1986 4.9 w/G2 alternator OVERCHARGING

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1986 4.9 w/G2 alternator OVERCHARGING

FunWithPaul
Hi guys,
I have an 1986 F150 with the 4.9 straight six and a 2G alternator. The wiring seems to have been "adapted", because it doesn't match any of the diagrams that I have found.

Last time I used it, the alternator belt started squealing and the amp meter went to 3/4. The voltage went to 16.8!

I unplugged the onboard regulator, and got home before the battery died...

I have tried EVERYTHING (I think) since then, trying to diagnose the problem.

Part of my diagnosing issue though, is that the wiring doesn't match any of the published diagrams...

I have this:



Here are some pics for proof:








It puts out 16.8v anytime the yellow wire is connected to the regulator.
The green wire is battery voltage (slightly less, maybe .5v) when the ignition is on.
The wires all check for continuity.

I have removed and installed this alternator about 6 times today...
I have removed the regulator, swapped the brushes (one is a little worn) cleaned all of the contacts and even put in a ground wire (in case a bad ground was the issue)

I even rewired it to 2G specs (using jumpers) connecting the S to the S, and I to ignition power, and that didn't change anything.

Still 16.8v,  anytime the A terminal is connected to 12v.


Any suggestions??

Thanks,
Paul

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Re: 1986 4.9 w/G2 alternator OVERCHARGING

ArdWrknTrk
Administrator
This post was updated on .
Other than upgrading to a 3G?  

Regulators DO go bad, and are available almost anywhere for ~$10.

I would have said it was the yellow 'sense' wire, but you say it checks out..

I might try jumpering from the output splice (where the two bk/or wires splice to the fusible link) over to the yellow.
That would definitely narrow it down to the regulator itself.
 Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.
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Re: 1986 4.9 w/G2 alternator OVERCHARGING

ArdWrknTrk
Administrator
Does the voltage go *up if you "ground here to test" and set it full field?
 Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.
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Re: 1986 4.9 w/G2 alternator OVERCHARGING

FunWithPaul
Thanks for the replies.

I did order a regulator "just in case"...
It came in last night.

I decided to install it and rewire the connections so the "I pin" gets ignition, instead of the "S pin" (the way it WAS wired)

I couldn't swap sockets in the plug, so I cut it off and put on small female spade terminals insulated with heat shrink (I have a new plug on the way...)

I double checked all of the voltages (Bat voltage at the yellow wire and ignition power at the green wire),
put the alternator back in, started it up and got 14.4 volts!

I guess it WAS the regulator (but why it worked with the ignition power connected to the S pin stumps me)

Thanks!
Paul

 
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Re: 1986 4.9 w/G2 alternator OVERCHARGING

FunWithPaul
In reply to this post by ArdWrknTrk
To answer your second question (does the voltage go up if the F screw is shorted):
No. It was already at 16.8 to 17v
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Re: 1986 4.9 w/G2 alternator OVERCHARGING

85lebaront2
Administrator
In reply to this post by FunWithPaul
The designations on the regulator plug are A - Alternator, that is the actual voltage sense wire, S - Stator which was used on some applications, I - Indicator (idiot light) this "tickles" the alternator to start it charging. I would suspect when you made the temporary repair you started it seeing the correct charging voltage.

The big fault with the 2G is it's output plug developing high resistance due to age, corrosion and even vibration, this starts a vicious cycle where the alternator is working harder to reach it's design output. On the pre 1987 trucks with the 2G, the genius who designed the wiring should have been shot. The alternator voltage sense point is at the junction of Fuse Link J and the BK/O shunt for the ammeter, which in theory is battery voltage, but for some reason results in the alternator seeing lower that actual voltage. The later systems with the 3G are much better, but the ammeter shunt does limit the total usable output.
Bill AKA "LOBO" Profile

"Getting old is inevitable, growing up is optional" Darth Vader 1986 F350 460 converted to MAF/SEFI, E4OD 12X3 1/2 rear brakes, traction loc 3:55 gear, 160 amp 3G alternator Wife's 2011 Flex Limited Daily Driver 2009 Flex Limited with factory tow package Project car 1986 Chrysler LeBaron convertible 2.2L Turbo II, modified A413

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Re: 1986 4.9 w/G2 alternator OVERCHARGING

ArdWrknTrk
Administrator
In reply to this post by FunWithPaul
If you're going to continue with the 2G I would HIGHLY recommend changing the charge plug as outlined in the TSB shown under the 3G upgrade page. Resources--> electrical --> 3G alternator.

I finally got sick of dead batteries and charging issues.
I wish I had done the swap in '92 instead of '07
 Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.