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Author Topic: 86 RC voltage fluctuation (FIXED!!!)  (Read 2013 times)

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Offline tungsoul

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86 RC voltage fluctuation (FIXED!!!)
« on: June 20, 2010, 09:28:35 AM »
I have an 86 RC 4x4. My problem is that when I turn on the headlights or use the power windows my voltage gauge jumps slightly to a lower voltage, below 12 volts. I had to put in a new key ignition a while back cause the old one locked up and broke which must have not quite been in the off position when that happened cause it caused my battery to die. After I put in the new ignition and put in a different battery out of my jeep it would work ok but everytime I would use something like the lights or windows the gauge would drop. I had the alternator bench tested and readings said it was bad. I replaced the alternator and the voltage regulator and added new grounds to whatever I could, ie block to frame, alternator to block, battery to rad support, battery to block. Its better but still only reads just 12volts and drops slightly when different items are used. I was told that if things were correct, my gauge should read over 12 volts, somewhere around 13.

Any and all help is always a welcome. You guys are the best around when it comes to the RC's
thanks again!!! ???
« Last Edit: June 26, 2010, 06:33:28 PM by s ǝoɾ »

Offline ToxicDoc

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Re: 86 RC voltage fluctuation
« Reply #1 on: June 20, 2010, 10:05:13 AM »
Voltage should not be less than 13.5 volts and up to 14.5 volts with the vehicle running.  Check the wiring.  The charge wire (larger wire) should be on tight.  Then check the field wires to the alternator.  One wire supplies system/battery voltage (switched), the other goes to the voltage regulator to be grounded by it as needed.
'85 W150 SB, 408 stroker, Magnum manifolds, Performer RPM, 670 Truck Avenger, HEI ignition, Auburn LSD 9.25 and '82 D44 (non-CAD) with 3.55/3.54,  NV4500/NP241

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Re: 86 RC voltage fluctuation
« Reply #2 on: June 20, 2010, 02:16:32 PM »
did you CLEAN the firewall were the VR bolts on / if it does not have a GOOD ground it,ll cause your problem / also pull apart the connectors at the back of the right valve cover and make sure they have a good connection
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Offline tungsoul

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Re: 86 RC voltage fluctuation
« Reply #3 on: June 20, 2010, 03:53:48 PM »
No I did not clean the firewall when I put on the new voltage regulator, I will do that next. I will also check the wire connections. Thanks again for all your help. will post findings.

Offline tungsoul

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Re: 86 RC voltage fluctuation
« Reply #4 on: June 21, 2010, 06:21:25 PM »
Ok still no luck. I checked all the connections and cleaned them. I cleaned the firewall and wire brushed the new paint off the voltage reg were the bolt holes are located. Replaced the wire connectors that attach to the alt with new ones. I checked the voltage at the battery with the vehicle running and I got 12.57 volts but still only read 12 volts on the gauge and when I turn on the lights it fluctuates. Whats next ? thanks again for all the help! :-\

Offline ToxicDoc

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Re: 86 RC voltage fluctuation
« Reply #5 on: June 21, 2010, 06:44:18 PM »
Check voltage at the alternator, both field terminals and the charge wire.  Report back and we will continue.
'85 W150 SB, 408 stroker, Magnum manifolds, Performer RPM, 670 Truck Avenger, HEI ignition, Auburn LSD 9.25 and '82 D44 (non-CAD) with 3.55/3.54,  NV4500/NP241

Offline s ǝoɾ

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Re: 86 RC voltage fluctuation
« Reply #6 on: June 21, 2010, 06:49:35 PM »
Load test the alternator....time for a new diode trio I surmise (much cheaper than a complete square back replacement alternator)
Avoid replacing any part that you have not proven to be faulty through extensive testing.

