EOC ~ only useful at low speeds

[P-hack]

Originally Posted by johnlvs2run

The battery use is much higher.

Yah, but power demands should be lower since you aren't running injectors or spinning alternators and stuff. Though there is probably a break-even point for getting everything stopped and started rotating again. I do wonder if cutting an injector is the best approach though, the ECU is bound to see a fault and may go open loop after restarting, whereas if you switch off the rpm signals to the ecu, it may simply "think" the car is stopped (and you don't need much of a switch to break a signal). How you kill it might be a factor. My honda gets a CEL when I break an injector lead.

[PaleMelanesian]

I never saw such a problem with my 96. I was keying off momentarily to kill it. Do you have an injector or ignition kill instead? Try using the key for a while and see if you have different results. That battery usage seems more than excessive. I would see a spike in power consumption when I key on, as the fuel pump primes, but then it drops back down.

[j12piprius]

Originally Posted by PaleMelanesian

I never saw such a problem with my 96. I was keying off momentarily to kill it. Do you have an injector or ignition kill instead? Try using the key for a while and see if you have different results. That battery usage seems more than excessive. I would see a spike in power consumption when I key on, as the fuel pump primes, but then it drops back down.

I'm using a main relay fuel injector switch. Turning the ignition (not the engine) off and on 10 times, with 3+ second pauses, only drops the battery by .02 volts total. The key must be turning the injectors on and off, and there is the same thumping sound, so I wonder what the difference is.

[j12piprius]

The PGM-F1 main relay ground controls the fuel injectors, fuel pump, o2 sensors, alternator, vehicle speed sensor, and maybe the PCM, one or more of which must be causing the drain.

I've not found a fuel injector fuse, so I'm going to splice into the fuel injector wire, before it gets to the PGM-F1 main relay.

[oldtamiyaphile]

I would tend to agree with John's hypothesis. The more you EOC the more voltage you loose, and that energy then has to come from the alternator. It takes around 7hp for a small car to cruise and an 80A alternator can output 1.5hp, if the alternator has a lot to do you can see that can be a big hit to economy.

When UFI got a battery twice as big as stock, my MPG went up by as much as 15%, I charge it at home and the alt has nothing to do for at least the first 140 miles.

If you've got a lightweight car with poor aero, I've found EOC to be ineffective.

If you've got a 2 ton van EOC works at freeway speeds. I've adding a solar panel to my 1.5 tonne van roof next week to offset the EOC battery drain. Personally, I expect significant gains. Right now I often EOnC out of kindness to the battery when the voltage is reading a bit low already.

[PaleMelanesian]

Originally Posted by oldtamiyaphile

I would tend to agree with John's hypothesis. The more you EOC the more voltage you loose, and that energy then has to come from the alternator. It takes around 7hp for a small car to cruise and an 80A alternator can output 1.5hp, if the alternator has a lot to do you can see that can be a big hit to economy.

When UFI got a battery twice as big as stock, my MPG went up by as much as 15%, I charge it at home and the alt has nothing to do for at least the first 140 miles.

Yes. I believe it. I have to do a lot of voltage management to keep things healthy, including overnight charging - daily in winter with headlights but less in summer.

If you've got a lightweight car with poor aero, I've found EOC to be ineffective.

I disagree completely.

[j12piprius]

Originally Posted by oldtamiyaphile

When UFI got a battery twice as big as stock, my MPG went up by as much as 15%, I charge it at home and the alt has nothing to do for at least the first 140 miles.

I've adding a solar panel to my 1.5 tonne van roof next week to offset the EOC battery drain.

Great ideas! I'll keep those mods in mind. Thanks for the feedback.

[oldtamiyaphile]

Originally Posted by PaleMelanesian

I disagree completely.

I should have added 'at freeway speeds'. Keep in mind your Fit is both heavy and aerodynamic compared to my Fiat 500. Even with my Renault Kangoo (Van) which only weighs 1270kg for a pretty big vehicle (0.33cd) EOC is worthwhile.

I'm right into EOC but there are some cars for which it doesn't work.

[PaleMelanesian]

Actually, no. Our cars are about as close a match as you can find from different makers. According to Edmunds.com, your Fiat is just barely lighter and about equally aerodynamic. (2363 lb vs 2490, cd 0.33 vs my 0.34). They're both tallish hatchbacks, with the drag that comes with that basic form. The Fit is also slightly bigger, making the cdA worse (66.7 in wide x 60 in high vs your 64.1 wide x 59.8 high).

It could be that your engine management runs rich for a while after a restart or something like that, making the shorter eoc cycle at highway speed less beneficial.

What is your highway gear ratio like? I'm all the way up at 2850 rpm @ 60 mph, so anything I can do to minimize that, like p&g, is a huge benefit. A lower cruising gear would close the gap and reduce the possible gains.

[oldtamiyaphile]

Edmonds is wrong on the CD, it's actually 0.367 and mine is European spec so only weighs a fraction over 2000lbs (and mine's been lightened). I also have the bigger 'Abarth' rear spoiler and 16" wheels so I wouldn't be surprised if my actual CD was around 0.38.

The engine has factory stop start so stays closed loop on restart. It spins at about the same revs as your Fit at 60mph but it's a 2cyl without throttle plate so at least the pumping losses are low, it's also got Fiat's fancy Mulitair valvetrain.

It's a turbo car and EOC is a bad idea for it anyway, but EOnC has shown significantly worse results than DWL (at 875cc it burns very little at idle). Aggressive EOC might brake even with DWL but wouldn't be worth the bother. It takes absolutely forever to get back up so speed an no time at all to scrub it.