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steffen707 · 04-03-2012, 01:32 AM

These are my original results, but it appears that the alternator was still charging just in low mode.

***UPDATE*** It is thought that this method just puts the alternator into a 12.5volt charging mode. I will try to test this further and report back with results. Don't be convinced yet that this is fool proof.

This is a half how to, half my results from testing this mod thread.

I have a 96 civic hatch and swapped a d15z1 into it. After reading about people disconnecting their alternator I decided to give it a try. if you go to pdftown you can download the service manual for your honda. From this site Timely Topics -- Your Vigor's Charging System The diagram they use is almost if not identical to my civic's diagram in the manual. I learned the alternator charging control wire which is green/white for 96 civic) and sends reference voltage from the alternator to the ecu. If the ecu grounds this wire, the alternator stops charging. Also, with this method the charging light indicator on the gauge cluster still works. You don't have to get out of the car and use a huge 100amp switch or relay on the charging wire like some people have done. You also don't have to run wires through the firewall. The alternator charging control wire for my car goes straight from the alternator to the ecu. i tested this with an ohm-meter. I simply cut the wire about a foot from the ecu and ran extensions from both of these ends to my switch mounted next to the steering wheel.

I used a dpdt switch from radio shack to connect the alternator charging control wire to the ecu and also to ground (they didn't have a spdt switch or I could have just used one of those). Now I can switch it to normal operation or "off via grounding" on the fly. (See http://en.wikipedia.org/wiki/Switch for info if you don't understand what dpdt/spdt switches are)

The switch works and the voltage drops right away. I’ll post pics in a day or so.

By the way if you use a similar switch, the middle part is “off” and nothing is connected. When you do this the alternator is still charging because it doesn’t see ground on that wire; however, if you read that whole page on the acuravigorclub website if says the ecu uses the ELD and the FR signal from the alternator along with other engine sensors to control the idle. Well when I set it to off it was still at 14.7volts at the battery; however, the idle speed dropped like 200 rpm. But when the wire was grounded it was 12.7volts but the idle was the same as if the wire was still connected to the the ecu. ODD....

Here are my results of a ½mile test with no electronics on except radio, 40mph steady speed, 54degrees outside, car weighs 2460 with driver and full tank, used mpguino and got car up to test speed and reset the mpguino trip odometer at the same sign and checked at the same sign.

73.8mpg - alternator on
74.8mpg - alternator off - 1.355% better

Same tests were run but this time with headlights on, A/C on full, rear defrost on.

56.1mpg - alternator on
63.45mpg - alternator off - 13.101% better

The first test was interesting because the difference in mpg was so small that a variation on my driving could have caused the difference, also I should have had my multi-meter connected to the battery so i could see if the alternator was even charging. I will probably re-test this sometime soon.

The 2nd test appears to corroborate the results of other people. Though I understand this was only a 1/2mile test it was more of a proof of concept for me and my car.

Next i tried some highway testing. Same limited electrical load and full electrical loads as before, 30minutes after first 2 tests. Car was brought up to 65mph on the speedometer (62.5 on mpguino) and i drove a 2.5mile course from A-B and then B-A and recorded results.

A trips (more downhill than B trips on same highway stretch)
56.6mpg - 62.7mph average - no load, alternator on
57.21mpg - 62.8mph average - no load, alternator off - 1.077% better
48.2mpg - 62.66mph average - with load, alternator on
50.14mpg - 62.90mph average - with load, alternator off - 4.024% better

B trips (lots of uphill, and my car is heavier and less aerodynamic than the civic VX from which the motor came from and thus it drops out of lean burn more easily than I would like, especially on hilly terrain at speed)
38.8mpg - 62.4mph average - no load, alternator on
39.7mpg - 62.5mph average - no load, alternator off - 2.319% better
38.3mpg - 62.5mph average - with load, alternator on
39.7mpg - 62.4mph average - with load, alternator off - 3.655% better

Here are some of my thoughts on the results.
1. With alternator off there was always a gain in mpg. I think this would carry over to full tank results as well.

2. with my vehicle the short run highway testing resulted in only a best of
4% better. I would like to do some long range highway tests to see if there is more of a gain or not.

3. The short run testing with load results was amazing, and with test results like this I ‘m curious if there was a fluke. More short run testing needs to be conducted to verify this. My car gets awesome gas mileage at 40-50mph, and I should re-conduct these tests without A/C, but instead just max blower on, as the A/C sucks a lot of power from the motor.

