erratic voltage issue
01-15-09, 08:57 PM
#1
erratic voltage issue
So here's the issue:
86 gxl w/ a sidemounted alternator
When I start her up she reads real low voltage, like 10, and remains that way until I get her up to 3500 or 4000. Usually anyway, today it stayed at ten until 15 minutes of driving, then up to 13 maybe. No real issues while driving, which I thought was strange considering 10 volts is nothing... so I switched out the alternator with a reman today on break and the same problem occurs! I'm thinking the issue is the sidemount slipping? But its on there nice and tight and up until today I had no problem reving up the volts at will after starting. So I'm stumped, I'm getting everything I nees to move the sidemount back to stock soon, but any ideas?
86 gxl w/ a sidemounted alternator
When I start her up she reads real low voltage, like 10, and remains that way until I get her up to 3500 or 4000. Usually anyway, today it stayed at ten until 15 minutes of driving, then up to 13 maybe. No real issues while driving, which I thought was strange considering 10 volts is nothing... so I switched out the alternator with a reman today on break and the same problem occurs! I'm thinking the issue is the sidemount slipping? But its on there nice and tight and up until today I had no problem reving up the volts at will after starting. So I'm stumped, I'm getting everything I nees to move the sidemount back to stock soon, but any ideas?
01-15-09, 10:12 PM
#4
HAILERS
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The alternator needs excitation voltage to get started. ON a series four or five it's the L wire. It's white/black on a series four.
An alternator can get excitation (for the field voltage) from the residual magnatism in the rotor if the engine is rev'd high. After that the excitation will come from the diode trio.
IF the warning lights on your series four do not all come on when the key is put to ON, engine OFF, then most likely the excitation voltage on the white/black wire isn't there, and that is your problem. Or the wire is off the alternator.
I can duplicate your problem on any series four alternator and most series five imho.
With the key ON, engine OFF, and if you backprobe the white/black wire at the alternator, you should see 1-3vdc (its in the FSM). That is the excitation voltage. If you pull that plug off and measure the voltage on the white/black, you should see basically batt voltage like 12vdc. That is voltage being read thru the coil of the Alt relay in the CPU. It drops to 1-3vdc when the plug is connected up to the alternator. Series four.
An alternator can get excitation (for the field voltage) from the residual magnatism in the rotor if the engine is rev'd high. After that the excitation will come from the diode trio.
IF the warning lights on your series four do not all come on when the key is put to ON, engine OFF, then most likely the excitation voltage on the white/black wire isn't there, and that is your problem. Or the wire is off the alternator.
I can duplicate your problem on any series four alternator and most series five imho.
With the key ON, engine OFF, and if you backprobe the white/black wire at the alternator, you should see 1-3vdc (its in the FSM). That is the excitation voltage. If you pull that plug off and measure the voltage on the white/black, you should see basically batt voltage like 12vdc. That is voltage being read thru the coil of the Alt relay in the CPU. It drops to 1-3vdc when the plug is connected up to the alternator. Series four.
01-15-09, 10:48 PM
#5
Ok hailers, bear with me; I'm not very electrical savvy but you've made it pretty clear that I need to check the exciter wire. Aka the L wire. My lights do not all lgiht up with ignition on, so that's pretty clear that that is the problem. Now it is connected to the alternator however, so then either the warning lights are out or the wire is shorting somewhere then and I need to repair the harness?
01-16-09, 09:48 AM
#7
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No. The L wire comes from a relay in the CPU on a series four car.
You need to turn the key to ON and see if there is any voltage on the white/black wire or not. It's hard to believe that wire would be open, but might be.
Series Five L wires do not use the relay in the CPU. The wire goes to the warning light assy.
The series four L wire goes to the relay in the CPU. It puts a ground on that relay which in turn then pulls in and sends a ground to the warning light assy.
The lights in the warning light assy might not be coming *all on* with the key to ON, because of bad solder joints in the warniing light assy.
