1991 Explorer XLT Voltage Ripple, Oscillation at speed or idle | Ford Explorer Forums - Serious Explorations

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1991 Explorer XLT Voltage Ripple, Oscillation at speed or idle

cbach1997

Member
Joined
October 25, 2008
Messages
26
Reaction score
3
City, State
Orange County, CA
Year, Model & Trim Level
'91 XLT
Hi everybody; thank you for taking time to read this.

My family is the original owner of said loved Explorer (1991 XLT, 4.0L RWD), 320,000 miles strong, but nobody can seem to pinpoint the cause of a very annoying oscillation. Very familiar behavior for old cars, I remember seeing old Accords and such with fluctuating headlights at stop lights. Everybody then seemed to think you'd need a new alternator, and that would solve it...

Well...Three alternators later (tried Autozone Chinese specials, am now back on a Motorcraft OE rebuilt), and there's no change. As I understand it, the voltage regulator is PART of the alternator assembly, so replace it, and you got a new regulator. I also know if I disconnect the alternator, the oscillation disappears... The oscillation does tie into engine speed.

It used to be something you'd only notice idling, but now sometimes it even goes bananas when driving down the road at speed.

Please help! Thank you so much in advance for your ideas. Below is a short clip of the behavior at highway speed.
https://www.dropbox.com/s/2osofblqzhn5d7n/91 Explorer voltage ripple.MOV?dl=0
 



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Mine did that when I had a bad alternator regulator. You are correct, the regulator is built into the alternator. Did you check all of the wires and connections from alternator to battery, grounds, starter, etc..?

If you have a volt meter, check the voltage coming from the alternator when the gauge is fluctuating. It might be a bad gauge.
 






The lights all flicker in unison with the gauge including headlights and dome lights so I think the gauge is telling the truth.
 






I had that happen, when the connection on the back of the alternator was getting loose.

Also, that wire, and the battery cables, may have corrosion inside, that can't be seen from the outside, and corrosion can cause enough resistance to give intermittent voltage flunctuations like you have there.
 






Our '92 does that once in a while.. It seems to do it when the battery is almost fully charged but right after starting. It's done it for years, even across different alternators and I have since changed the wire from the Alternator to the Battery and changed/added ground cables.

I'm also running a smaller pulley on the Alternator (IIRC, It's a 2" pulley while Stock is 2 5/8") which means the alternator can put out more amperage at idle... I had the issue before that change though but it seems to happen more often with the smaller pulley...

I'm not sure if that info helps, but I figured I'd throw it out there.

~Mark
 






Our '92 does that once in a while.. It seems to do it when the battery is almost fully charged but right after starting. It's done it for years, even across different alternators and I have since changed the wire from the Alternator to the Battery and changed/added ground cables.

I'm also running a smaller pulley on the Alternator (IIRC, It's a 2" pulley while Stock is 2 5/8") which means the alternator can put out more amperage at idle... I had the issue before that change though but it seems to happen more often with the smaller pulley...

I'm not sure if that info helps, but I figured I'd throw it out there.

~Mark
So I understand your post (thank you), the problem persisted after changing the alternator wiring? Did you completely replace that harness or only a portion? There are three leads on one large connector and a single lead on the back. My connection for that lead is worn and not terribly tight.
 






So I understand your post (thank you), the problem persisted after changing the alternator wiring? Did you completely replace that harness or only a portion? There are three leads on one large connector and a single lead on the back. My connection for that lead is worn and not terribly tight.

I changed the Ground wires and the Charge wire (alternator to Battery) and the one going from battery to solenoid and the one that goes from the solenoid to the starter I'm using 2 gauge thin strand stereo power/ground wires. I'm using Ground lugs from a household breaker box as my connections to the battery terminals.

Here's a photo from about 7 years ago... it was still after I did the changes to the wires and have since replaced the optima with another AGM battery that fits so I can use the stock battery hold down again.

4950524666_47205459ba_z.jpg
Optima Blue top in our '92 explorer by maniak_az, on Flickr

~Mark

edit: It's possible I used 4 AWG wire and not 2.. it's been many years since I did the change... I'd have to look at the wires to know for sure. I know it's definitely not bigger than 2.
 






Put your DMM (digital multimeter) on the battery terminals, then increase & decrease the engine RPM. The voltage shouldn't change much unless the battery itself is going away. Having used multiple alternators with the same result makes me suspicious of the battery. Did this start suddenly or get worse over time?
 






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