Why's my truck eating altinators

[Russ]

I'm on my 3rd rebuilt alt. in less than a year. At idle the gauge is on the left side of the needle swing(R in NORMAL) once I bring the revs above idle, up to about 1000 rpms it swings to the M -A. Is this normal or do I have something wrong. I've always thought it should always be on the + side of NORMAL even at idle.

 

[tjl]

Hey Russ, my needle always stays right in the middle at any rpm. The only time it moves around alot is when the glow plugs are on. I fryed a couple of alternators until I found a bad connection on the small wire on top of the alt. Check all your wires and connections. You can't just replace the plug either, you have to replace the entire harness from the ac compressor across to the solonoid on the fender.

 

[69oiler]

i fried my alt with a rubbed-thru wire coming out of the alt. look really close, i could hardly see the spot it rubbed thru. also, i'd use a multi-meter on the battery terminal to see if it's charging or not. 13-14 volts with the engine running.

 

[geonc]

Gary, check that small, single wire...it should have a plastic plug end.

Mine was showing erratic/low charging and when I wiggled that wire the guage would behave for a while......

Mine was destroyed......that seems to be a rather comfortable place to rest your arm when working on the eng

I ate one...auto zone replaced it under wtty....3 mos later another....so I went to a different town and got another
Fixed the wire and all is good!

There was enough slack so I just clipped off the bad end and replaced it with a spade connector used in residential A/C...designed for heavy loads and used double walled/adhesive lined heat shrink tubing to protect it.


just 1 place to check

 

[NJKen]

You need to get a real voltage reading before using a Ford "normal" guage to diagnose a problem. It is normal for the voltage to be a little lower at idle than an other time. As long as its staying above 13 you will never have a problem beause of that.
Good Luck
Ken

 

[Russ]

I check the volts and wires tomorrow when the sun come back up. It's dropping some volts because all of the the light dim.

 

[NJKen]

gloe plugs take a lot of power when they are on and that will agravate the problem.
Once you get some voltage readings you will have a better idea what is going on.
Ken

 

[Russ]

OK got some numbers
Before starting truck (cold) Batts read 12.28 volts
started with gp's on I get 11.4
after gp cycle. 13.9
turn on head lights volts drop to 12.9 and slowly falling
turn on blower+lights drop to 12.4 and slowly falling


Switch to high idle volts up to 14.2
turn on headlights drop to 14.1
lights + blower drop to 13.9


As long as I'm driving and above idle it's charging. but when ever I stop at a red light and have the blower and headlights on it starts to discharge


I checked the wires, no corrosion or chafed wires or lose connections. It jsut seams like at a lower rpm the alt just can't keep up with the blower motor and the lights. Should I worry about this or just drive it?

 

[sassyrel]

are you getting NEW, or REBUILT alts--and the reason i say it--is because some of the rebuilders aint the best--sounds like same problem i had, and when i checked it--the diode trio was out. i had a spare, and will finish the other when have time

 

[Russ]

Advance auto rebuilds. I have a local place that rebuilds them, I think that's where I'm headed next.

 

[JLDickmon]

OK got some numbers
Before starting truck (cold) Batts read 12.28 volts
started with gp's on I get 11.4
after gp cycle. 13.9
turn on head lights volts drop to 12.9 and slowly falling
turn on blower+lights drop to 12.4 and slowly falling


Switch to high idle volts up to 14.2
turn on headlights drop to 14.1
lights + blower drop to 13.9


As long as I'm driving and above idle it's charging. but when ever I stop at a red light and have the blower and headlights on it starts to discharge


I checked the wires, no corrosion or chafed wires or lose connections. It jsut seams like at a lower rpm the alt just can't keep up with the blower motor and the lights. Should I worry about this or just drive it?

no, replace the batteries
a fully charged battery at rest should be 12.66 volts

the other thing to do is check the voltage drop across a device, and do some simple math.. voltage drop + available voltage should equal source voltage

 

[82fordtruck]

Advance auto rebuilds. I have a local place that rebuilds them, I think that's where I'm headed next.

I think you found your problem. I think your solution will work fine.

 

[Russ]

Update. two new batts and the same ol' problem. I'm gonna get a local shop to rebuild my alt. Tired of the Mexicans crap.

 

[JLDickmon]

Update. two new batts and the same ol' problem. I'm gonna get a local shop to rebuild my alt. Tired of the Mexicans crap.

did you do your voltage drop tests yet?
and as far as changing out the alternator..
see if you can get a different (smaller) diameter pulley like out of a boneyard or something.. get that thing to spin a few more RPMs & see what happens

when I had bracket cars, we'd put a larger pulley on them to lower their output and reduce the drag they produce

 

[82fordtruck]

Update. two new batts and the same ol' problem. I'm gonna get a local shop to rebuild my alt. Tired of the Mexicans crap.

Your problem is likely a bad rectifier. The shop may just be able to sell you just the rectifier. There's a set of diodes in the back of the alternator that convert the alternating current to a DC signal. It essentially reverses the voltage when it would be negative voltage and uses a capacitor to smooth out the signal (think of the capacitor as a tank capable of holding electricity). If a diode is bad, you lose have the sine wave and have gaps between the waves. The capacitor smooths out the voltage some, but the resulting voltage is lower than what it would be if both parts of the wave were there. This problem is most noticeable at idle, when the waves are farthest apart.

Spinning the alternator faster will surely help, but it doesn't fix the problem.

Read here for more information:
http://en.wikipedia.org/wiki/Diode_bridge

Look specifically at the half wave rectified graph. THis is what you have now.