'04 Exp--3 stalls while driving, now "Check Charging System"

[usn.mustanger]

So my 2004 XLT Explorer just recently started misbehaving.
3 times in the last week, the engine simply quite while driving at low speed (25-30mph), but never at higher speeds. Engine would restart immediately, no problem. No other issues or symptoms were observed...until yesterday.

Now, while it hasn't stalled in a few days, I'm getting the dreaded "Check charging system" error message. At first, it would go away when I accelerated, and didn't come on at all on the freeway, but now it's nearly always on, cycling on and off rapidly (I guess as alternator voltage seems to be hovering around the alarm threshold), until it locks in at speed.

I hooked up a cheap OBD II reader yesterday, and with the engine running at idle, DC voltage was reading 11.9V +/- .1V. Revving the engine in neutral never got me above 12.1V tops. With the ignition switch off, I get a solid 12.2-12.5V, so I'm pretty sure the battery is good (and it was just replaced several months ago).

The V meter in the instrument cluster is a tad lower than normal, just below the mid-mark.

There is no noise coming from the belt, idler pulley or tensioner.

So the initial stalls originally led me to think the ignition switch was bad, but now the voltage issues lead me to believe that the alternator is going bad. Surely these two problems are related, but I have a hard time believing that both the ignition switch AND the alternator are going bad *at the same time*.

1) Can the stalls be caused by an alternator starting to go south? Or...
2) Can the "Check charging system" issues be caused by a faulty ignition switch? Or...
3) Is it something else altogether?

Thanks in advance for any help!

 

[decipha]

from what your describing it sounds like a bad alternator

 

[usn.mustanger]

SOLVED: It was the alternator. She gave up the ghost today. Happened pretty quickly too. I barely made it to work. Instrument cluster, radio, etc. all died, but the engine kept going right until I got to the parking lot. Phew! Was able to score a new one pretty quickly and swap it out right there in the parking lot at work.

One question remains--the initial stalls...could these have been caused by the alternator? These happened before any bad alternator symptoms displayed (low voltage, "check charging system" warning), and I didn't think on-road stalls, in the absence of any other problems, were caused by a bad alternator in the early stages of failure. Hrm...

 

[Joe in NY]

If the voltage is too low you wont get good spark, injector cycles, and the PCM will be struggling. Computers do all sorts of funky stuff at low voltage. Fail-safe is to just shutdown.

 

[usn.mustanger]

If the voltage is too low you wont get good spark, injector cycles, and the PCM will be struggling. Computers do all sorts of funky stuff at low voltage. Fail-safe is to just shutdown.

But that's just it--the voltage wasn't really that low (~12.9V) when the stalls happened. And then when voltage was really low (as in everything except the engine itself was shutting down), the engine still ran just fine, no stalls. (At least until I parked, it, and the car said "no more!") My concern is that there might still be a separate issue (like a sporadically bad ignition switch) in there.

Guess the only way I'll know is to keep driving and wait and see...

 

[Tonybanksfan]

But that's just it--the voltage wasn't really that low (~12.9V) when the stalls happened. And then when voltage was really low (as in everything except the engine itself was shutting down), the engine still ran just fine, no stalls. (At least until I parked, it, and the car said "no more!") My concern is that there might still be a separate issue (like a sporadically bad ignition switch) in there.

Guess the only way I'll know is to keep driving and wait and see...

What happened was one of the brushs in your alternator wore out but not the other. You need both brushs making firm contact to create full voltage. When the one brush was deteriorating but not quite worn out, you get varying voltages at different rpm's. Higher rpm's were just enough to keep your voltage up. Lower speeds were causing your voltage to randomly dip below 12.2 volts or so, causing the stalls. The alternator died a slow death due to the the time it took to wear down the one bad brush until finally there was not enough material left to make proper contact. If you disassemble the voltage Regulator brush assembly on your alternator I guarantee you will find one good brush and one worn beyond limits or even broken and crumpled. Your problems are over. Next time check your brushs and buy the assembly instead of the whole alternator to save some dollars. Course there's nothing wrong with a whole new alternator unit for years of worry free operation.

 

[imp]

What happened was one of the brushs in your alternator wore out but not the other. You need both brushs making firm contact to create full voltage. When the one brush was deteriorating but not quite worn out, you get varying voltages at different rpm's. Higher rpm's were just enough to keep your voltage up. Lower speeds were causing your voltage to randomly dip below 12.2 volts or so, causing the stalls. The alternator died a slow death due to the the time it took to wear down the one bad brush until finally there was not enough material left to make proper contact. If you disassemble the voltage Regulator brush assembly on your alternator I guarantee you will find one good brush and one worn beyond limits or even broken and crumpled. Your problems are over. Next time check your brushs and buy the assembly instead of the whole alternator to save some dollars. Course there's nothing wrong with a whole new alternator unit for years of worry free operation.

@Tonybanksfan
Most interesting theorizing! But before making personal guarantees, I see possible flack coming back at you. Why should one brush wear beyond that of the other? How often does that happen? (Every single brush-holder I have examined over the past 50+ years of alternator usage has had equal brush wear).

However, I will concede that one brush might crumble, or crack, but the effect would be well-beyond the result described.

Or, your experience related to alternators greatly exceeds my own, which is entirely possible, as my work involved deep involvement in all aspects of automotive failure analysis, not focused on any one particular trouble-spot. imp

 

[Tonybanksfan]

Only a post mortem of his unit will verify my theory. Yes the vast majority of alternator brush wear is equal, but I have seen this problem multiple times over the last 40 years of repairs. Sometimes unequal wear is caused by manufacturer or material defects, and sometimes it's caused by dirt or some other foreign particle getting lodged in or behind the brush housing. Sometimes the brush spring tension can be affected by contaminants which can create uneven pressure resulting in different brush wear rates.
Regardless, I guess I should never be ****y enough to make guarantees without having my hands on it.

 

[usn.mustanger]

Quick update...since installing the new alternator, while Voltage is a solid 14+ volts, I have had one on-road low-speed (~20mph) engine stall. Might need a new ignition switch after all...

 

[Joe in NY]

What happened was one of the brushs in your alternator wore out but not the other. You need both brushs making firm contact to create full voltage. When the one brush was deteriorating but not quite worn out, you get varying voltages at different rpm's. Higher rpm's were just enough to keep your voltage up. Lower speeds were causing your voltage to randomly dip below 12.2 volts or so, causing the stalls. The alternator died a slow death due to the the time it took to wear down the one bad brush until finally there was not enough material left to make proper contact. If you disassemble the voltage Regulator brush assembly on your alternator I guarantee you will find one good brush and one worn beyond limits or even broken and crumpled. Your problems are over. Next time check your brushs and buy the assembly instead of the whole alternator to save some dollars. Course there's nothing wrong with a whole new alternator unit for years of worry free operation.

Just a little FYI:
Old style generators rely on brushes for full current.

Alternators are 3 phase AC generators that rectify and regulate to 14V DC. They DO have brushes but only to setup the magnetic field when you first start the car. Once the field is generated the brushes do nothing.