Effects of Failing Alternator

[gw33gp]

Yesterday, my alternator totally failed on me. My first indication of a problem was the check 'engine light' came on but that could have been an EGR code that has been popping up on me. The next thing I noticed was the tach started acting erratically and eventually went to zero with the engine running. Then the speedometer read 10 mph while stopped at a stop light. I think the ABS light was the last warning lights to come on. Just a few block before my destination the engine began losing power but was able to get me there. When I parked it would idle but very rough. I shut it down and tried to restart but just got clicking.

I have one of those small Lithium ion jumper batteries and tried that. It started right up and ran fine. I had about 11 miles to get home so I took off work before dark to see if that Lithium battery would have enough power to get me home. It did but the last 1/2 mile was marginal. I should have disconnected the dead battery because I realized later that the jumper battery was running the engine and recharging the dead battery. I pulled the alternator and took it to be checked and it was not putting out anything. I ordered a new one and it will be installed tonight.

I have been getting an DTC code lately indicating 'insufficient flow' on the EGR system and thought I had narrowed it down to the DPFE sensor. After all the strange electronic problems that popped up as the alternator failed, I was wondering if the failing alternator may have contributed to the EGR code. I guess I will find out after I install the new alternator and see if the code comes back.

 

[85_Ranger4x4]

They do goofy things.

When the one died in dad's '05 F-150 the automatic 4wd hubs started buzzing because there wasn't enough power to hold them fully in the disengaged position.

 

[Mark_88]

Yes, the alternator going out can take a few things along with it...or seemingly do so. I've had all the symptoms you described caused by a wonky alternator too...they started about a day before I realized what was happening and was baffled.

After the new alternator is installed you will have reset the computer (if not do so) to see if the EGR codes pop up or disappear that that will determine if they were related or not.

I've seen this hundreds of times though...two or more unrelated issues pop up at or around the same time and frustrate the carp out of everyone involved.

 

[RonD]

2002 has a "Battery Light"(charge indicator)

And that didn't come on?

Battery light circuit is pretty simple, a 12volt light bulb will light up if one leg has 12volts and the other leg is grounded(or lower than 12volts)
If both legs have 12volts then no power passes thru the bulb and it is OFF

When you turn on the key one leg gets 12volts, the other leg is connected to alternator(light green wire), and alternator is off so is a Ground(0volts)
Battery Light is ON

When you start the engine, alternator starts to generate power, about 14volts
Now one leg, that had 12volts, is now 14volts, and the other leg(green wire) at alternator is also 14volts, so bulb is OFF

If alternator voltage drops below battery voltage, say 8volts, then one leg has 12volts(battery volts) and the other leg 8volts so bulb is ON or flickering.

So fairly simple system.

Green wire is connected to internal voltage regulator
So failure of regulator could cut connection of the green wire, so not a Ground or low voltage, an open circuit.
But you would get no Battery Light ON with key on, indicating a problem with charging system

Battery Light circuit often has its own fuse, in 2002 Ranger that would be Fuse 11 7.5amp in cab fuse box, if that fuse blows you would also have no Battery Light with key on, and alternator would not work either, Battery Light circuit is also the ON/OFF switch for alternator

After installing new alternator, turn on the key and make sure Battery Light comes on, if not check that fuse

 

[gw33gp]

Yes, I do remember the battery light coming on sometime when all the other quirky things started. The battery light was one of the later things to happen though. From what Ron said, it sounds like the voltage regulator went out. I replaced the entire alternator. It had almost 210K miles on it so it was due for replacement anyway.

There were no codes to clear but I think disconnecting the battery overnight took care of that. I know there was at least 1 code stored because the CEL came on. I forgot to check the codes before disconnecting the battery.

The strange thing is the CEL light came on again this morning on the way to work. This time the code indicated EGR excessive flow detected instead of insufficient flow like it did several times before. It looks like the DPFE sensor is bad. Pretty much everything else in the EGR system is working like it should.

So far, the charging system is operating as it should now. The voltage after startup seemed a little high and I will keep an eye on that.

 

[RonD]

Start up voltage should be between 14.5 and 15volts, recharge voltage

Maintenance voltage should be under 14volts, usually 13.6volts

DPFE sensor uses 2 hoses to the exhaust manifold and/or EGR tube
One is closer to the EGR valve and one farther away.
DPFE measures the pressure difference between these 2 hoses
If EGR valve is closed the pressure should be equal
If EGR valve is slightly open pressure will be less on the closer hose
If EGR valve is fully open there will be a larger pressure difference on the closer hose.

