Battery Cable Upgrade

[Taylor95]

I performed what is known as the big three electrical upgrade. I replaced the block to ground cable, the alternator to battery cable, the battery to starter cable, and the battery to ground cable (yes that's more than three). I am not sure of the exact mechanisms behind the upgrade, but I have noticed an increase in my FE. In previous winters I would average an abysmal 15-16 mpg in my Jeep. The last two fill ups I got ~18.5 and 17.2 mpg. That is a definite improvement, especially when factoring in the less favorable driving conditions I face this winter. I would recommend this upgrade to anyone who still has their flimsy OE battery cables.

[jakobnev]

I doubt very much that the cable mod produced those results, there is just not enough power lost in the OEM-cables.

If for example you go from 16 to 18.5mpg at 100Km/h you are saving about 2l per hour. that's 19kW from the fuel, with 21% engine and 70% alternator efficiencies that would mean you had at least 2.8kW electrical losses in the wires.

The entire electrical load of a typical car is maybe a tenth of that.

[Taylor95]

The OE cables are pretty low quality in my Jeep. They were also about 22 years old, so they probably should have been replaced anyway. I don't know how important the grounding connections are but in my Jeep they were just flimsy wires. They were upgraded with the cables. And I suppose that I neglected to say that other mods I have done during the last 12 months include roof rack delete, synthetic oil in the front differential, and maybe my CAI. However, I believe that is negated by me doing significantly less highway driving. I see the mpg I am getting as quite an improvement and I attribute it to having new heavy duty battery cables. Even in the weeks preceding my project I was not getting very good mpg.

[redpoint5]

I attribute very little to your Big 3.

Jeeps are terrible on the highway, so that might actually be benefiting the fuel economy.

CAI won't help fuel economy in the least.

roof rack delete and synthetic oil should help a decent amount.

There's way too many variables going on here to make any proclamations of fuel efficiency improvements.

[Taylor95]

I know that how I am presenting this is not very scientific, however my fuel economy is definitely higher than the 6 weeks preceding my upgrade. I had all the mods I noted and the weather was just as cold. Others also report an improvement in mpg after doing the big three upgrade.
It makes sense to me as why this could be, because the spark plugs require electricity to ignite the air/fuel mixture in the combustion chamber. Something important that I should have noted in the first post is that I do not have the OE cap and wires. I have a mild performance set with my plugs gapped larger than stock.

[redpoint5]

I once had a pinched nerve due to a pulverized L5-S1. The chiropractor said he believed I could be rehabilitated if I saw him for "adjustments" 40 times over the course of 2 months.

Instead of doing that, I did nothing and my back got better over the course of 2 months. Had I completed the 40 adjustments, I would have attributed my healing to the so-called doctor.

My point is that there's too many variables at play to even suggest a result was achieved by a particular action.

It's possible it did improve fuel economy, and it was probably a worthwhile upgrade if the wiring was as poor as you say.

That said, it didn't give you a 12% fuel economy increase. It's not mathematically possible as Jakob alludes to.

If ignition performance were really poor, it would trigger a CEL.

Roof racks can make a huge difference though.

[Taylor95]

They weren't necessarily falling apart, but they weren't great either. There are lots of variables in play which are hard to measure. It is kind of hard to do ABA testing most of the time, so I try to deduct what I can from my fill ups. I suppose I should pay attention to confirmation bias. That being said, I think they did make a difference.

The roof racks did make a nice difference when I took them off. I think it was about ~1mpg.

That's fair to say it probably wasn't 12%. I think I do remember reading that larger spark plug gaps require more electricity to maintain. I did gap them larger because I've seen sources saying that a larger gap will cause better combustion, but it isn't very clear if I've seen an improvement in FE because of it.

[Stubby79]

He doesn't gain MPG from freeing up wasted electricity; he restores it from having better signals from his sensors, better spark and the like. Just cleaning the ground connections is usually enough, but replacing things would freshen them up as well.

Cleaning grounds is a normal practice in the geo metro community. It made one heck of a difference to my Miata, and my Ranger was doing all sorts of weird things before I cleaned it's grounds, like trying to die when I turned on the turn signals. Restoring power and MPG is just one reason to do it.

[redpoint5]

What model years were those vehicles Stubby? I'd expect a CEL on anything newer than 1996.

[Stubby79]

'95 metro, '91 miata, 2000 ranger.

Oddly, the ranger didn't throw a CEL. The older ones don't know any better.

Not sure you need to clean your grounds? check for a voltage difference between the alt case and the negative battery terminal, between either and the chassis, with the engine running. You want it as close to zero as reasonably possible.

Having a weak ground will affect the reference voltage going to your sensors. If it's bad enough, you start getting things grounding through each other, like my turn signals in the ranger, at which point weird things start happening when you turn on a load.