Thread: The alt rewire mod actually DOES increase fuel mileage!!

I was a bit skeptical about the alternator rewire increasing fuel mileage, but it actually did! I drove home this weekend from college, and installed the new cable while I was there. I normally get 24-25 MPG driving back. This time I got 27, and that was averaging a speed between 80-85MPH. Also, take note that the drive is mostly through the Ozark Mountains (hilly).

Your results may vary. I've had one for a while and noticed no difference on anything. I'm sure it helps something and why it's still installed.

I'll tell you what Ive noticed over the last few years and I have now done this on three vehicles (getting ready to do a fourth on the Rodeo).

First, most people do not track their fuel mileage very well. Most of the time, and Im talking about 80%, people use guestimations about fuel economy. I see VERY few people that take the time to write down the trip odometer and main odometer readings and how much gas they pumped. I personally use my check card each time I gas up so that it has the cost, gallons and so on on the receipt print out and I write on it the odometer and trip odometer reading and I reset the trip odometer EVERY tank. I see very very few people take the time to record such information on their receipt or in some sort of fuel mileage log. Therefore they have little idea how far on a tank of gas they can go, or what kind of mileage they get.

Second, nearly everyone fills their tank up until the handle clicks off. And there is SO much variance in that it isnt even funny. I fill my tank up until it will take no more. As a result I have very accurate fuel mileage history.

Now, what I have done on my last three vehicles that has ALWAYS gained me mileage is upgraded the wiring. Starter, grounds, etc. My last vehicle gained me right at 2.5 mpg alone in doing that. With the Grand Prix I had a very long thread on ClubGP about the result of installing the voltage booster and the mileage I gained. I want to say it was close to 3 mpg if not a little more. I posted 4 tanks prior to installing the booster and 4 tanks after I believe it was.

So I have become a big proponent of upgrading the wiring and doing what you can to increase system voltage on a vehicle within reason. Obviously there is a point in which you can increase it too much and cause issues with electronics. My Grand Prix had a running voltage of about 14.5 volts or so, maybe a little closer to 15.

Let me give you a little math. Lets say your ignition coils are a 3100 to 1 ratio. That means for every turn on the coil on the primary side, the secondary has 3100 turns. Put 12 vdc to the primary, you get a little over 37000 volts out the secondary, to the plugs. Put 14 volts to the primary and you get 43000 or so volts out the secondary, which is dang near what after market coils put out.

Anyone want to guess what kind of effect that has?

Wire has resistance, maybe small amounts, but the larger the current output the more important that becomes and you can dang well bet that with something like the alternator and starter that resistance becomes important.

I just got mine today from Adam! Thanks Adam!!! I will be putting it on tomorrow. I hope it will fix my HID issue, or maybe give it a boost it needs to help the Igniters :P

I'll post back more I am sure The cable is excellent and well built!! Cudos to Adam!!!

I considered ordering the rewire kit online, but I didn't feel like waiting for it to be shipped... So, I went to Autozone and got a 2 gauge, 19 inch wire. It fits perfectly up from the alt, around the coolant overflow cap, and back down to the fuse box. I'm not sure if the larger wire will make a whole lot of difference in this case, but It definitely can't hurt any!

I am just curious if one running from the Negative on the Battery to a better ground on the car would help things along? I know they have those spider things you can put on your car and have like 6 or 8 new grounding points, but to me that is kinda overkill.

Just curious on people's thoughts on that one

Scotty, any way you could post that information on what exactly you did over here? I am interested.

Originally Posted by Zef_66

Scotty, any way you could post that information on what exactly you did over here? I am interested.

You mean on the voltage booster? If so it will have to wait until I get back home as I cant get to that site from work.

Originally Posted by archemedes

Scotty I have a program I enter all my stuff into and do the same as you fill it as full as possible, I can track exactly what my mileage is, and can tell if a tank was better or worse that way

What software are you using?

James, adding the larger ground wire as well ,will cover two of the "Big 3" for electrical upgrading. The third being a chassis to engine upgraded wire. I've seen people add one of the alt rewire wires between the vertical alternator mounting bolt to one of their strut tower bolts to acheive one of the Big 3 requirements.
The battery to chassis is easier with something like a yellow top Optima battery, where you can mount the ground to the top post.

"I fill my tank up until it will take no more. As a result I have very accurate fuel mileage history"........ I've always been told this a bad thing to do. I used to do it all the time and a friend of mine's husband said I shouldn't do it cuz it will cause problems.

Going off-topic a bit, but I have a question..... I've noticed when my gas hand get to the 1/4 mark it will start "floating" so to speak when accelerating. Is this normal? Should I have it looked at? I might have a quarter tank, but the gas hand will move up to almost 3/4's.

With regards to problems filing up til it cant take no more, I have never known it to cause problems and I have been doing it on so many vehicles its not even funny. Now, that said, I have noticed a time or two that it has resulted in a little sputtering from the current GP, and I believe that because of the EVAP system but Im not 100% certain of that. And the sputtering goes away after I have drove a couple miles.

With regards to your floating fuel indicator. I would expect a little movement, its not totally out of the question, but I have noticed it happening far less on the GP than any other vehicle I have drove before and Ive never noticed it on acceleration, but I havent been specifically looking for it either. And the swing you describe seems excessive at best.