Offline ToxicDoc

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Re: 86 RC voltage fluctuation
« Reply #7 on: June 21, 2010, 06:55:57 PM »
Load test the alternator....time for a new diode trio I surmise (much cheaper than a complete square back replacement alternator)

Joe, this is the second alternator and no change in the situation, so I doubt it is a second one with an internal problem.  I'm still on the wire break somewhere theory.
'85 W150 SB, 408 stroker, Magnum manifolds, Performer RPM, 670 Truck Avenger, HEI ignition, Auburn LSD 9.25 and '82 D44 (non-CAD) with 3.55/3.54,  NV4500/NP241

Offline tungsoul

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Re: 86 RC voltage fluctuation
« Reply #8 on: June 21, 2010, 07:04:32 PM »
Yes this is the second alt. Not sure how to load test alt. Do you mean to turn on the lights or "put a load" on the system then check it with a digital multi meter. which probe to which wires?

Offline s ǝoɾ

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Re: 86 RC voltage fluctuation
« Reply #9 on: June 21, 2010, 07:38:32 PM »
Good point. Well there are some videos at the top of the page that will assist in cable testing.

Small green and blue wires, hint hint hint. Read more about them in the "confirmed fixes" thread.

If you are forced to buy another voltage regulator, buy "transpo C8313". May have to google that one unless you have an alternator specialty shop close by, because it is highly unlikely to be found at chain parts store.
Avoid replacing any part that you have not proven to be faulty through extensive testing.

Offline tungsoul

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Re: 86 RC voltage fluctuation
« Reply #10 on: June 22, 2010, 04:33:38 PM »
ok I will check what is said to do and post findings as soon as I can thanks again guys for all the help

Offline tungsoul

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Re: 86 RC voltage fluctuation
« Reply #11 on: June 23, 2010, 06:08:42 PM »
Ok I did a voltage drop test as suggested. Here are my findings

engine running battery voltage =  12.57volts
positive charging stud to positive post = 5.5volts  (I wasn't sure on which one the positive stud is, I thought it was the big black wire on the alternator) (not the ground wire)
green wire on alt to positive post =  10 volts
blue wire on alt to positive post = 9 volts

alternator case to negative post = .11 volts
voltage regulator mounting bolt to negative post = .10
 
I hope this sounds right not sure which wire, blue or green on the alt to check with positive post. I tried to find the info up top but was unable.

It looks like to me that the ground side is ok but the positive side is messed up. Should I run new wires from alt to reg. I think the service manual shows that there is a tie in to one of those wires or both inside the wire harness. thanks again for all the help

Offline s ǝoɾ

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Re: 86 RC voltage fluctuation
« Reply #12 on: June 23, 2010, 06:18:32 PM »
Ok I did a voltage drop test as suggested. Here are my findings

engine running battery voltage =  12.57volts
positive charging stud to positive post = 5.5volts  (I wasn't sure on which one the positive stud is, I thought it was the big black wire on the alternator) (not the ground wire)
green wire on alt to positive post =  10 volts
blue wire on alt to positive post = 9 volts

alternator case to negative post = .11 volts
voltage regulator mounting bolt to negative post = .10
 
I hope this sounds right not sure which wire, blue or green on the alt to check with positive post. I tried to find the info up top but was unable.

It looks like to me that the ground side is ok but the positive side is messed up. Should I run new wires from alt to reg. I think the service manual shows that there is a tie in to one of those wires or both inside the wire harness. thanks again for all the help

Problems.

Common sense will say if both leads are on a positive, how can you have a reading?

In a "perfect" world you would have a reading of 0. In real world a reading of 0 indicates other problems, but any reading over a few decimals such as .3 is also a problem.

I find it odd that you coincidentally have 2 different bad wires, but not surprising. OR there is a problem somewhere where they are spliced together?

I know everything meets at the battery post but do not know if they meet somewhere further down the line.
« Last Edit: June 23, 2010, 06:22:58 PM by s ǝoɾ »
Avoid replacing any part that you have not proven to be faulty through extensive testing.

Offline tungsoul

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Re: 86 RC voltage fluctuation
« Reply #13 on: June 23, 2010, 06:29:53 PM »
Common sense will say if both leads are on a positive, how can you have a reading?

