What causing voltage to dip?
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Mountain Pass
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What causing voltage to dip?
I have a 1986 bullnose with 302 engine. For some reason the voltage is dipping causing the headlights to temporarily dim, or the heater to temporarily blow less. And if voltage tips the needle on the gauge dips also. I have replaced alternator and regulator with no luck. What else could cause this and what other tests can I do to narrow down this problem? video below:
FTE Legend
Joined: Nov 2015
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From: Angier, NC
Is this at idle or at 2000 RPM?
I would start by replacing all the battery cables unless you just did them a year ago.
And no you can not look at the cables to tell if they are good just replace them.
When replacing them clean all the grounds really good.
Battery to motor, motor to frame and motor to cab / body.
Also check to make sure the ground from the regulator to ALT is good.
Dave ----
I would start by replacing all the battery cables unless you just did them a year ago.
And no you can not look at the cables to tell if they are good just replace them.
When replacing them clean all the grounds really good.
Battery to motor, motor to frame and motor to cab / body.
Also check to make sure the ground from the regulator to ALT is good.
Dave ----
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From: Virginia
Does your truck have the famous 2G alternator where all it has on it is two plugs for the electrical? If so, did you inspect the plug with the two large wires carefully? They like to burn up. If you do have a 2G, then there would have been a warning in the paperwork that they would not warranty the alternator if you did not replace that plug.
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Mountain Pass
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I have done the 3G upgrade and I am no longer using that plug with the two black and orange wires in it. I have not replaced all the other cables yet. And this happens at idle. Thank you for helping me
Post Fiend
Joined: Apr 2002
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From: Waterloo, Iowa
That is by definition a classic voltage regulation problem. Voltage is sagging or surging, fluctuating. The question of course is "why", what is causing that. Loose, missing, or corroded ground straps are a good way to do that. Want to find the cause and fix it, because stuff can get roasted, or that may be why the regulator is lunched in the first place.
It is very important that everything is at the same ground potential as the battery ground terminal. This means the frame, engine block, alternator, and firewall are all tied together. Years ago the charging system voltage regulator was a separate unit, mounted on a fender or firewall. If it had a poor or lifted ground plane connection it would get "confused". Same thing applies today. The alternator itself needs a clean tight connection to the block itself. Restored cars and trucks with fresh paint on everything and then assembled can cause trouble, but it's usually usually corrosion or rust is the problem. Check the alternator for AC ripple or failed diodes too.
It is very important that everything is at the same ground potential as the battery ground terminal. This means the frame, engine block, alternator, and firewall are all tied together. Years ago the charging system voltage regulator was a separate unit, mounted on a fender or firewall. If it had a poor or lifted ground plane connection it would get "confused". Same thing applies today. The alternator itself needs a clean tight connection to the block itself. Restored cars and trucks with fresh paint on everything and then assembled can cause trouble, but it's usually usually corrosion or rust is the problem. Check the alternator for AC ripple or failed diodes too.
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Mountain Pass
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Thank you so much. I noticed when I remove the old alternator it did not have a ground strap on it, I asked around and people said I didn’t need to add a ground strap to the new one. Now I’m beginning to wonder. Should I ground it? I am thinking based on your answer I should.
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From: Virginia
I have only had to add a ground to the alternator on very rusty trucks. Do you have any large loads on the the electrical system when the rpm dips? If you have a large load on it, and the rpm dips for some other reason, the voltage will naturally dip also. Sort of a chicken or the egg thing. You will have to figure out if the voltage dip is causing the rpm problem, or the rpm problem is causing the voltage dip.
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Post Fiend
Joined: Apr 2002
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From: Waterloo, Iowa
Thank you so much. I noticed when I remove the old alternator it did not have a ground strap on it, I asked around and people said I didn’t need to add a ground strap to the new one. Now I’m beginning to wonder. Should I ground it? I am thinking based on your answer I should.
For testing an alternator it is always done while it's under load. Turn the headlights on HI beam, crank up the heater blower or AC if you have it. Then raise the engine RPM to about 2000 or so while in neutral and hold it there. Measure the battery voltage directly at the battery posts. It will sag some but it shouldn't be a whole lot. You might actually be running way too high of a voltage, and what you think is the "sag" is when it drops back to normal.
At a normal idle RPM with no accessories running typically will see 13.8 to 14.3 volts something like that, in moderate weather temperatures.
FTE Legend
Joined: Nov 2015
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From: Angier, NC
I don't get the "I have replaced alternator and regulator with no luck." and then you post later you did a 3G ALT upgrade?
