Im currently using the '8746 ecu. I run it open loop all the time. I have hiway mode set @ 50 mph and the timer @ 10 seconds. Will the ecu go into hiway mode in open loop, or will it have to be in closed loop?

 

For highway fuel it needs to be in closed loop. There are some other quals such as no MAP error's and some CCP stuff. This section of the code is in the EPROM, so it would be easy to bypass this if required.

Just be careful of which BCC you are using compared to the anlu hac. There are code differences in the '8746 ECM's. You may find that the addresses don't line up.

RBob.

 

Also, to add to Bob's post...you MUST have a good tune as well. The first time I ever invoked Highway Mode a number of years ago, I got WORST gas mileage initially because my "tune" was still off.

I only got my results with Highway Mode after I spent a great deal of time tuning my tables.

Now, I must admit that I am not as knowledgeable about your particular ECM/calibration, but Highway Mode can be accomplished in Open Loop by tuning to the particular AF Ratio/Spark Advance in your normal tables. You "Normal Tune" has HM built into the tables...much like you have P/E built into the tables.