Short lean condition at Idle

[Warp10]

I've started having somesort of a lean condition since I went to the track last week.

The lean occurs after the car idle for 30-40 seconds, goes lean 17-20 AFR then slowly goes back to 14.7 AFR. Only occurs when engine is hot.

I could be driving for a while, get to a stop and problem occurs as well. Also after start.

O2's goes down to 60-70 MV and stay there until lean condition stops.

Check frames 450 to 650.

Thanks for any help.

[Warp10]

Please

[Billf6531]

My guess is that you have a cam and headers and that your O2 sensors are cooling off. You're also very lean at idle. Why don't you correct that.

[Warp10]

My guess is that you have a cam and headers and that your O2 sensors are cooling off. You're also very lean at idle. Why don't you correct that.

Thanks.

Yep. Headers and FMS13 cam.

Too Lean. What's a good AFR @ Idle?

[Billf6531]

15 works well.

[Warp10]

15 works well.

OK. My commanded is at 14.7 so I guess it's fine. Just don't know why my actual AFR will go from 14.7 and slowly climb to 17-20 and slowly back down to 14.7. As you said, It could actually be the O2's.

I'll put the car in open loop and take it from there.

[WS6FirebirdTA00]

what's the IAT doing? Could be heat soak since it happens on startup.

[Warp10]

what's the IAT doing? Could be heat soak since it happens on startup.

IAT is OK. Problem also occurs when driving and as soon as I stop at a light or stop sign, the A/F @ idle will stay OK for 20-30 seconds and then start to lean. Also tried with the hood up on a fairly cold evening. Same problem.

[WS6FirebirdTA00]

there is some pretty crappy modeling of hot start airflow and heat soaking that is one of the biggest culprits I think.

[Billf6531]

Playback your log and look at the O2 voltage when this is occurring. Your O2s are flat-lined low.

IAT is OK. Problem also occurs when driving and as soon as I stop at a light or stop sign, the A/F @ idle will stay OK for 20-30 seconds and then start to lean. Also tried with the hood up on a fairly cold evening. Same problem.

[WS6FirebirdTA00]

all that does is verify that it is lean. If the car was that lean, it would make the o2s flatline (unless they were flat lined rich causing fuel to be pulled)

[Warp10]

there is some pretty crappy modeling of hot start airflow and heat soaking that is one of the biggest culprits I think.

Good tips. THX

I reviewed my log and the IAT was between 80-81F steady while AF went up and down and throughout the whole scan.

As for the Idle airflow tables, I didn't change it before going to the track. And before I went there, I didn't have this lean condition.

Could there be anything else?

[EC_Tune]

The +25 LTFT in Cell 20 at frame 468 could be part of the issue. Then when it drops to Cell 19 the STFT's there start climbing pretty hard as well. I would do a bit of VE and MAF tuning around that 1200 RPM area and see if things improve.

[Warp10]

THX I noticed I did my MAF tuning with the LTFT enable. Live and learn I guess. I'm redoing the tune from scratch. So far so good.