failed Emissions, Please HELP

Drove my Stock TTA 600 miles yesterday. Car was perfect when I started and had a minor miss at idle when I got home.

Emission Test Results: Passed the Fast Idle portion of the emissions test (135.0 PPM HC), but not the idle portion (527 PPM HC). Passed the other tests and the visual.

Got new plugs (43CRTS) to install tomorrow. Checked the plug wires good with impedance under 1k ohms. Put butane gas, via unlighted torch, around all the vacuum lines I could trace, no difference (it did sound a lot like other vacuum leaks I've had in the past).

If the plugs do not cure the miss, I'll look for some other things. Could I have an injector problem?

Any suggestions? ....Thanks

 

[gofstbuick]

What are the rest of the readings? CO, CO2, O2. If your car was tested with a dyno, what are those reading? HC is unburned fuel, and the readings you provided are quite alot.

 

[Lee_Burough]

Thanks for your post, gofstbuick.

Other emissions data as follows (no dyno):

IDLE 2500 RPM
HC PPM 527 135
CO% 0.86 0.84
CO2% 13.7 13.9
RPM 746 2558

An update on low idle miss: Plugs were the perfect color with a gap of about .030 (regapped to .035 and reinstalled those plugs.)

Fuel pressure (everything still hooked up) was 42psi at idle. 32psi 13 minutes later and still 32psi 22 minutes later. What does that tell me about the injectors?

Thanks again...

 

[gofstbuick]

The CO2 readings for your engine should be 14.5% or higher. That looks a little lean. If you have access to a smog machine, use manual mode and introduce propane into the intake or snorkel (with the maf connected, or in front of the maf). If the HC begins to drop (toward a passing range) then you're lean. You can also verify lean by looking at O2 voltage, in closed loop, the sensor voltage will be low (350 mv or less). If you have access to a lab scope or graphing multimeter, a the O2 sensor will reveal a misfire by hash marks on the O2 voltage line(indicates puffs of air that a misfire creates by not firing the mixture)

 

[gofstbuick]

Also, I hope you're not trying to lean the mixture to pass a smog test, because our engines run inherently lean from the factory.

 

[Lee_Burough]

Passed emissions with new oxygen sensor, injectors and RA 93 chip, plus several precautionary changes like fuel filter and the like.

Thanks to all who helped finger this out via emails and PM's

 

[gofstbuick]

I'm glad your car passed.