4. Though with no load my results at low speed were similar, I have to feel that over time and distance the battery will need to be recharged more (obviously) and when it needs this the alternator will kick in and then the MPG difference will be relevant again.

5. If a lot of my driving will be in town then this mod might be worth doing depending on charger/battery cost, cost of fuel, charging cost(120volt from house), and years for payback.

6. As for my initial highway results, it would not be worth the amount of effort or cost (for me). Though I agree that every little bit helps, the inconvenience of having to plug the car in to charge the battery, the cost of battery, the risk of being stranded due to user error, possible decrease in battery life, ect would not be worth a sub 5% increase to me.

7. I don’t pulse and glide or engine off coast, I don’t know by what amount that would change the percentages, but for these tests i was concentrating on staying at a steady mph, and less on feeling the gas pedal and trying to maintain MPG by slowing down up hills or accelerating in anticipation of hills like I normally do. A few 30-100 mile trips need to be conducted for me to determine if I should or shouldn’t persue this long term.

8. I would like to test the results with the alternator turned off against taking the alternator belt completely off to see how much actual drag there is. Lots of people say "its hardly any drag", but I havn't seen any actual back to back, ABA testing.

9. I did some in gear coast-downs and while getting 999999mpg doing so I switched from alternator on to off and you could feel the car slowing down faster with it on than off, so i know the switch was working. Also, i tried a few full throttle in 2nd gear tests getting up to highway speed and when you switched the alternator off it was like a subtle "vtec kicking in", you actually got a boost in acceleration. It was fun to flip it on and off several times on the same acceleration run to feel the car bog, then accelerate with the switch. By "bog" i mean you could feel the drag, it wasn't a ton, but was definitely noticeable.

Hopefully this information helps some guys. if you have any questions feel free to ask, I hope i can help.

This first picture is my mess of wiring for my obd1engine to obd2acar conversion.

This one is of me holding the green/white alternator control wire from the engine harness.

I taped the lead to the middle wire to test for continuity to the alternator plug.

Picture of the ohms while testing.

Picture of what pin on the alternator plug is the alternator control wire.

This picture is with the alternator switch in the up position to run as normal.

This is when you switch to the down position to ground the alternator control wire.

