I did a search on this but could not find this specific problem discussed.

I have been tuning an ANLU VE map for my 350 TBI w/ vortec heads (cam, headers, exhaust).

While driving (I drove for 1+ hour), my BLMs are reasonable: 128 +/- 2 or so. After getting back home, I had the car idling while I saved my various Winaldl tables. During this time, I noticed that the BLM at RPM1200-MAP30 (idle RPM-MAP), dropped to 117 (previously at 128 or so).

I looked at the real time WinALDL data and BLM was steady at 111, and the BLM average value (latest readings) kept dropping to reflect this.

Could this be an IAC settings problem or could the O2 sensor (it is new) not be giving good readings at idle for some reason?

Just wondering if anyone else besides me has seen BLM register at 128 (or close) while driving and then read rich at sitting idle.
Or if you know of a thread discussing this topic that I missed-

Any help is appreciated.

Thanks,
S-D

 

i belive in the speed density chip there is a value that can be adjusted to get the ECM to register rich or lean at a different O2 voltage. it has been discussed before, and is helpfull for large cammed engines because they are ecential pumping unburnt air into the exhaust from overlap and it makes the ECM think the car is running lean, thus the addition of fuel at idle.

 

Normal.
As the engine sits and idles the oil gets hotter, the coolant gets hotter, and the manifold gets hotter. The hotter the manifold the better the vaporization. ie the easier and better the fuel burns. So what was fine at 110dF MAT temp, is slightly richer reading at 140dF. As long as you within a resonable amount of change your fine.

One reason to run a valley pan on a street car.

 

huh and to me it sounded like mayeb the o2 sensor was cooling off. there not much exhuast gas avauable to keep it hot.

 

Nope.
Symtoms don't match.

 

I had not considered a physical/chemical phenomenon as suggested.
It seems to provide a logical explanation.

I guess for an emissions test, I'll have to split the difference (n the VE table, favoring idle) since the car is tested at idle and under load.

Thanks for taking the time-
S-D