2000 XJ - Volt meter peaking, gauges jumping

I have a 2000 XJ 6.0 4wd. Lately, after driving for 5 minutes or so, the volt meter will jump to 19 volts and the gauges will jump all around, including the speedometer. The "check gauges" light will come on and my AC fan will "pulse" faster when the gauges jump around.

Is this the voltage regulator? Is it inside the alternator or outside? Also, my auto tranny will, occasionally, not downshift at all unless I do it manually. This started happening at the same time as the gauges freaking out. Could this all be due to a faulty computer?

I think the Voltage regulator is still in the ECM. This could have changed though.

It's best to start simple (and cheap) by checking your battery cables for tension and possible corrsosion.

The gauges on my 99XJ sometimes jump around and then they all go dead. I bang on the dash and they come back to life!! I've heard that it's due to a bad connection in the back of the console that can be taken apart and cleaned......

My headlights are also pulsing badly, as it turns out. Most people think the voltage regulator is in the ECU. If I bought a new alternator with an internal regulator, could I get away with not buying a new ECU?

Nope. Not on that one!!

It's externally regulated. The ECM does the controlling of the voltage.

If the brushes inside are going or the connection is dirty, that will cause your symptoms.....

Have someone run your codes, that will give you a defnate idea where to start. I haven't EVER seen a Mopar ECM fail yet. So start with getting the alternator tested.

steveybass said:

I have a 2000 XJ 6.0 4wd. Lately, after driving for 5 minutes or so, the volt meter will jump to 19 volts and the gauges will jump all around, including the speedometer. The "check gauges" light will come on and my AC fan will "pulse" faster when the gauges jump around.

Is this the voltage regulator? Is it inside the alternator or outside? Also, my auto tranny will, occasionally, not downshift at all unless I do it manually. This started happening at the same time as the gauges freaking out. Could this all be due to a faulty computer?

Click to expand...

Since this problem starts after 5 minutes or so of when the engine is started tells me that this could be a wiring problem.... When something warms up... there is an intermittent connection....
Ensure ALL battery, alternator and ground connections are clean and tight.... IF the ECM is receiving false information where it were reading low voltage due to a bad or dirty connection; the ECM would respond to increase the voltage. Then when the connection is regained; the voltage would be high and the ECM would have to respond to lower the voltage.

Thanks. I'll check all these things out and let you know.

Where are all the ground connections located?

Also, there are certain spots in my town where i drive that seem to cause all the crazy gauge-jumping and tranny-shifting. It seems like when i drive near powerlines, it causes it to happen. Is this possible? Regardless, it happens when i drive near the same spots every time.

As already suggested, begin with basic trouble shooting of the start and charge systems. Remove, clean, and firmly reconnect all the wires and cables to the battery, starter, and alternator. Look for corroded or damaged cables or connectors and replace as needed. Do the same for the grounding wires from the starter to engine block, and from the battery to the fender and engine to the Jeep's body at the firewall. Jeeps do not tolerate low voltage or poor grounds and the ECM/ECU computer may behave oddly until you remedy this. Check all the wire harness connectors your can find and make sure they are securely connected, especially the ones at the engine computer near the air cleaner.

Have the battery and alternator load tested for proper voltage and functioning at an auto repair shop or an auto parts store.

Thanks, Tim_MN.

steveybass said:

Also, there are certain spots in my town where i drive that seem to cause all the crazy gauge-jumping and tranny-shifting. It seems like when i drive near powerlines, it causes it to happen. Is this possible? Regardless, it happens when i drive near the same spots every time.

Click to expand...

Quite possible - if you have a CB and a linear amp, or a fairly high powered Ham radio, it will also happen every time you key up. It's due to bad quality grounds combined with the interference induced in the wiring by nearby power lines or high strength RF fields.

I don't have either of those.