Was driving yesterday and noticed my "check gauges" light was on. Saw that the alternator gauge was setting on zero. Three hours later I drove home (about 20 miles) and, after less than a mile into the trip, the gauge dropped to zero. Made it home fine. Jeep cranked easily after I got home. Cranked easily this morning. Drove about 20 miles around the neighborhood and on the highway and gauge registered one peg south of 14 except a couple of times it dropped to 2 pegs south of 14. Put volt meter on battery terminals and showed 12.5 with lights on and ac running. With lights and ac off and motor running shows 13.5. Battery shows 12.9 with engine off. Anybody have an idea what happened yesterday?
At high idle with nothing else running, you should see approximately 13.5 to 14.4 volts at high idle measure at the battery. What I would try first is freshening all engine grounds and see if that helps. If it doesn't, you are likely on the front end of an alternator failure. Good luck!
Grounds can be the root cause of many electrical gremlins. Refreshing grounds is NEVER a bad idea, and the investment of your time in this procedure is always well worth it!
You can't tell much of anything by looking at ground connections!! You must remove, scrape, clean until shiny the cable/wire ends and whatever they bolt to. Be sure to remove all paint from any ground connections.
Start with the one on the back corner of the head, and where it attaches to the firewall, as it deteriorates over time and is an area that makes it susceptible to damage. Best to replace that woven cable with a #4 or #2 gauge cable. You can attach the one end to the intake manifold if you would like.
Next go over to the engine dipstick tube stud. Remove the nut and clean the wire ends and scrape the block until shiny at the stud. Reattach tightly.
If you are so inclined, add at least a #6 cable from the negative terminal of your battery to one of the bolts on your radiator support.
99 Cherokee, 4.0 AW4, NP242
Past Jeeps: 49 Willys, 81 Scrambler, 88 Comanche Without "data", all you have is an opinion!
Removed alternator and took to advance auto for testing. Parts personnel ran test and alternator checked good. He repeated test three more times and all checked good. I had removed battery previously and placed on charger. When I attached leads, battery immediately showed 100%. This was after driving car approximately 40 miles with ac operating and part of the time with lights and radio on. Doesn't it seem that if the alternator wasn't working that the battery would be discharged at least slightly? Don't mind replacing parts, but only if they are defective. I noticed two grounds visible from under the hood--one off the battery grounded to the inside fender and one to the inside firewall, which I assume is the main ground. I know the starter has one. Are there others? Also, has anyone has a bad gauge problem with this vehicle? Thanks.
Do all the other gauges work? Have you done the gauge test? Depress the odometer reset and turn the key to run. The gauges will all cycle and all the lights will activate. The gauges are digitally controlled. Each sending unit goes to the PCM where it is digitized and sent to the dash. The "sending unit" for the voltmeter is in the PCM. When my PCM failed, the voltmeter just moved off the 9, but the check gauge light didn't come on.
Alternator gauge failed again today. Checked voltage at battery with ac running and checked 13.35 volts. After car sat for 20 minutes, gauge started working again. Checked voltage at battery with gauge showing just shy of 14 volts and checked 13.30. Turned ac off and checked 13.35. Will try gauge reset. Wonder what is going on?
Just reset gauges. Noticed alternator gauge was showing a little low after cranking. Checked volts at battery and checked just over 12 volts. Mmmmm. Noticed that engine was not running as smoothly as before. Then engine smoothed out and volt meter jumped to 13.35. Looked at gauge and it had also jumped up to just shy of 14 volts. Believe alternator is in early stages of failure. Any ideas on further verifying this?
Just because an alternator checks good on a test machine, does not always mean that it is good.
Perform routine maintenance 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. Copper wires should be copper color, not black or green. Do the same for the grounding wires from the starter to engine block, the ground wires at the coil, and the ground wires from the battery and engine to the Jeep's frame/body. You must remove, scrub clean until shiny the cable/wire ends, and whatever they bolt to. Jeeps do not tolerate low voltage, bad connections, or poor grounds.
Place your DVOM (Digital Volt Ohm Multi-Meter) on the 20 volt scale. First check battery voltage by placing your multi-meter's positive lead on the battery's positive post ( the actual post, not the clamp ) and the negative lead on the negative post. You need a minimum of 12 volts to continue testing.Next, leave your meter connected and take a reading while the engine is cranking. Record this voltage reading. Now connect your positive lead to the battery terminal stud on the starter and the negative lead to the starter housing. Again, crank the engine and record the voltage reading. If the voltage reading at the starter is not within 1 volt of battery voltage then you have excessive voltage drop in the starter circuit.
Typical voltage drop maximums:
• starter circuit (including starter solenoid) = 0.60 volt
• battery post to battery terminal end = zero volts
• battery main cable (measured end to end) 0.20 volt
• starter solenoid = 0.20 volt
• battery negative post to alternator metal frame = 0.20 volt
• negative main cable to engine block = 0.20 volt
• negative battery post to starter metal frame = 0.30
• battery positive post to alternator b+stud = 0.5 volt with maximum charging load applied (all accessories turned on)
Test the output at the alternator with your volts/ohms multi-meter. You should be measuring 13.8-14.4 volts.
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Is there an easier way to find out if I have a bad alternator. I like playing around with cars, but at age 66, with arthritis and other aches and pains, I won't be able to do all of those checks. I can see it now...."well, ace , I ran all those checks you wanted me to run and...guess what...you have a bad alternator. Here's your bill...$150 for the alternator and $300 for those checks that verified it". No thanks.
No there is no easy way to test it. When the voltmeter drops the car runs poorly and your DVM reads low. All of the those items point to low voltage causing the problem. The regulator is in the PCM, if you have access to an O'scope you could test it. Of course you have to have it connected when the car is acting up. I won't go into all the details on the regulator, but typically once a transistor/IC/diode fails they don't heal themselves, they stay broke. Alternators on the other hand, do have a tendency to work and then fail, just as you describe.
I'm several months shy of you, and I feel your pain.
Seems like the alternator is on its way out to me as well. I had VERY similar issues with the gauges and specifically the "check gauges" light about a month ago. Autozone also tested the alternator good even though I knew it wasnt.
Replaced it and havent had an issue since. I also fixed some wires that could have been the cause or added to the cause at the same time...
check my post here and your wires in similar locations