04-03-2012, 01:32 AM	#2 (permalink)
steffen707 Master EcoModder Join Date: Oct 2009 Location: Midwest Posts: 337 Thanks: 4 Thanked 37 Times in 21 Posts	These are my original results, but it appears that the alternator was still charging just in low mode. *UPDATE* It is thought that this method just puts the alternator into a 12.5volt charging mode. I will try to test this further and report back with results. Don't be convinced yet that this is fool proof. This is a half how to, half my results from testing this mod thread. I have a 96 civic hatch and swapped a d15z1 into it. After reading about people disconnecting their alternator I decided to give it a try. if you go to pdftown you can download the service manual for your honda. From this site Timely Topics -- Your Vigor's Charging System The diagram they use is almost if not identical to my civic's diagram in the manual. I learned the alternator charging control wire which is green/white for 96 civic) and sends reference voltage from the alternator to the ecu. If the ecu grounds this wire, the alternator stops charging. Also, with this method the charging light indicator on the gauge cluster still works. You don't have to get out of the car and use a huge 100amp switch or relay on the charging wire like some people have done. You also don't have to run wires through the firewall. The alternator charging control wire for my car goes straight from the alternator to the ecu. i tested this with an ohm-meter. I simply cut the wire about a foot from the ecu and ran extensions from both of these ends to my switch mounted next to the steering wheel. I used a dpdt switch from radio shack to connect the alternator charging control wire to the ecu and also to ground (they didn't have a spdt switch or I could have just used one of those). Now I can switch it to normal operation or "off via grounding" on the fly. (See http://en.wikipedia.org/wiki/Switch for info if you don't understand what dpdt/spdt switches are) The switch works and the voltage drops right away. I’ll post pics in a day or so. By the way if you use a similar switch, the middle part is “off” and nothing is connected. When you do this the alternator is still charging because it doesn’t see ground on that wire; however, if you read that whole page on the acuravigorclub website if says the ecu uses the ELD and the FR signal from the alternator along with other engine sensors to control the idle. Well when I set it to off it was still at 14.7volts at the battery; however, the idle speed dropped like 200 rpm. But when the wire was grounded it was 12.7volts but the idle was the same as if the wire was still connected to the the ecu. ODD.... Here are my results of a ½mile test with no electronics on except radio, 40mph steady speed, 54degrees outside, car weighs 2460 with driver and full tank, used mpguino and got car up to test speed and reset the mpguino trip odometer at the same sign and checked at the same sign. 73.8mpg - alternator on 74.8mpg - alternator off - 1.355% better Same tests were run but this time with headlights on, A/C on full, rear defrost on. 56.1mpg - alternator on 63.45mpg - alternator off - 13.101% better The first test was interesting because the difference in mpg was so small that a variation on my driving could have caused the difference, also I should have had my multi-meter connected to the battery so i could see if the alternator was even charging. I will probably re-test this sometime soon. The 2nd test appears to corroborate the results of other people. Though I understand this was only a 1/2mile test it was more of a proof of concept for me and my car. Next i tried some highway testing. Same limited electrical load and full electrical loads as before, 30minutes after first 2 tests. Car was brought up to 65mph on the speedometer (62.5 on mpguino) and i drove a 2.5mile course from A-B and then B-A and recorded results. A trips (more downhill than B trips on same highway stretch) 56.6mpg - 62.7mph average - no load, alternator on 57.21mpg - 62.8mph average - no load, alternator off - 1.077% better 48.2mpg - 62.66mph average - with load, alternator on 50.14mpg - 62.90mph average - with load, alternator off - 4.024% better B trips (lots of uphill, and my car is heavier and less aerodynamic than the civic VX from which the motor came from and thus it drops out of lean burn more easily than I would like, especially on hilly terrain at speed) 38.8mpg - 62.4mph average - no load, alternator on 39.7mpg - 62.5mph average - no load, alternator off - 2.319% better 38.3mpg - 62.5mph average - with load, alternator on 39.7mpg - 62.4mph average - with load, alternator off - 3.655% better Here are some of my thoughts on the results. 1. With alternator off there was always a gain in mpg. I think this would carry over to full tank results as well. 2. with my vehicle the short run highway testing resulted in only a best of 4% better. I would like to do some long range highway tests to see if there is more of a gain or not. 3. The short run testing with load results was amazing, and with test results like this I ‘m curious if there was a fluke. More short run testing needs to be conducted to verify this. My car gets awesome gas mileage at 40-50mph, and I should re-conduct these tests without A/C, but instead just max blower on, as the A/C sucks a lot of power from the motor. 4. Though with no load my results at low speed were similar, I have to feel that over time and distance the battery will need to be recharged more (obviously) and when it needs this the alternator will kick in and then the MPG difference will be relevant again. 5. If a lot of my driving will be in town then this mod might be worth doing depending on charger/battery cost, cost of fuel, charging cost(120volt from house), and years for payback. 6. As for my initial highway results, it would not be worth the amount of effort or cost (for me). Though I agree that every little bit helps, the inconvenience of having to plug the car in to charge the battery, the cost of battery, the risk of being stranded due to user error, possible decrease in battery life, ect would not be worth a sub 5% increase to me. 7. I don’t pulse and glide or engine off coast, I don’t know by what amount that would change the percentages, but for these tests i was concentrating on staying at a steady mph, and less on feeling the gas pedal and trying to maintain MPG by slowing down up hills or accelerating in anticipation of hills like I normally do. A few 30-100 mile trips need to be conducted for me to determine if I should or shouldn’t persue this long term. 8. I would like to test the results with the alternator turned off against taking the alternator belt completely off to see how much actual drag there is. Lots of people say "its hardly any drag", but I havn't seen any actual back to back, ABA testing. 9. I did some in gear coast-downs and while getting 999999mpg doing so I switched from alternator on to off and you could feel the car slowing down faster with it on than off, so i know the switch was working. Also, i tried a few full throttle in 2nd gear tests getting up to highway speed and when you switched the alternator off it was like a subtle "vtec kicking in", you actually got a boost in acceleration. It was fun to flip it on and off several times on the same acceleration run to feel the car bog, then accelerate with the switch. By "bog" i mean you could feel the drag, it wasn't a ton, but was definitely noticeable. Hopefully this information helps some guys. if you have any questions feel free to ask, I hope i can help. This first picture is my mess of wiring for my obd1engine to obd2acar conversion. This one is of me holding the green/white alternator control wire from the engine harness. I taped the lead to the middle wire to test for continuity to the alternator plug. Picture of the ohms while testing. Picture of what pin on the alternator plug is the alternator control wire. This picture is with the alternator switch in the up position to run as normal. This is when you switch to the down position to ground the alternator control wire. Last edited by steffen707; 04-09-2012 at 10:49 PM..