I've heard it said before (by Glenn on the TPI board) and need to confirm to make fact.

Q: Will invoking highway mode enable me to save enough money on gas to pay for the prom burning equipment?

I need to know since my dad MIGHT consider investing in the equipment if he can save on gas (seeing how I get 16.5 mpg now).

Also, he has a question:

Q: Will invoking highway mode run my engine lean enough to cause a problem? Is it safe? Will I shorten my engine life?

Thanks guys, I hope to be burning my own chips within the month.

------------------
~3.1EyeCandy~
"The Car that started my craze"

'92 Firebird 3.1 (A car sold)

My new baby: '87 flame red GTA 350 w'auto, ported and polished plenum, custom cold-air intake w/K&N, 180* thermostat, Hooker SuperComp Exhaust, Splitfire plugs, Hypertech Airfoil,
Carmine interior with pioneer all around
My Cars

jonathan_badgett@yahoo.com

 

Depends on your current combination. You might get better mileage, but like anything else, you *might* get in there and worsen things.

Again, you can goof things up and have problems.

If you constantly heavy into the throttle 16 MPG might be the best you'll get.

Would be nice to promise better, but that would be lieing.

Good chance that done right, you'd get better mileage. Just about guaranteed to learn something thou, and that is what makes life interesting.

 

With the new fuel pump in (a whopping 400 bucks dropped on that one) and gas prices soaring, I'm GRANNY on that throttle.

From what I've read from the archives and searches, it seems that I definitely need to tune the chip for my car BEFORE invoking highway mode. No problem. My current combo is a stock 87 GTA (I'm the one who posted before about getting chip burnt for my car and now I really want to burn my own) with no internal engine mods.

My question still remains (though thanks for responding Grumpy), if I properly tune the chip first, then invoke highway mode, will I hurt my engine?

I guess its a stupid question, seeing as how I can change all aspects of highway mode. What I'm really trying to figure out is if there is anyone out there with a stock car running a tuned chip with highway mode. And what kind of mpg are they getting from the car.

Once again, thanks.

 

IMO 16.5 highway mpg on a stock 87 GTA is way off course. My stock L69 carbed IROC went 25 mpg at 65mph. Hell, my C2500 gets 17mpg (mixed driving) and it weighs up around 4600lbs.

I'd suggest getting the stock components up to par before tweaking the PROM. You should make atleast 22 mpg. My first guess is leaking injectors. Seemed to be a problem around 87.

[This message has been edited by Brent (edited August 13, 2001).]

 

If the 16.5 mpgs is a "combined" city/highway mileage, that is a little on the low side but basically "normal" for a stock setup. City driving by itself is probably the hardest when it comes to gas mileage.

My original gas mileage (before modifying the eprom) was 22-24 mpgs for "pure highway" and around 14-16 mpgs for basically "pure city", but no "stop n' go" rush hour traffic (where you can get 0 mpgs).

Invoking Highway Mode allowed me to increase BOTH highway and city mileage. I invoke my "highway mode" at 31 mph, so I also get the benefit in city driving along with highway driving.

I tried various Air Flow ratios and I have gotten as high as 30 US mpgs with 17.4:1, but I also noticed a little "surging" on flat roads/low load situations due to the very low AF ratio and very high spark advance. I now use around 16.4 and lowerd the spark advance a few degrees and this cured the "surging" sensation. I now get around 28 mpgs on highway driving of 65 mph in mountain driving (and still passing slow semi-trailers on occasion). So it isn't exactly "granny driving" either.

I haven't checked my "pure city" driving as I now live in a smaller community and there isn't "much of city" where I live. But there has been a dramatic increase in my city mileage (based on how much it decreases my overall gas mileage). I attribute this to invoking Highway Mode at 31 mph.

Base on how I drive, YES, the savings in gasoline alone has paid for my eprom buring equipment AND it will continue to save me money. Also, I have a LOT MORE peformance than I had before and a lot of fun doing it.

As for your current gas mileage; when was the last time your O2 sensor was replaced? If your car is in "perfect tune" with new plugs, wires, cap, etc and your mileage is still low (or lower than normal), I would suspect your O2 sensor may be a little "weak". It has been my experience that when a vehicle starts to get "poorer and poorer" gas mileage, even after a tune that usually it turns out to be a "weak" O2 sensor where it still operates well enough to not trigger a SES code, but not strong enough to give accurate readings.

