having realized 125-129 readings under all normal driving conditions, and final tweaking of the MAT once i relocate it(waiting on harness connector) to achieve as close to 128 as possible.

It is my current understanding that highway mode fuel is basically as easy as getting to work as setting the constants and tables correct. this is my latest experiment and trying to learn more as i go. i believe i have everything set correctly to enable highway fuel at this time.

I am having a problem with highway spark advance i know thru glenns' posts on the subject that i do need to modify some of the source code to ensure a correct operation occurs(i.e. highway spark activates). I have the latest versions of the $8D 730 software and Tunercat itself and notice that there is still a min. rpm for highway spark advance undet the constants . This leads me to believe the only way to properly activate the HSM is to modify the source code as glenn has posted.

https://www.thirdgen.org/techbb2/sho...t=highway+mode

I am very bad with language/assemblers/dissemblers. I have seen others post, i believe it was prevost concerning the 747 ecm about modifying source code thru the PPII editing feature. I have been messing around with this and attempting to mod/view the source code but i dont have a clue as to what i am trying to do or even look at? I have a column labled hex and anther labeled ASCIII , i know these are languages but still lost as to exactly what i need to do to change it? I havent even begun to find out about the checksum afterwards and how to address that because as of yet im not sure what to modify in the first place or what i am looking at 100%.. ( I have the 730 hac but at a loss to coordinate that hac to what i see on the screen with PPII)

Just asking for someone to drop me a few kind works or a quickie explanation with an example or two so i can at least grasp what im looking at. Any "for dummies" level sites if u know of any would help me to im sure :-)
thanks guys
jeremy

 

While highway mode is neat in theory, I'm no longer sold on it.
To really make a difference means really lean and lots of timing.

It can seriously impact oil temps..
And that's directly related to engine life.

I've wound up going to 13.5 AFR at 28-32 timing for cruise mode, granted I have extremely small chambered heads, but the oem cal was using 42.

FWIW, remember there are no Free rides. ie what you save in gas may only be temporary, when offset against engine life..

 

I can see both sides of the issue grumpy so i wont be the one to debate with u there :-)

Just slowly trying to work my way thru the available options thru tunercat and hopefully modify some source code(still lost trying to use the PPII editor functions) that i know will work so i can start getting my feet wet and understanding what the ecm is doing and why gm did it that way and is it possible to make it better :-) Just getting a kick out of how much faster i can narrow down a chip for my car as i work out anothe rpiece of the puzzle and was doing this to try and play with the gas mileage to see if i could manage to increase it some. Not looking for the cure all wonder freebie(i can dream though) lol. Got to admit it is a lot of work and time but the results are pretty fascinating when u think about the garbage people pay money for.. and after the intitial investment, it is basically free to do in spare time hobby...

Have a few questions out there fpr people who have invoked highway fuel mode and/or highway spark as well

#1 I know my car has leaned out , can definitely tell by the pedal feel and the sogginess of it. If i manage to figure out how to enable highway spark mode it is my understanding that u can basically work around the sogginess with some additional timing?

#2 What is considered a normal o2 signal when running in highway fuel mode? Depending on what kpa vs rpm i am at i run from 40 mv to 90-100mv range and the o2 varies only by maybe 5-20mv tops when engaged and very infrequently.

#3 I have my fuel mode set for 60 seconds and have the delay set to 5 seconds? I know the converters need to see fuel once in awhile , are these safe times to use? I know my plugs all burn almost even on all 8 cyl and i pulled out the 2 easiest to check over once i got home and i dont have any trace detonation that is visible to my eyes. So anyone goign thru this feel free to comment as well and anyone who has worked it all the way thru please offer me your 10 cents.

I know its not a wonder cure all(nothing in life ever is:-( ) just trying to make reasonable use of everything contained in the 730 ecm one at a time
thanks
jeremy

 

So you found my old post. If you put all those changes via the Edit Function of the PPII software at the specific locations listed, it WILL work. Just make sure your re-read the bin with TunerCat first so it will reset the CheckSum. It is a LOT easier than you think. Give it a try, you can always go back to your original bin (provided you save it).

As for reliability, I've ran highway mode for over two years and over 60,000 miles with NO PROBLEMS. AND, this is on a motor with over 200,000 miles. Oil consumption the same, performance the same (actually better) and gas mileage greatly improved. I also know a number of others that have invoked Highway Mode and they are not finding any problems either - just better gas mileage. But Grumpy's warning should be heeded. I am "experimenting" and basically looking for a reason to rebuild my high mileage engine...but it just keeps going and going.

About the only thing I have noticed is that I need to clean the distributor cap. I clean it every three months to ensure I don't have any corrosion or carbon tracing. FYI, I've noticed this problem on a lot of other GM computer controlled V8s from the late 80s/early 90s - many bone stock. So I think it is more a function of the computerized HEI for V8s than Highway Mode itself. But I do recommend monitoring the distributor cap on a frequent basis.

Lastly, I ALWAYS keep my Highway Mode running, I never "cycle it". No adverse problems noticed and it still went through Air Care the last time I had to with no problems to the cats. I also envoke Highway Mode at 29 mph to get maximum gas mileage in the city too.

I have NEVER noticed any knock while in Higway Mode (with HMSA). I cannot say the same for when I drop out of Highway Mode and go into "normal mode" while climbing hills (we have LOTS of those where I live). And it is knock that is the killer of motors.

I did a LOT of testing and playing with the "transition" from Highway Mode to "normal mode" to minimize knock during the transition. I suggest you pay careful attention to this area as this is where you are most likely to encounter knock.

In fact, I had to do more work to minimize knock in the 70+kpa MAP area where Highway Mode disengaged AND the EGR started to turn-off. The EGR is critical to Highway Mode and controlling the EGR's operation at the higher MAP valuces (70+kpa) while switching from Highway Mode to "normal mode" is the most critical area to watch for to minimize engine killing knock.

 

When I tried the hiway spark mode it caused knock and advance was pulled. I gave up on it and went back to running without.

 

What ECM and what is your engine setup? Is your EGR functioning? And what was your AF Ratio for Highway Mode Fuel?

I found the functioning of the EGR and the leaness of the mixture (HMF) had a great affect on the amount of extra spark you can handle. I found 14.7:1 with an EGR at lower %DC is much more volatile than a leaner mixture with an EGR at 100%DC and produced more knock.

As I said above, I spent a lot of time in the "phasing out" in the 65-75 kpa range between Highway Mode Spark Advance, the Highway Fuel Mode and the EGR. The best way to "test" is on a long grade, trying various AF Ratios, Spark Advances and "cut-off" kpa values. This is one of the few times I wish I could have someone drive the car while I could fine tune "on-the-fly".

But when you are the "lone pilot", data capture works nice because I can review the information in far greater detail. I tried various "ranges" where I definitely notice knock occuring and another where it did not. They a few more test/burns (spare flash proms are nice here) to dial-it in.

 

Ive been temporarily sidetracked due to having to gut/part out my 87 442(ill miss her), work and being sick. Alos got a quirk going on in the formula and im trying to isolate it to a mechanical/electrical problem or just due to the weather(temp/hum.) changes. So i havent gotten a chance to play with it anymore. The only thing bugging me is whe i was goofing with PPII today and going to the edit function im still not quite sure at what im staring at and/or supposed to insert it at? What i get doesnt matcvh up to what i find when i go to the proper source in the hac....
thanks
jeremy

 

Im still bangin my head trying to work with the PP editor function.

this kinda stuff starts getting over my head
Any help or suggestions greatly appreciated
thanks
jeremy