I rebuilt my motor over the summer and switched over to using the ARAP bin. Ever since it has become cold here, they switch over to the winter blend of fuel. When I use the winter blend with 10% ethanol present it always sets off a lean code check engine light. If I were to lower timing at normal driving speeds, would it fix this problem? It just bothers me knowing that light is on.

 

hmm..... roughly 4%(14.7/14.1=4.25%) more fuel needed for using E10 vs E10 to maintain stoich. i wouldn't think the calibration would be that close to the edge.

lowering timing MIGHT fix it, but it might also make it worse. i would just loosen up the max BLM allowed to let the ECM deal with the change in AFR. 5-6 BLM counts should be enough compared to where you were before.

if you happen to run into E10 year-round, changing the stoich AFR to 14.1 would also accomplish much of the same result, just without requiring closed loop to be active to account for the difference in stoich AFRs.

 

BLM has a lean limit of 160 I recall in the GM code. 160/128=1.25 So the ECM has a winddow to add a lot of fuel. May be another issue... fuel pressure?

 

I put some HEET in the tank, and made the problem worse. I noticed the headers were glowing bright red, so I decided to pull the chip I had in and replace it with the stock 1989 camaro chip. The light went off and the car felt normal again. I found that I can't run high timing in the cold and with winter blend gas.

 

HEET = iso-propyl alcohol. that has a stoich AFR of 11.4:1, so the lean issue would certainly become worse.

normally, glowing headers would be a symptom of excessively retarded timing.... or at least, a really slow burning fuel(that didn't complete combustion before leaving the chamber/head).