Does the Civic VX have a unique alternator?
 

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?

Hmm, I wonder if it's the
 

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.

Re: Hmm, I wonder if it's the
 

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.

The shop manual
 

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.

Re: The shop manual
 

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

So Randy, tell us about yourself :)

About me...
 

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.

learn something new...i
 

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

It's supposed to be through
 

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.

i'm sorry i dont
 

i'm sorry i dont understand...

You mentioned the two
 

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.