Ok, I printed off what you wrote about checking the wires...... what I did was wrong?
can you please tell me which wire to check with the postive side battery post.
Is it the green one, the blue one or the big black one that is attached to a metal stud on the alt.
I apologize for my ignorance but I am learning was I go which is like gold to me. Thanks again for the help
 

Offline s ǝoɾ

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Re: 86 RC voltage fluctuation
« Reply #14 on: June 23, 2010, 06:55:15 PM »
You did things correctly as far as I know.

I was just trying to help you visualize what the test is accomplishing.

If you put both leads on the same battery post, what do you get? 0. So one would assume since the alt stud is also a positive, and so is the blue wire, you would also get 0.

I was simply explaining a reading like you have indicates the wire/connection in between your test points has a bad spot.
Avoid replacing any part that you have not proven to be faulty through extensive testing.

Offline tungsoul

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Re: 86 RC voltage fluctuation
« Reply #15 on: June 24, 2010, 04:46:01 PM »
I figured you were teaching me something, I do appreciate it Joe. Well I am going to try and carefully remove the wrapping that goes around the blue and green wires and see were the problem is and hopefully also replace those with new wires. At least if I still have the same problem I can rule those out. thanks again for all the help and I will post findings asap.

Offline s ǝoɾ

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Re: 86 RC voltage fluctuation
« Reply #16 on: June 24, 2010, 05:12:13 PM »
Your big alternator charge wire seems to also have a problem.

The problem may not be visible from the outside, can be completely internal. Or it can be something at the ends like a connection.

I will say it is hardest to measure the green wire, since it is very difficult to access both ends of it for testing, while remaining plugged in.
Avoid replacing any part that you have not proven to be faulty through extensive testing.

Offline tungsoul

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Re: 86 RC voltage fluctuation
« Reply #17 on: June 24, 2010, 07:03:32 PM »
Ok as of right now these are the things that I have done. I ran a jumper wire (good heavy wire) from the alternator to the voltage reg. First I ran the jumper wire from the blue wire on the alt to the vr. I kept the original wires hooked up but just spliced in carefully the jumper wire. I did this on both the blue and green wires, one at a time and so for no change in the voltage. My RC is running right now as I right this with still 12.25 volts measured at the battery post's. I also actually have the jumper hooked up to the blue wire to see if a little time with the motor running would show a difference in volt when I check the battery again.

 Not sure if this helps and or how long before I saw in a increase if any with the voltage.

Offline tungsoul

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Re: 86 RC voltage fluctuation
« Reply #18 on: June 24, 2010, 07:22:43 PM »
Well no luck with the jumper. Just went and checked the voltage at the battery and it read 12.21 so it actually dropped .03 volts in 15 minutes. Well I will check the big black wire tomorrow or this weekend and post my results asap. Thanks again for everyones help..

Offline tungsoul

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Re: 86 RC voltage fluctuation "SOLVED"!!!!!!!!!!!!!!!!!!!!
« Reply #19 on: June 25, 2010, 07:34:15 PM »
well I traced the wires from the alternator using my 86' RC service manual and found that the big black wire that attaches to the "post" on the alternator eventually ties into the red wire which goes to the starter relay which goes to the positive post on the battery. So I ran a jumper wire from the alternator strait over to the starter relay and hooked it up to the red wire and of course with the help of a barley pop (should've had one sooner) voltage jumped up immediatly the voltage went up to 13.75

 So now I am going to run a bigger wire from the alt and run it up to the fire wall and around and down to the starter relay. I just don't really want to dig into all of the sealed up wire looms and stuff to find the fault at this time.   Thanks again for everyones help. once again you guys come thru.
    Thanks Jamie

Offline ToxicDoc

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Re: 86 RC voltage fluctuation
« Reply #20 on: June 25, 2010, 08:58:18 PM »
Yup, you had a bad charge wire or connections.  Now you can enjoy a reliable charging system.  I'm using 6 ga. wire in anticipation of my upgraded alternator.
'85 W150 SB, 408 stroker, Magnum manifolds, Performer RPM, 670 Truck Avenger, HEI ignition, Auburn LSD 9.25 and '82 D44 (non-CAD) with 3.55/3.54,  NV4500/NP241

 

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