Problem with DPFE sensor setup is the same problem that happens in all exhaust systems, water.
Burning hydro-carbons(H-gasoline) with air(Oxygen) gives you a by-product of H2O(water)
This is why exhaust systems rust from the inside out and why water drips from the tail pipe, or steam comes out tail pipes in cold weather.

Water vapor condenses on colder surfaces, i.e. cold glass of beer on warm day gets wet on the outside.

The DPFE sensor and hoses cool down faster than exhaust pipes, so will get water condensing inside them.
This will kill the sensor over time but also clog the hoses.
So check the hoses to make sure they are clear and crack free.
You can check DPFE sensor with vacuum pump but if you live in a humid area and DPFE sensor is 5 years old it may just be time to replace it.

If you blow out the hoses once a year they should be fine for longer time.

 

[gw33gp]

The DPFE sensor is 14 years old and no maintenance has been done to the EGR system from day 1 when I bought the Ranger new. I live in the relatively dry area of SoCal.

The strange thing is when I have it on a performance tune, I get no CEL. It only happens when I am on the stock tune.

I have found a way to test the DPFE that measures the resistance across two of the pins. It is simpler than measuring the voltage. That should give me an indication if it is bad or not. I have applied vacuum directly to the EGR valve and the engine stumbled. So, it is opening and closing. I also applied 12V to the EGR vacuum control valve. Again, the engine stumbled to indicate it is working properly. The vacuum hoses and electrical lines all look good. The in coming voltage to the DPFE is 5V as it should be. The only thing left is the DPFE unit itself or the ECU which is unlikely. I will check the DPFE resistance and order a new one if it looks bad.

 

[RonD]

You got quite a few years out of that sensor, SoCal location might explain that time frame

 

[wildbill23c]

Will a failing alternator cause the lights to dim, heater fan speed to slow down, etc. when at idle? Or would that be a battery issue? This is on an 88 Bronco 2. Battery light isn't coming on or flickering, but the headlights, instrument lights, and heater fan speed slows way down once the vehicle has warmed up and is idling at a normal idle.

 

[RonD]

Will a failing alternator cause the lights to dim, heater fan speed to slow down, etc. when at idle? Or would that be a battery issue? This is on an 88 Bronco 2. Battery light isn't coming on or flickering, but the headlights, instrument lights, and heater fan speed slows way down once the vehicle has warmed up and is idling at a normal idle.

Yes, that would be the alternator, one of the fields has failed, it can be stuck voltage regulator but these usually fail outright, no voltage out of alternator

When engine is running the alternator should put out a minimum of 13.5volts
A battery has less than 13volts so all electrical power is running off the alternator, and the slightly higher voltage from alternator keeps the battery charged.

A 100amp alternator doesn't have 100amps available all the time, usually that rating is max amps with engine RPMs at 2,000.
With engine at 700rpm a 100amp alternator might only have 60amps available
If you add high watt driving lights or a high watt sound system then you should also add a higher AMP alternator, or lights can dim at idle because you have gone over max AMPs available at low alternator RPM

An alternator has 3 "field coils" in it's case, the rotor gets 7 to 9 volts from voltage regulator, as the rotor spins that 7 to 9 volts creates a magnetic field in the alternators case, the 3 "field coils" generate AC voltage from that spinning magnetic field.
Each Field coil has 2 diodes that change the AC volts to DC volts
An alternator produces 13 to 15volts from the 7 to9 volts, it varies based on RPMs, and the voltage regulator raises and lowers the rotor voltage to compensate for RPMs AND Load, if you turn on the lights voltage will drop for a second until voltage regulator cranks up rotor voltage to get 13.5volts back.

If a field coil or its diodes fail then that field stops producing voltage, and while you do lose 1/3 of alternators max AMPS, the voltage regulator cranks up the rotor voltage to compensate for this loss
But at idle the alternator voltage will drop below 13.5volts, especially under higher load, i.e. lights and heater fan on
So you will notice that in dimming lights and slower fan.

But as you increase RPMs the alternator can generate minimum 13.5volts again so all is well.

It can run this way for a long while, as long as idling is kept to a minimum.
But shopping for a good deal on a new or used alternator would be a good idea

You can hook up a volt meter to the battery and watch voltage change as you raise or lower RPMs and add or lessen Load
Should always come back to 13.5volts, i.e. voltage will go up with RPMs but if you leave RPMs at say 2,000 voltage will go back to 13.5volt.
As lights are turned on voltage will drop then come back up to 13.5volts

At start up the battery was drained by starter motor, so voltage regulator will crank up rotor voltage to "recharge" drained battery, 14.5 to 15volts will be seen, that should only last a few minutes, that high a voltage will "cook" a 12volt battery if it constant.
The 13.5volts is a "maintenance charge", won't cook the battery just keep it charged for next start up