Elctrical Problem

When the 2003 Expedition idles the lights dim and brighten randomly. I checked the alternator. At idle it would charge at 14.2 and drop a little to maybe 13.9 and then pop back up to 14.2. It sometimes drops to 13.5 or 4ish and then pops back up. So I put a new alternator in..........same shit. I put in a spare battery....same problem. RPM's remain constant about 800rpm when the problem happens.

I replaced the belt. Old one had about 60k on it and still looked good. Tensioner looks like it is ok. No slipping/etc.

As far as I can tell, it only does this at idle. Lights don't dim while cruising.

Checked all the grounds fuses, electrical connections in the engine compart etc.

I have the wiring diagram...what is the best way to hunt down the problem? I almost feels like a large random draw...like the AC compressor cycling on/off....but the AC is not running.


:sos:

I forget what years, but Ford had a TSB about the charge wiring being undersized and cooking sometimes making for poor connections and vibration prone. They also used a double parallel fuse link setup at the solenoid on the core support.
Check those wires and links, clean the contacts and maybe some conductive grease will all help to cure it. A fast easy way to clean the wires ends is to dip them in a cup solution of baking soda.
Pretty sure the a/c will run even with the heat on in those cars and depending on the charge, but the charge should be a rather slow change downward as the battery gets charged, not jumpy.

010752 said:

I forget what years, but Ford had a TSB about the charge wiring being undersized and cooking sometimes making for poor connections and vibration prone. They also used a double parallel fuse link setup at the solenoid on the core support.
Check those wires and links, clean the contacts and maybe some conductive grease will all help to cure it. A fast easy way to clean the wires ends is to dip them in a cup solution of baking soda.
Pretty sure the a/c will run even with the heat on in those cars and depending on the charge, but the charge should be a rather slow change downward as the battery gets charged, not jumpy.

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Same thing happens with the AC on and cycling.

I searched for a TSB about the wire being undersized. Found quite a few others on the exped. electrical problems but couldn't find that one.

I did find quite a bit of info and complaints on one specific problem...windshield leakage letting water run down into the fuse box in the passenger kick panel corroding connections and causing all kinds of weird problems with the chassis electrical systems. Solution..remove the windshield/reseal and replace the fuse box.

I'll check and clean those wires...hopefully it is something that simple.

Thanks for the info.

My 2002 Vette does the same thing, but not only at idle. I can be driving down the road at night and the headlights will dim a little and then come right back. All in about 1 second. Art

I got embarassed by the silently slipping belt on the camper alternator...a CS144, but it has a V belt on it...NOW....at any rate, I"d turn on the power inverter, but when I'd hit the 110vac fridge, the inverter would beep and go with LO battery sometimes shut down....the freeking belt would allow slippage and system to go to battery power, since it's only a 24 seris battery NOW, the system would go wild....

tighten hell outta the belt and problem went away....

so take a wrench to the idler and instead of pulling it off like you change the belt...apply more tension....

it MAY be a sneaky silent slipper.....on a slithering serp belt.....

:bump::bump:

No luck so far.

I checked the charge connections and cleaned them up. The positive bat connection is a 3 wire set-up. One strait to the alt with a large fusible link. The second goes to the starter. The third looks like it goes into the electrical systems.

I ran it with the AC turned on and the compressor cycling. When it cycles "on", the engine speeds up a tad and the tensioner moves a bit. And the charge stays constant at about 14.1. It will drop to about 13.9 every so often but the lights don't dim.

With the AC off I ran the idle at 900/1000 rpm's( it idle's around 800). The charge rate remained constant at 14.2.

I wonder if the tensioner is causing the problem as per what Gene said?

Been going at this thing a little at a time. Now I am on to the interior. I got a feeling there might be an issue with the dash since so many others have had troubles with loose wires under there.

Thanks for the help guys!

Where are you measuring the charge, at the alternator positive post or the battery?

010752 said:

Where are you measuring the charge, at the alternator positive post or the battery?

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Measured at the Battery.

It really sounds like you're fine.
Alternators should max out around 14.7v depending on the regulator inside (lots available). If it stays at 14.7 at the battery, then you should have a weak battery.
You should only get that after a sitting a while and after running a bit it should drop to 14.2v or less but above 13.5v. Anything above a 14.2v-14.4v for extended periods is a "gassing charge" and will eventually fry your battery.

For fun you can put a "known bad battery" in and your charge at the alt should be around 14.7 and about 80% of the alt output.
I like to measure amps at the alternator for a quick test and if I get very high amps after a road test then the battery is usually bad.
For example 55 amps output initial on a rated 63amp GM SI alt, then down to 30 continuous vs 35 amps initial and down to 15 continuous with a new battery.

Probably cleaning your battery and charging connections caused your reading to stabilize a bit. I've had good luck using the copper antisieze on most connections.