Voltage fluctuates while driving; "check gauges"

[matkal]

Check gauges light came on and voltage was down to half way between red and 14v. I pulled over, left the engine running and popped the hood, all appears normal. Read a couple threads on here describing the same condition and had the alternator checked at Napa and O'riellys both said it's good. I checked connections at battery, grounds, alt, etc. all were good. Checked voltage across battery and from battery to alt; same readings, which are 12.2 w/eng off and 11.6 running. Pic shows gauge reading. Pulled alt and forgot to check voltage between eng ground and alt. I plan on taking it to an alternator shop and have him test it hoping he will do a more thorough check.

The CEL never lit up.

Thoughts? Should I check voltage between engine ground and alternator?

 

[matkal]

 

[CharlesHS]

Remove the ECU 32 pin wiring harness connectors and inspect the clips and pins for oxidation.
The ECU controls the alternator charging rate of the battery and to the electronics.
Once you have confirmed the harness connectors condition; you can move on to checking the battery cables internal copper strands for oxidation,
Trace the wiring from the alternator charging stud to the battery and inspect the cables internal copper strands for oxidation.
Remove the cover of the PDC (fuse box in engine compartment); with the engine running check the incoming voltage of the power cable from the alternator to PDC power stud.
There is more testing that can be done, but these tests will provide you with what direction to go .

 

[matkal]

Remove the ECU 32 pin wiring harness connectors and inspect the clips and pins for oxidation.
The ECU controls the alternator charging rate of the battery and to the electronics.
Once you have confirmed the harness connectors condition; you can move on to checking the battery cables internal copper strands for oxidation,
Trace the wiring from the alternator charging stud to the battery and inspect the cables internal copper strands for oxidation.
Remove the cover of the PDC (fuse box in engine compartment); with the engine running check the incoming voltage of the power cable from the alternator to PDC power stud.
There is more testing that can be done, but these tests will provide you with what direction to go .

Voltage is 11.53 across all combinations: batt negative to pdc, batt positive and at the alt. Same using firewall ground and engine ground. Gauge reading is the same

 

[CharlesHS]

Voltage is 11.53 across all combinations: batt negative to pdc, batt positive and at the alt. Same using firewall ground and engine ground. Gauge reading is the same

All of that testing and results were found with the Jeep running ....
I just reread your earlier posts and if the voltage is 11.6 with the engine running, all cables and connections have been tested and the alternator has been tested at two AP stores then the problem is either the ECU charging circuit... or the battery has an intermittent problem.
I think I would have the alternator tested at another AP store just to ensure the findings of the other two stores.

 

[matkal]

All of that testing and results were found with the Jeep running ....
I just reread your earlier posts and if the voltage is 11.6 with the engine running, all cables and connections have been tested and the alternator has been tested at two AP stores then the problem is either the ECU charging circuit... or the battery has an intermittent problem.
I think I would have the alternator tested at another AP store just to ensure the findings of the other two stores.

Yes, all tests with engine running. Taking it to a motor/alternator shop tomorrow. I just sent my ECM to wranglerfix trying to diagnose a crank/ no start issue

 

[matkal]

Alternator tested good, ordering one of these
https://store.alternatorparts.com/h...gulator-conversion-field-replacement-kit.aspx

 

[matkal]

I installed the regulator bypass and I’m pretty sure it’s working as it should. I’ve never really paid much attention to my voltage gauge so I’m not sure how it should read when charging.

Battery was at about 11.5 before bypass surgery. Now it fluctuates between 14.5 and 15.1 with a volt meter, battery is at 12.66 (with engine off) after running/driving for a while.

Does this sound ok?

 

[sab]

That seems about right.

 

[matkal]

The fluctuating voltage is bugging the crap out of me so I called the guy I bought the kit from and he said to temporarily power the relay directly from the battery, if that solves the problem power it through a relay.
Well, that eliminated the fluctuating voltage. My question is, why does that solve the problem? I'm using a 10 amp circuit which is plenty to run the regulator.

 

[sab]

matkal:

I'm having trouble understanding how it WAS wired, and how he's suggesting to wire it. I went to the website to look for a wiring diagram and didn't see one. Did you get a diagram/instructions with it? If so, post a pic here, and I'll try to decipher it.

 

[matkal]

One pic shows the install WITH a relay, I did not hook up a relay. Yet

 

[matkal]

This is the “ relay kit”

 

[sab]

So here's what I see you're doing with the relay:

The field coil on the alternator and the new regulator is fed by battery voltage. In your original configuration, you supplied that by splicing to some switched ignition wire. However, the wire you spliced to can't handle the current requirements of the additional loads from the regulator and alternator field coil. As a result, the voltage drop is too much and the alternator's field coil and the new regulator are seeing a voltage that's lower than the actual output of the alternator (and instantaneous battery voltage). I don't understand exactly what's happening inside the regulator, but my guess is that this voltage drop causes it to fluctuate the alternator's output voltage because it thinks the output is lower than it actually is. So, it cuts off, then on, then off, etc., as it tries to stabilize something that it can't stabilize.

By using the switched ignition to switch a relay, you are now supplying a voltage to the alternator's field coil and the regulator that doesn't have a significant voltage drop because the wires on that relay kit are much larger. Now, the regulator, alternator field coil, and battery are all running at voltages that are the same (or practically the same).

 

[matkal]

Well I hooked the relay as shown, with the exception of the battery connection that I connected to the fuse box lug instead. No fluctuation but it stays at 11.6 volts at the battery. Adjusting the regulator has no effect on the voltage.

Rather than spending $50(!) dollars on a relay kit I used a relay I already had.

At this point I’m frustrated with this thing and have to walk away. I’ll triple check everything when I get a chance. Thankfully I didn’t do a permanent/neat hook up, just basically a mockup with longer wire than necessary and didn’t mount the relay.

 

[matkal]

It’s finally finished Solved the volt fluctuations by adding a relay rather than tapping into a switched circuit.

To diagnose the voltage fluctuation I powered the regulator directly from the battery and that solved the problem.

 

[sab]

"I love it when a plan comes together!"
-John "Hannibal'" Smith, 1983