I don't think there is a DIY scanner out there for the 7747 ECM. So I'm tuning my van with the 02 sensor. Probably not the best way, but it's the only way right now.

If I lock the BLM (128 is best?) will the O2 sensor reading be more accurate, or more stable? I've read the other posts and page 2, but most of those are dealing with the scanner I do not have.

Also, if I do lock the BLM should I narrow the Int. as some have done?

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'92 Astro 350 TBI Edelbrock intake, MSD 6AL, 3.42's, 2.5" exhaust, Flowmaster 40 2 chamber, B&M 2nd stage shift kit, 255 60 R15 tires on AR-727's

 

You can be very successful tuning the part-throttle fuel tables using just a MAP sensor, RPM gauge, and O2 sensor. But you'll have to either lock both the BLM and INT values to 128, or disable closed loop operation. You don't want the ECM trying to adjust the mixture at all. With that accomplished, start tuning to get the O2 sensor to read 450mv. Take note that right around an AFR of 14.7:1, the O2 sensor will begin to oscillate, so you'll never really get a stable 450mv reading. So if you see the O2 swinging around 450mv at a particular load/rpm point, the mixture is set properly there.

Nick

 

Actually there is a DIY scan tool for the 7747. It requires some text file changes, but they are very easy to do with notepad.

http://www.techedge.com.au/vehicle/aldl160/aldl_sw.htm