Does the Civic VX have a unique alternator?

[Matt Timion]

I recently read something online that claimed that the Civic VX has a special alternator.

According to this claim the VX only recharges the battery when the car is decelerating.

Does anyone know if this is true? How much MPG benefit do you think such an alternator would produce?

[DaX]

Hmm, I wonder if it's the alternator or if it's part of the circuitry connected to the alternator.

The honda parts website shows no difference in part number for VX vs. DX, or for Cal vs. Non-Cal emissions.

I know I have used my VX alternator on another one of my cars at some point, so I know it will work with other ECUs/engines.

[Matt Timion]

Originally Posted by DaX

Hmm, I wonder if it's the alternator or if it's part of the circuitry connected to the alternator.

The honda parts website shows no difference in part number for VX vs. DX, or for Cal vs. Non-Cal emissions.

I know I have used my VX alternator on another one of my cars at some point, so I know it will work with other ECUs/engines.

you're right, it could be the ECU. Then again, I'm unsure how smart it is to do this type of thing. If it ONLY charges on deceleration, the battery would die on a road trip if you were using the radio. it might just not charge whild under acceleration, assuming this is true at all.

[Randy]

The 94 shop manual doesn't list any difference between the VX and other trim levels. However it does say the ECU tells the alternator to switch from 14.5 to 12.5v if you have the starter switch on or all the following are true:

Load below 10A
Speed below 40 MPH
Engine speed below 3600 RPM
Coolant temp above 140 F
A/C off
Intake air temp above 65 F
Brake switch off
Fuel cut-off not active

Even if it did this more often, it wouldn't be that big of a deal: 12.5v won't drain the battery. It just wouldn't recharge it.

[Matt Timion]

Originally Posted by Randy

The 94 shop manual doesn't list any difference between the VX and other trim levels. However it does say the ECU tells the alternator to switch from 14.5 to 12.5v if you have the starter switch on or all the following are true:

Load below 10A
Speed below 40 MPH
Engine speed below 3600 RPM
Coolant temp above 140 F
A/C off
Intake air temp above 65 F
Brake switch off
Fuel cut-off not active

Even if it did this more often, it wouldn't be that big of a deal: 12.5v won't drain the battery. It just wouldn't recharge it.

This is very cool information. Looks like honda didn't cut any corners with the VX.

So Randy, tell us about yourself

[Randy]

I've got a 94 Civic EX. I get a little above highway rating with a few extra psi in the tires and driving carefully. This summer looks to be a bit painful, so I'd like to try and wring a little more mileage out of it. I also have a 79 F250 for stuff that doesn't fit in the Civic. I have to phone Saudi Arabia before firing it up.

I'll try and do some more investigating on the alternator. There's only 1 ECU control wire, so it may be simple to override the computer.

[molecule]

learn something new...i never owned my vx manual...
i still find it hard to believe...
as the alternator doesn't have any special connectors or anything...
A16 & D9 ... standard pinouts for the alt on all civic models

though i do see an "economy driving indicator control" D18
and as i stated in another thread i've never seen an econo-light in any vx on the dash...
maybe this alternator control is through the ELD electrical load detector circuit...
thats my best guess...i'll try digging through the wiring diagrams some more...
though ELD is not standard on all the civics...
i think all canadian models are lacking
my canadien VX did not have ELD
whether or not it had this 12V mode...i dont know...first i heard of it...
i have heard of the a/c clutch which engages at specific times to make the engine more efficient...
the vx a/c compressor is definately unique

nope D18 is just the shift light
D10 would be the ELD...though as stated...not on all models

[Randy]

It's supposed to be through the C connection (A16). FR (D9) is supposed to be field level into the ECU. Almost all alternators have the ignition and alt light connections, so those two are unusual.

[molecule]

i'm sorry i dont understand...

[Randy]

You mentioned the two connections from the alternator to the ECU in your post. One is called "C" on the alternator, and connects to pin A16 on the ECU. The other is called "FR" on the alternator, and connects to pin D9. I think they stand for 'Control' and 'Field'.

There are two more connections to the alternator on its green plug: "IG" gets power when the ignition is on (to jump-start the field), "L" connects to the alternator light. This is in addition to the heavy Battery connection. These connections are industry-standard for alternators, but C and FR aren't.

