High Voltage at Kickdown/High RPM.

[Crowde]

Hopefully this isn't a duplicate. I did my best to search around first and found some threads with similar issues, but nothing quite the same.

The vehicle: 2003 Liberty Limited 3.7L 4WD, 216K miles.

Recently I've been having an issue where kickdown causes my voltage to spike from ~13.7v up to ~18v. Among the other dangers to battery and electronics, this causes the instrument cluster to go wonky, requiring a cluster exerciser test to fix.

So far kickdown is the only thing I've found that's causing the voltage spike to happen.

Symptoms/Info:

1) Only happens at kickdown (that I've experienced, at least).
2) Immediately returns to normal voltage when backing off the throttle.
3) No CEL, Battery Light, or Fault Codes on my ODB reader.
4) Possibly louder-than-normal whine at kickdown.
5) Possibly running very slightly rougher overall.
6) It has been HOT lately (~110°F).
7) I checked the fusible link between alternator and POS battery connector and have continuity.
8) Removed, contact cleaned, and replaced both the fusible link and the 2-pin connector on the alternator.
9) 2-pin-to-PCM wiring and connector seems to be in good shape, but I haven't had a chance to take a multimeter to it yet.
10) In the same timeframe this began happening, the water pump developed a small leak, with evidence of small amounts of coolant being sprayed around the engine bay.
11) There is a bit more grime buildup within the immediate vicinity of the alternator. It does not seem to have any scent, either oil or coolant.

Normally with a voltage regulation issue I'd suspect it's the PCM, as I understand that to be what's doing the actual regulation.

However I think I'm leaning alternator when looking at the overall symptom list. Between the louder whine, the possible increase in NVH, the wiring and connectors seemingly being ok, coolant, grime, etc. Would issues with the alternator be capable of overriding the PCM's voltage regulation?

I've also heard that the battery temperature sensor can cause voltage issues?

Any help in deducing the culprit would be greatly appreciated. I'm really hoping to avoid the costs of replacing the wrong part.

Thanks.

 

[Billwill]

Battery Temp Sensor does not do too much but you can remove it and put an Ohm Meter on it.

Then heat it up a bit by placing the Sensor on a light bulb......you should see the resistance changing as it heats up!

Been there done that...newer KJs they stopped using the battery Sensor!

You need to check the wiring from the PCM to the Alternator to check for shorts to Ground or open circuits...I found plenty faults after my GF pranged my Export 2.5L CRD into a tree!

 

[Crowde]

I checked the battery temp sensor, as well as having the battery and alternator bench tested. I also checked the fusible link between the battery and alternator, as well as the wiring between the alternator between alternator and PCM. All checked fine.

At this point I'm working under the assumption that it's a bad PCM.

I'll update for future reference searches once I get around to finding/flashing/installing a PCM as to whether or not that was the fix.

 

[LibertyTC]

One was a double post that I had to remove, please continue...

 

[Ksat]

Not sure it'd be helpful, but I found this:

"The amount of DC current produced by the generator is controlled by EVR circuitry contained within the Powertrain Control Module (PCM). This circuitry is connected in series with the generators second rotor field terminal and its ground. Voltage is regulated by cycling the ground path to control the strength of the rotor magnetic field. The EVR circuitry monitors system line voltage (B+) and battery temperature (refer to Battery Temperature Sensor for more information). It then determines a target charging voltage. If sensed battery voltage is 0.5 volts or lower than the target voltage, the PCM grounds the field winding until sensed battery voltage is 0.5 volts above target voltage. A circuit in the PCM cycles the ground side of the generator field up to 100 times per second (100Hz), but has the capability to ground the field control wire 100% of the time (full field) to achieve the target voltage. If the charging rate cannot be monitored (limp-in), a duty cycle of 25% is used by the PCM in order to have some generator output. Also refer to Charging Operation for additional information."

Perhaps it might be helpful to disconnect the wires going to the PCM from the alternator and run jumper wires to it in their place, in case there is some break or high resistance issue with the existing ones.

If that doesn't help, you might be able dispense with the PCM control altogether by just throwing a pulse width generator in its place. This basically "dumbs down" your former smart alternator and tells it to just output a constant voltage irrespective of loads, battery temp and whatnot. Just like the alternator systems of 20+ years ago did. You dial in the output voltage you want it to be (say 14.4) by setting the correct pulse frequency/amplitude on the generator.

 

[KJowner]

I've has issues with earth's on old cars in the past, try a nice fat wire bolted between the block and the earth on the battery.