After re-reading the stickies on the 730 O2 constants and RBob's ECM Proportional Control from '02 (awesome write up dude!) I am still plagued by a delima on my 6E MAF system.

To bring you up to speed here...

You can look at my sig but it's an aluminum headed L98 with a mild cam (212/218) HSR intake etc. I am using TunerPro v5 and have an Innovate WBO2 gauge with the WB output in my data logs. I am working with the expectation that my WB readings are correct at idle. Stoich AFR is set @ 14.7 and I am running 10% alcohol fuel. I have been adjusting my O2 R/L mean, upper and lower tables to bring my idle AFR to ~14.7 to 15. Currently my mean O2 R/L is 635 at idle with upper/lower +/-35. 14.7 on the WB gauge is where my engine pulls the most vacuum @ 16hg. Idle speed is 650. I have been able to get the idle AFR perfect when up to full temp and BLM's are 128ish. After idling for about 4-5 minutes the BLM's start to drop to 118 and AFR jumps up to <16. It seems to stablize there but vac drops to 15hg and it runs less smoothly.

My question is "Why does the ecm start pulling fuel after idling for a while?" I suspect it is somewhere in my other settings like the reduction gains or filters but can't seem to get a handle on it. My gut call is that something is getting into a runaway situation mathmatically. Any suggestions on what to adjust will be greatly appreciated.

BTW I have deleted my EGR and AIR and have made the necessary changes in the bin.

 

Check the O2 signal, that is what the ECM will follow. I like to graph it along with RPM to get a better idea of what it is doing.

When an O2 sensor cools off it tends to report lean, which forces the BLM high. A silicone poisoned sensor reports rich driving the BLM down.

With the headers need to use a heated O2 sensor. If the tip of the sensor has a white almost fluffy substance on it that is silicone.

RBob.

 

Thank you I will check the sensor. I am using a heated O2 and have checked that it is getting power/ground. I am reading over your write up on ECM proportional control now. It is written for a different ECM/system but it seems to apply for the most part. I am still reallly trying to get it straight. If the problem still persists after the hardware checks out should I consider making changes in the slow O2 filter/low O2 filter/O2 error reduction gain vs airflow tables? It seems that the idle afr is just right (~15) until the ecm pulls fuel and the afr goes high. This only happens after a few minutes of idling.

 

Antman,
ever figure out what was the problem here?

 

Not really, I ended up building a different motor and running the EBL flash ecm. Now with a longer duration cam (and larger ci) I still have had a difficult time with closed loop. I run open loop during idle and closed loop at cruise with the PID dummed down some. I also bracket the BLM so it can't adjust farther than 120/136, which it does stay between. Don't know if that helps but it's what I've done.