I know that these will ecms are pretty much a plug a play swap except for the differences in proms. I have a 350 tbi with the 7747 but been thinking about swapping to the 8746 to get highmode to see if I can get some better mileage? Or does the 7747 have highway mode that is disabled, I am not good at reading code. Is this a worth while swap to do or am I wasting time? I did a search and did not see anybody having tried this.

 

Meh... Highway mode didnt always seem to give me noticably better milage. I sure the tune plays some part. Youd be better off spending the money on prom burning stuff so you can do some tuning if you want to try for better milage all around.

 

I haven't played with it but all of the BCC's I have looked at for my 7747's show the highway mode.
Guess it could be a mistake in the ECU file.
I mostly use the ASDU9567.

 

To swap in the '8746 only need to add an IAT sensor. The '8746 is a more refined ECM designed for car use, as opposed to truck use.

There is a lean cruise highway mode patch for the '747. That is what is being seen in the '747 ECU files. Unless the ECU entries are for highway SA, that is stock.

RBob.

 

I do have prom burning stuff but I thought highway mode might give me a little bit more. But it kinda sounds like it is not worth it. I'll just tweak what I have some more and live with it.

 

I think it may eb able to help, but your tune has to be good to start off with. I used it and I didnt notice much difference over just running closed loop. Im sure if everything had been dead on I may have had some tangable increase in economy.

 

my 7747 shows on WB as low as 30/1 on highway deacelleration. cruise/enleanment( i logged this am for heck of it) i wanna say is 17/1 but as soon as a load on engine(small incline) AE comes on and puts AF to about 14/1. so it appears i do have highway mode.