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, 07:38 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 |
LarryM,
Thanks for the great additional info!!! Saved it for reference. Tonight I checked and: - I have a 12V 2W Osram buld in the GEN socket - it lights when I turn the ignition on - it goes out a moment or two after the engine starts up - I get 12.5V at the dash light - 12.5V at the D+ female on the circuit board that the VR plugs into - 12.5V at the D+ male spade on the circuit board that the plug from the Alt. connects to - and 12.5 at the DF male spade on the circuit board that the plug from the Alt. connects to. LarryM, you mentioned that the issue may be upstream in the wiring at the dash or ignition switch. If I'm getting 12V at the GEN bulb and D+ on the circuit board, wouldn't that indicate that the wiring between the circuit board, dash, and ignition switch is okay? I understand that the next step is to try to measure the full alternator output by jumping DF to D+ but I really don't want to do this because the new engine is running individual throttle-bodies and MS3x. (CAUTION: Voltage is unregulated during this test and could damage sensitive electronics. {Balmar Alternator - Regulator Troubleshooting}). I think that means that I could kill my ECU. It seems I really need to find another way to test the alternator. NOTE: Before trying to perform the full field testing, I read that one common way to test modern alternators is to test for a magnetic field with a screwdriver once the switch is turned to the "on" position. However, I don't this will work on a Porsche -6 since it relies on the bulb to provide the resistance to "tickle" the alternator into charging. (Man I don't want to drop the engine for this....) |
larryM |
Aug 15 2018, 09:22 PM
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#3
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emoze Group: Members Posts: 891 Joined: 1-January 03 From: mid- California Member No.: 65 Region Association: Northern California |
If I'm getting 12V at the GEN bulb and D+ on the circuit board, wouldn't that indicate that the wiring between the circuit board, dash, and ignition switch is okay? NOTE: Before trying to perform the full field testing, I read that one common way to test modern alternators is to test for a magnetic field with a screwdriver once the switch is turned to the "on" position. However, I don't this will work on a Porsche -6 since it relies on the bulb to provide the resistance to "tickle" the alternator into charging. (Man I don't want to drop the engine for this....) - if light goes out on start, and you have battery volts at DF with ign ON not running, then "upstream" is all OK - the VR should be sending a signal to energize the field - ya gotta hope that field wire is attached correctly at the alternator i agree with your observation to Spoke about charging volts - "... minimum charging voltage is 13.8 volts dc across the battery terminals, or at the output of the alternator. A single lead-acid cell starts to charge at anything over 2.25 volts. Since a 12 volt battery has six cells, any 12 volt lead-acid battery needs at least 13.8 volts to start to charge. Testing battery and charging system - W8JI.com https://www.w8ji.com/battery_and_charging_system.htm - and if you turn on all the lights & loads it should kick up even higher, but will be regulated to 14.2-14.5 if your VR is good ... "To fully charge in reasonable times, alternator output must be 14.2 V to 14.5 V as measured right across the battery posts" (ibid) various sources will say "13.2-14.8" is the output range ( or more typically 13.8-14.2 means OK alternator) dunno about that magnet theory - (never heard that one before) where would you stick the screwdriver? - no way you can put it next to the alternator buried under the shroud - you might wanna test that idea on a different alternator on the bench engine drop - that's why our GT cars had a porthole in the back firewall - i have had alt out & back in thru that porthole several times over 25 yrs - it also makes timing & distributor & belt maintenance MUCH easier - i did enlarge my factory porthole a bit to make it easier the second time when the new IR Valeo 95-amp came with incorrect wiring diagram & I had exactly the problem you seem to be experiencing) (IMG:style_emoticons/default/rolleyes.gif) .... 2-days work cuz a vendor screwed up you might consider cutting one in - your car is enuf modified now that "originality" should not be a concern i think one of our vendors now sells a fiberglass cover for it, so you can use it for a pattern - (or i likely have an oem paper pattern stashed somewhere & could send it to you) (IMG:style_emoticons/default/stirthepot.gif) |
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