Charging question on a 914-6 |
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Charging question on a 914-6 |
db9146 |
Jul 28 2018, 08:11 PM
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#1
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Senior Member Group: Members Posts: 953 Joined: 21-December 04 From: Atlanta, GA Member No.: 3,315 Region Association: None |
Well, I have made a temporary conversion of my -6, inserting a rebuilt 2.7S with ITBs, MS3, and distributorless ignition in place of the tired 2.0L. Before putting the engine in, I decided it best to install a new alternator along with a new engine/alternator wiring harness.
The alternator is for a 1965-1977 911 2.0-2.7 that uses an external VR. and here's the new wiring including a new ground strap to the engine case. The large red cable goes to the starter, the smaller red wire is D+, the black is DF, and brown is D-. I thought the problem might be the battery because of its age but when I checked the output of the charging system at the battery, there was none. I replaced some of the dash lights with LEDs but made sure not to replace the GEN warning light, which is not coming on despite the alternator not charging. Should I next pull the D+, DF, and D- plug and check for alternator output across DF and D+ momentarily? If there is output, what then? If not, what's next? |
db9146 |
Aug 14 2018, 08:09 PM
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#2
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Senior Member Group: Members Posts: 953 Joined: 21-December 04 From: Atlanta, GA Member No.: 3,315 Region Association: None |
If the battery voltage is over 12.6V when running then the battery is being charged. Spoke, why would you say that the battery is being charged at only 12.6V measured voltage at the battery with the engine running? I have always seen a figure between 13.6 and 14.4 as the output for a properly operating alternator. And yet, a couple weeks ago I took the car out for a drive in the evening and had the lights on. I stopped and had to get a jump to get the car started again. In talking with a friend this morning, he commented that if the old battery was so dead that it wouldn't start the car and then it ran fine the entire way home after a quick jump, that the alternator must be putting out some power just to run the engine and lights on the way home....a simple jump would not have provided the juice necessary for that. So honestly, I am coming back to your comment and wondering if the new battery I installed and checking of all of the grounds didn't fix the problem....and I'll just have to adjust to a new "normal" charging voltage. I really can't think of another way to test the alternator output if I can't perform the full field test for damaging the ECU. |
Spoke |
Aug 14 2018, 08:43 PM
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#3
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Jerry Group: Members Posts: 6,986 Joined: 29-October 04 From: Allentown, PA Member No.: 3,031 Region Association: None |
If the battery voltage is over 12.6V when running then the battery is being charged. Spoke, why would you say that the battery is being charged at only 12.6V measured voltage at the battery with the engine running? I have always seen a figure between 13.6 and 14.4 as the output for a properly operating alternator. The resting voltage of a battery is 12.6V. Anything higher than that indicates the battery is being charged. I just checked the battery voltage of my '86 930 when idling and revving to about 2500RPM and the battery voltage only increased to about 13.5V. I wasn't expecting the voltage to be that low but on the other hand I've never had an issue with starting or operating the car. Likewise about the 13.6-14.4V as the output being standard. My 914 does just under 14V at most all RPM. Not sure why the 930 is lower. It hasn't caused a no-start issue or running issue so I'll let it go for now. |
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