On a series four, you should be able to put the key to ON, engine OFF, and apply a ground to the white/black wire. That should cause all the warning lights to come on. You should be able to hear the relay in the CPU click when the ground is put on the white/black wire. If the relay clicks, but all the warning lights don't come on, then you have bad solder joints in the warning light assy.
The lights themselves don't excite the alternator. It's the elect feed from the CPU alt relay coil that excites the field in the alternator. That's why I suggest pulling the plug off the alt and seeing if there is approx 12 vdc on that white/black wire. IF there is, then I'm wrong about why you have to rev the engine to get the alternator to get put out.
Don't run a new wire to anywhere. If you put a ground on the wrong wire in the plug...the Black/White wire, then you'll blow a fuse.
You need to turn the key to ON and see if there is any voltage on the white/black wire or not. It's hard to believe that wire would be open, but might be.
Series Five L wires do not use the relay in the CPU. The wire goes to the warning light assy.
The series four L wire goes to the relay in the CPU. It puts a ground on that relay which in turn then pulls in and sends a ground to the warning light assy.
The lights in the warning light assy might not be coming *all on* with the key to ON, because of bad solder joints in the warniing light assy.
On a series four, you should be able to put the key to ON, engine OFF, and apply a ground to the white/black wire. That should cause all the warning lights to come on. You should be able to hear the relay in the CPU click when the ground is put on the white/black wire. If the relay clicks, but all the warning lights don't come on, then you have bad solder joints in the warning light assy.
The lights themselves don't excite the alternator. It's the elect feed from the CPU alt relay coil that excites the field in the alternator. That's why I suggest pulling the plug off the alt and seeing if there is approx 12 vdc on that white/black wire. IF there is, then I'm wrong about why you have to rev the engine to get the alternator to get put out.
Don't run a new wire to anywhere. If you put a ground on the wrong wire in the plug...the Black/White wire, then you'll blow a fuse.
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01-16-09, 02:58 PM
#11
Ok, here are the results:
W ignition off, white/black wire reads 8 volts
W ignition on, same thing. 8 volts
When unplugged the connector side reads 0 and the alternator side reads 8 volts still
Battery reads 11.8 volts
I need to find some wire to ground the l wire....
W ignition off, white/black wire reads 8 volts
W ignition on, same thing. 8 volts
When unplugged the connector side reads 0 and the alternator side reads 8 volts still
Battery reads 11.8 volts
I need to find some wire to ground the l wire....
01-16-09, 03:18 PM
#13
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With the key OFF, the white/black wire shouldn't read anything.
Put the key ON, and it should read about batt voltage.
IF it reads approx batt voltage with the key ON, then that should have been enough to excite the field in the Alternator.
The Black/White should read zero with the key off and batt voltage with the key to ON or better.
So the alternator should be working. Next time start and idle the engine, the put your meter on the B terminal of the battery and see how much it read. Don't do any trick high reving, just start the engine and measure the voltage on the large output terminal on the alternator *B* terminal.
Put the key ON, and it should read about batt voltage.
IF it reads approx batt voltage with the key ON, then that should have been enough to excite the field in the Alternator.
The Black/White should read zero with the key off and batt voltage with the key to ON or better.
So the alternator should be working. Next time start and idle the engine, the put your meter on the B terminal of the battery and see how much it read. Don't do any trick high reving, just start the engine and measure the voltage on the large output terminal on the alternator *B* terminal.
01-16-09, 04:10 PM
#16
sorry to post so much, but if i bypass the relay it would excite the alternator yes? since the alt is side mounted i could tie into the extension on there and not have to worry about grounding out the black/white wire. is this feasible? im stuck on this side of town and just need to get home where i can really work on the girl.
01-16-09, 05:37 PM
#17
greeeat success!
Well I got it home! Jumpered the L terminal to the + post on the battery to get the alternator excited and voila! Just like the article said. Thanks for the help again hailers! Ill pop out the warning lights and repair the cold solders tomorrow morning to fix it for sure. The offer is still up for that beer by the way, just come by the covey and get yourself a cold one on me!