Anyway, I checked it out on my EX. You just ground C to switch to the lower voltage. It draws about 1 mA, so no resistor needed. I measured the current into the battery, and it looks like it does discharge it a little at the lower voltage. Still it's not bad... about 3A at most, and it should zero out well before the battery discharges. This is with an Optima, so it might not be so bad with a normal flooded. You couldn't just always stay at 12.5v, but you could spend 90% of your time there.

[molecule]

so then this optimization isn't just for the vx...
they all use it...
they wouldn't run the wire for nothing on all the other models...
at least i dont think they would...
and if thats the case...i do nothing but sit idly by and save...
or do you think i need to "do" something to enable the feature

[SVOboy]

The ran all the vtec wires and such in all the 92 civics, regardless of vtec, as well as in all the del sols up until the 96 model, I believe. So they might've just put it there.

[Randy]

I think it's in all the civics, at least 92-95. However if you look at the list of things needed before it turns on, it wouldn't be on very often. The 10A draw for example means that nothing other than the engine is on.

You could install a switch to ground out the C wire (no need to disconnect it from the ECU), then leave it in low-voltage mode most of the time. I think a few minutes per trip would be enough to top off the battery. Things use about 30% less power at 12.5v.

[molecule]

yeah seems reasonable...as long as memory would serve me to throw the switch...
lol

svo
vtec was pre-wired only in all the 92 civics
after that...only in cars that were equipped w/ vtec engines

[SVOboy]

svo
vtec was pre-wired only in all the 92 civics
after that...only in cars that were equipped w/ vtec engines

That's what I just said.

[Ryland]

what page of what repair book gives this information? I've looked at both my factory service cd-rom manual (a pain in the *** to read, i like books), and hanes manual, and haven't found anything.

[Randy]

Originally Posted by Ryland

what page of what repair book gives this information? I've looked at both my factory service cd-rom manual (a pain in the *** to read, i like books), and hanes manual, and haven't found anything.

In the 1994 Factory Service Manual, first edition it's the back where they take apart the alternator. Page 23-128 and 129. I got the manual from Helminc.com, though I bet your cd-rom is the same thing.

[MetroMPG]

how did i miss this thread. this site is getting too busy!

i recently heard from a crx hf owner that this was a feature on his car way back in the day (it was an 85 i think). field weakening.

i still want to test my car with the alternator completely disconnected (un belted) and see if it makes a measurable mpg difference.

but i need to keep the water pump going (it's all on the same belt) and not sure what kind of smaller belt to jury rig in there, since it won't be adjustable/tightenable. the panty hose trick? bungee cord?

[95metro]

Originally Posted by MetroMPG

but i need to keep the water pump going (it's all on the same belt) and not sure what kind of smaller belt to jury rig in there, since it won't be adjustable/tightenable. the panty hose trick? bungee cord?

Just get one of those adjustable emergency belts from CT. Should work well enough for a few tests.

[MetroMPG]

cool - i didn't know there was such a thing. i'll have to check that out.

(and what was that about not being helpful?)

[95metro]

Originally Posted by MetroMPG

cool - i didn't know there was such a thing. i'll have to check that out.

(and what was that about not being helpful?)

I guess I have my moments - but don't thank me yet, they ain't as cheap as I thought...

http://www.safetycentral.com/fanbelrepkit.html

...as an alternative just measure the belt size you need and see if you can find a belt from pre-serpentine days that will fit.

[MetroMPG]

as an alternative just measure the belt size you need and see if you can find a belt from pre-serpentine days that will fit.

how about an old inner tube, cut to the width of the belt, and stapled together to make a tight band?

i just tried it. my friday after supper project!

i took the OEM belt off, jury rigged the water pump inner tube band, and drove my city "test loop".

some interesting observations:

- the DRLs do not switch on when the alternator isn't pumping out the amps (clever! thanks, suzuki engineers!)

- the engine seemed to run smoother at low rpm, suggesting i removed a noticeable load. it also clutch started smoother (these observations subject to placebo effect & experimenter bias!)

- i got my best mpg ever. 86.0 mpg (US) indicated on the scangauge. that's not "proof" of anything - also subject to experimenter bias. i need to do back-to-back testing using the better methodology on my flat, straight test course.

- surprisingly, the stapled "rubber band" belt stayed together and on the pulleys. i don't think it'll last very long though.

[95metro]

Originally Posted by MetroMPG

how about an old inner tube, cut to the width of the belt, and stapled together to make a tight band?

Well, that's certainly the Jack Benny approach to the problem...