IIRC the 3G ALT has a built in regulator so what gives?
Also you say the AMP gauge is moving, I don't know of anyone that has seen it move but you also have a 3G ALT upgrade.
I thought you bypassed the AMP gauge with the 3G or you could have melted wires / fire, passing all the power thru the shunt & gauge?
How was the 3G wired into the truck and why was it done? Was it to ditch the 2G fire starter ALT?
Dave ----
IIRC the 3G ALT has a built in regulator so what gives?
Also you say the AMP gauge is moving, I don't know of anyone that has seen it move but you also have a 3G ALT upgrade.
I thought you bypassed the AMP gauge with the 3G or you could have melted wires / fire, passing all the power thru the shunt & gauge?
How was the 3G wired into the truck and why was it done? Was it to ditch the 2G fire starter ALT?
Dave ----
Thread Starter
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Mountain Pass
Joined: Jul 2020
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Also you say the AMP gauge is moving, I don't know of anyone that has seen it move but you also have a 3G ALT upgrade.
I thought you bypassed the AMP gauge with the 3G or you could have melted wires / fire, passing all the power thru the shunt & gauge?
How was the 3G wired into the truck and why was it done? Was it to ditch the 2G fire starter ALT?
I thought you bypassed the AMP gauge with the 3G or you could have melted wires / fire, passing all the power thru the shunt & gauge?
How was the 3G wired into the truck and why was it done? Was it to ditch the 2G fire starter ALT?
- but please correct me if I’m wrong.
I reused the existing plug 2. Plug 1 I removed and only used the existing white wire from it. It was my understanding that plug one is the one that creates meltdowns and fires and so forth? .
FTE Legend
Joined: Nov 2015
Posts: 30,876
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From: Angier, NC
I have not done this swap but have seen post that a shunt needs to be bypassed.
I will see what I can come out with but I am sure someone will be by that has done this or knows for sure what to do.
Try this link, I did not go through it but was up top in the "How To" area.
https://www.ford-trucks.com/forums/1...tallation.html
Can try this link as it also has some other information that may be of help from another 80-86 Ford truck site.
I would look at this one first and the tabs on wiring & AMP / Volt gauge.
Resources - Electrical
Dave ----
I will see what I can come out with but I am sure someone will be by that has done this or knows for sure what to do.
Try this link, I did not go through it but was up top in the "How To" area.
https://www.ford-trucks.com/forums/1...tallation.html
Can try this link as it also has some other information that may be of help from another 80-86 Ford truck site.
I would look at this one first and the tabs on wiring & AMP / Volt gauge.
Resources - Electrical
Dave ----
Cargo Master
Joined: Mar 2008
Posts: 2,563
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From: Washington
Reference post 12 photo, "Plug 2"
I did a 2G to 3G swap on my 1986. I also tried to reuse the Voltage Regulator (VR) plug, it didn't work, the Alt would not charge.
I really wasn't surprised it didn't work, I kind of expected it to not work based on what I had read. On 1986 2G factory installed ALT, the VR plug only has 2 of the 3 wires, which I guess must have worked fine for VR's made back in the late 1980's. But it seems that current VR need all 3 inputs to work. This also goes for a new replacement 2G ALT install, you are going to need a new plug with 3 wires on the VR to get it to work. And on a side note, when you take the ALT back to the store because it doesn't charge due to the 2 wire plug, they will test it out, using a 3 wire plug on the VR, meaning it works fine on the bench.
Look at this link...
https://www.ford-trucks.com/forums/1...l#post14726314
Power going to your fuse box will cause the amp meter to read discharge.
Jim
I did a 2G to 3G swap on my 1986. I also tried to reuse the Voltage Regulator (VR) plug, it didn't work, the Alt would not charge.
I really wasn't surprised it didn't work, I kind of expected it to not work based on what I had read. On 1986 2G factory installed ALT, the VR plug only has 2 of the 3 wires, which I guess must have worked fine for VR's made back in the late 1980's. But it seems that current VR need all 3 inputs to work. This also goes for a new replacement 2G ALT install, you are going to need a new plug with 3 wires on the VR to get it to work. And on a side note, when you take the ALT back to the store because it doesn't charge due to the 2 wire plug, they will test it out, using a 3 wire plug on the VR, meaning it works fine on the bench.
Look at this link...
https://www.ford-trucks.com/forums/1...l#post14726314
Power going to your fuse box will cause the amp meter to read discharge.
Jim