01-16-09, 06:02 PM
#18
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What you have on the white/black is good enough for the thing to work. The relay actually does not have to pull in. All that is needed is for the voltage to pass thru the coil on the relay to the alternator field. You seem to have that. The alternator should have started working right upon start up.
The relay does have to pull in for the Warning lights to come on. In particular the Charge light in the warning light cluster. Series four cars are notorious for that warning light assy to fail due to bad solder connections where the elect plug attaches.
I'd connect a meter to the large output terminal and see what the thing is putting out at idle and say ...2500rpm or so. Should be 14vdc to 14.7vdc . If you read the voltage at the battery, bad cables and ??? can make it read somewhat lower, like 13.5-14vdc.
Again, it takes but a small amount of voltage/current to make the field of the alt excite. Don't run a new wire from some other source. Use the original wiring.
With the key to ON, you should be able to find a short piece of wire bare at each end, and put one end on a known gnd (like the alternators body) and the other end into the connector where the white/black wire is. You should be able to hear a click from the relay in the CPU and the warning lights should come on. The plug should be OFF the alternator when you do that. Engine off, key ON. IF you hear the relay pull in, but the warning lights not come on, then you have a slight problem with the solder joints on the Warning Light assy.
You have a two *problems*. One is the warning lights not coming on when the key is to ON, and the other problem in the alternator not charging right away when at idle (you say you have to rev the engine before it puts out). Well with the voltage you have on that white/black wire, that should have done the job. So I don't understand why the thing is acting up.
Do you have a smaller than stock main pulley on the e-shaft? That might be a slight problem at low engine speeds.
IF the belt was loose it seems you'd notice that or hear it slipping.
The relay does have to pull in for the Warning lights to come on. In particular the Charge light in the warning light cluster. Series four cars are notorious for that warning light assy to fail due to bad solder connections where the elect plug attaches.
I'd connect a meter to the large output terminal and see what the thing is putting out at idle and say ...2500rpm or so. Should be 14vdc to 14.7vdc . If you read the voltage at the battery, bad cables and ??? can make it read somewhat lower, like 13.5-14vdc.
Again, it takes but a small amount of voltage/current to make the field of the alt excite. Don't run a new wire from some other source. Use the original wiring.
With the key to ON, you should be able to find a short piece of wire bare at each end, and put one end on a known gnd (like the alternators body) and the other end into the connector where the white/black wire is. You should be able to hear a click from the relay in the CPU and the warning lights should come on. The plug should be OFF the alternator when you do that. Engine off, key ON. IF you hear the relay pull in, but the warning lights not come on, then you have a slight problem with the solder joints on the Warning Light assy.
You have a two *problems*. One is the warning lights not coming on when the key is to ON, and the other problem in the alternator not charging right away when at idle (you say you have to rev the engine before it puts out). Well with the voltage you have on that white/black wire, that should have done the job. So I don't understand why the thing is acting up.
Do you have a smaller than stock main pulley on the e-shaft? That might be a slight problem at low engine speeds.
IF the belt was loose it seems you'd notice that or hear it slipping.
01-16-09, 06:53 PM
#19
Right, i grounded the white/black wire to the alt body with plug offand read zero volts, like i said above. the alternator is not self exciting anymore, even after ten to fifteen minutes of varying rpms. i sat and watched the voltage drop from the b terminal stay at a constant 8 volts before jumping a wire from the white/black wire to the posotive battery terminal. just long enough to excite the alternator. the voltage raised to around 12.9 to 13.1 voltage and stays consant.
i didnt hear the relay click when the white/black wire was grounded. the belts not loose, and stock pulley. everything is hooked up right.
sorry for the bad typing, im doing this from my phone.
i didnt hear the relay click when the white/black wire was grounded. the belts not loose, and stock pulley. everything is hooked up right.
sorry for the bad typing, im doing this from my phone.
Last edited by texFCturboII; 01-16-09 at 07:03 PM. Reason: clarification
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