Have you checked your plugs the last time you changed them? In spite of my bad back, I ALWAYS insist on doing my own spark plugs just because they (spark plugs) are your only "eye" to what is happening inside your engine. It can tell you if you are running basically rich (or lean) if all the plugs are generally the same color. Or, let you know if one (or a few) cylinders are "weak".

With Highway Mode and my various prom tuning, my plugs are never black anymore. They are a nice tan color, even after 6 months of driving with a nice "balance" between all cylinders. Also, I find a DMM useful for checking plug wires. I use MSD Superconductor wires and found that after 18 months of useage, half of my plug wires were between 90-150 ohms (basically as brand new, depening on length), 2 were around 1,500 ohms (weak and equivalent to stock GM wires) and 2 were over 20,000 ohms (bad and amazed it still allowed the spark plug to fire).

 

Does my mileage seem that low? I was pushing 19 mpg before the new pump...alas, I was also running 36 psi. lol, that was my starting problem. I'm still in school, so sitting in a cramped parking lot for about 20 minutes a day with the car idling has something to do with the bad mileage, but before school started, I was pushing 17. I'm up to date on the plugs, cap, rotor...but haven't replaced the o2 yet. My weak cylinder is #8 *whose isn't?* and even then it was a mint plug with fine dust on it when it was taken out. Thanks for the responses, though doubting my injectors doesn't make my wallet feel any heavier.

"I would suspect your O2 sensor"

I'll change it this weekend, it does make sense. Before when I had my starting problem, it took ether to start and always blew smoke out the pipes. That probably coated my o2 sensor. Thanks guys.

------------------
~3.1EyeCandy~
"The Car that started my craze"

'92 Firebird 3.1 (A car sold)

My new baby: '87 flame red GTA 350 w'auto, ported and polished plenum, custom cold-air intake w/K&N, 180* thermostat, Hooker SuperComp Exhaust, Splitfire plugs, Hypertech Airfoil,
Carmine interior with pioneer all around
My Cars

jonathan_badgett@yahoo.com

 

When you are idling your engine, you are getting 0 mpgs. If I am going to be stuck where it appears that I may be idling more than a couple minutes, I shut my engine off. An engine will burn more gas idling in 2 minutes than it will to restart, especially FI as you never put your foot on the gas peddle when starting.

FYI, even when my car was "bone stock", I've never gotten mileage worst than 20 mpgs on the highway EXCEPT if I was travelling at average speeds well over 80 mph.

As for the question of "will Highway Mode harm my engine"? As long as you don't go too crazy with the AF ratio (above 18:1) and not too crazy with the spark advance you should have no problems. You will probably find more "driveability issues" with AF ratios above 18:1 as I have noticed that my engine starts to "surge/buck" when the AF ratio gets too low with a low load. This is caused because the Injector Pulse width starts to get very short (around 1.0) which is around the minimum pulse width.

Also, the O2 sensor is not designed to be accurate at this level of AF ratio. When I tried using 18:1, I found my O2 mVs drop to single digit values, the engine would "surge" and it didn't really make that much of a difference in the fuel economy...not enough to make me want to drive @ 18:1 based on the driveability issues I noted.

One thing to consider IF you decide to run Highway Mode @ ratios between 16:1 - 17:1, you MAY wish to consider using spark plugs of one range colder. I actually went to colder plugs for WOT reasons, but I am noticing that the plugs have a "nicer color" than the stock heat range. I will give a "long term" review in a few months on the use of colder plugs.

However, if you do a lot of "city driving" you may wish to keep the stock plugs, or invoke Highway Mode sooner (31 mph) to avoid fouling.

 

Thanks Glenn. I'm busy trying to find out why my mileage is so bad right now. (I just put the car on a below 2000 rpm diet) and am hoping its my highschool foot that's the culprit. It gets annoying when one of my friends with a 92 tbi 305 w/nos gets 24 mpg and frequently pushes his car to/past the redline and recently was clocked at 150 mph. I suspect the o2 sensor, but if that fails, I may be saving for new injectors instead of a prom burning setup. Thanks for all the suggestions and now I know, highway mode is safe as long as you don't push it too far.

 

What is the ballpark for timing that you guys are running during highway mode?