Why would the factory "Min. RPM for Highway spark be set to 3175, as it would never come on?
I read a few post about it being set to never come on, but why is this?
And also, why would Min vehicle speed for hi-way fuel be set at 255??
This is where you would conserve the most fuel cruising down the highway so why not use it for the factory?
Or am I just confused...
This is on a '92 TPI setup

 

Actually, I thought the "Minimum RPM" to enable Highway Mode Fule was something like 6,000+ rpm.

But, GM for reasons only truly known to them chose to disable Highway Mode - both Fuel and Spark Advance. I am aware of some fo the "rumours and theories", but they are just that "rumor and theories". The important thing to know is "GM disabled it". In fact, the Highway Mode Spark Advance is purposely disabled within the code itself so it will NEVER WORK on a SD car. You must modify the actual Source Code to make it work.

Do a search on "Highway Mode" and "Spark Advance". I made a post a while back on how to enable the Highway Mode Spark Advance by chaning the actual Hex Code. In fact, I make a change to the HMSA routine so that the "RPM" is a "Maximum" not a "Minimum" which makes FAR MORE SENSE.

I make my Highway Mode come on when I attain a few degrees below normal operating temp, minimum speed around 40 mph and max rpm around 3,000 rpm. I personally don't think any HM should be operation if you are over 3,000 rpm as you probably are "on it" and the HM routine could cause a problem with "too lean/too much Spark Advance" when you LEAST need it.

But do a search on "highway mode". I've written a lot on the subject, all waiting for people to read (if they care to search for it).

 

Thanks Glenn, I actually saw the rpm parm after I downloaded the .bin file from the chip for the first time and thought, "what the heck!" I did find numerous posts about how to change it, including your very good explaination of how to make the HS operational, just none really ever mentioned why it was set this way in the first place. Without it functional I don't see how anyone would ever get more than 15mpg or so.
I have several chips, including the AUJU(??) original and all the ones I have have this parm set to 3175, but to make sure it doesn't come on, 6k would be much safer for now I think.
Thanks