Originally Posted by SyntheticShield

With regards to your floating fuel indicator. I would expect a little movement, its not totally out of the question, but I have noticed it happening far less on the GP than any other vehicle I have drove before and Ive never noticed it on acceleration, but I havent been specifically looking for it either. And the swing you describe seems excessive at best.

Its more of nussance to me more than anything. I know how far I can push it without totally running out of gas. I just didn't know if this was an issue that should be checked out by a mechanic or if its "normal" for the GP's. Thanks!

Originally Posted by IndeedSS

Your results may very. I've had one for a while and noticed no difference on anything. I'm sure it helps something and why it's still installed.

Yea same here installed mine about a month ago and and voltage booster and i haven't noticed any difference eaither, but like you said results may very.

I have done the alternator "rewire" and later the volt booster (stage 1). I can say for sure that my headlights were increasingly brighter after each of them. Some have said there were some improvement to the idle and tranny shifting. I think I noticed the same thing. It was minor enough that it could be placebo, but in the end I was happy with it. Peace of mind if nothing else. If you are resourceful you can do both on your own for cheap, but it was just easier for me to buy them pre-made.

I think the Big 3 is a very good thing. However, I'm wondering if the noticable benefits or perceived lack of, may depend on the age or condition of the system beforehand and how much the system is already being pushed to it's limits.

Okay, if that is true then, then it would go to show that the rewire has some effect. If the system is aging and stressed or pushed to the limit and this simple mod relieves some of that and is noticeable by way of brighter lighting, better shifting (I noticed this on my last vehicle I did this to, not so much on the GP, Rodeo is manual tranny) then that would prove that it is changing for the better the electrical system.

So therefore, why would it be such a stretch to believe that this could help mileage? That said, if you want proof it helps, then go out to your car, reduce the system voltage to lets say 11.5 volts or even 11.0 volts and drive for a week or two and report back on your fuel economy.

I would have never ever believed it in a million years myself had I not done it on the number of vehicles I have and seen the results I have.

I believe it was Zef that asked about my post over on Clubgp and the voltage booster.

Here is the mileage I got for the 5 tanks of gas BEFORE the voltage booster:

06.02.2006
Miles on tank: 384.4
Gallons to fill up: 17.294
Mileage: 22.23 mpg

06.04.2006
Miles on tank: 150.6
Gallons to fill up: 7.622
Mileage: 19.76
(a great deal more city and sprited driving on this weekend)
Among that spirited driving was a 36 mile trip averaging well into the 90 mph range with several very long stretches 110+. I had gotten a call that my step-son had been taken to the hospital and was having seizures.

06.09.2006
Miles On Tank: 361.1
Gallons to fill up: 15.0
Mileage: 24.07 mpg

06.16.2006
Miles On Tank: 408.9
Gallons to fill up: 17.70
Mileage: 23.10 mpg

06.19.2006
Miles On Tank: 217.8
Gallons to fill up: 9.391
Mileage: 23.19 mpg



Here are the tanks AFTER the voltage booster was installed:

06.24.2006
Miles On Tank: 446.0
Gallons to fill up: 17.00
Mileage: 26.24 mpg
(First tank with the voltage booster installed)

06.30.2006
Miles on Tank: 410.8
Gallons to fill up: 14.80
Mileage: 27.75 mpg
(Second tank with the voltage booster installed)

07.10.2006
Miles on Tank: 294.7
Gallons to fill up: 11.92
Mileage: 24.7 mpg

07.16.2006
Miles on Tank: 401.3
Gallons to fill up: 15.79
Mileage: 25.4 mpg

07.22.2006
Miles on Tank: 463.3
Gallons to fill up: 17.313
Mileage: 26.7


Here is the text of my final update:

I thought I would post up one final update on this and then let it go where it may. My last update was on June 30th and I think I had mentioned then that because of the holiday my mileage would be lower because I was off for four days and would be doing nothing but city driving. I had some fun with some spirited driving from stop lights but no full WOT runs that I can recall. Below will be the fill ups from the 4th of July period to current. Last fill up was on June 30th which I posted already. Next fill up came on July 10th. I had enough fuel left to get back and forth after filling up on June 30th since I had the four days off and only had to go to and from work three days which accounts for about 200 miles or so of the July 10th fill up. Hope that all makes sense.

I cant explain why, as a result of all the city driving over the 4th of July holiday that it took a while for the mileage to recover. I dont think my driving habits had changed any.

I posted my 5 previous tanks mileage before doing the voltage booster. I now have 5 full tanks with the voltage booster.

Overall mileage before: 22.47
Overall mileage after: 26.15

Change: +3.68 mpg




Okay, now to add this. Keep in mind that the above tanks represent about 65% highway, 35% city. Maybe 70/30 it just depends on how much I get out an about on the weekend. Prior to the tranny trouble I had touched on 34 mpg on the highway, but was pretty consistently about 32 mpg.

When I resurrect this sucker, if all goes according to plan, I plan on having even higher fuel economy. Anway, there is the information.

As I said, I noticed no difference but did the alt rewire and stage 1 V boost at the same time. No change in gas milage and what I was really after, the dimming of the headlights when operating the power windows, no visually detectable difference either.

The whole point wasn't whether someones else gained MPG by adding a power wire, but that your results may vary.