System Voltage Level Low?

Before I start, I know I need to get a volt meter (on the list fo things to buy) and actualy measure my voltage... that being said I have a system voltage question.

As unacurate and vauge the instrument cluster gauges are I think my Alternator may be on its way out or on the weak side. My voltage gauge has in center 14V which in past experiance between 14 to 14.5V is typical for the system voltage when the vehicle is running. My guage looks like its more on the 12V to 13V when running (regardless of what accessories are on or RPM of engine). Do Alternators generaly drop in voltage as they get old or are about to fail? or do they just stop working?

Other Items are over the last few weeks when I would try to start the Jeep the starter would engage the bendix but does not crank. I turn the key to acc, and then try to start again with out any wait and it starts fine... low voltage problem?

Thanks for any help. Looking to see at this point since I have not gotten an acurate system voltage level, if other's voltage gauge actualy shows they are getting 14V or if they in general all show running lower voltage.

I don't think there's any way around getting yourself a voltmeter to get this answer. Actually, you could go to AutoZone or any of those chains and they will put a charging analyzer on and tell you if it's battery, alternator, or both.

I would remove the cables and clean the terminals, check battery voltage with cables off or back on and clean. Then start the car and check the voltage with the car running, then the a/c, lights and blower motor on. See where the drop-off is.

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 and engine to the Jeep's frame/body. You must remove, scrape, and clean until shiny, the cable/wire ends, and whatever they bolt to. Jeeps do not tolerate low voltage, bad connections, or poor grounds.

The dashboard Voltage gauge may or may not be accurate, but it does properly reflect the status of your charging system. If it indicates low charging, or high charging, you have a fault that needs to be addressed.

As suggested, have the battery, starter, and alternator Load Tested.

The main power connections are all good, I have replaced all gounds and main power over the last few years to high strand 2 guage copper with soldered copper ends. Batery terminals are clean all free of corosion, and are solid copper gold plated terminal connectors (not to sure how the terminal to wire connections are...). Paint was removed at all body grounds with a dremmel. Guess Auto Zone will do all that stuff for free (the load testing) so guess its no $$ out of my pocket. Althought I have not had the best of luck from their machine... have had mixed results.

What is the "normal" system voltage on a healthy XJ? (Engine Running, AC off)

http://www.jeepforum.com/forum/f27/primary-battery-starter-alternator-electrical-testing-1171690/


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13.20VDC Battery, Engine RUNNING, Alternator CHARGING (min.)
15.00VDC Battery, Engine RUNNING, Alternator CHARGING (max.)

Magus2727 said:

My guage looks like its more on the 12V to 13V when running (regardless of what accessories are on or RPM of engine).

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My alternator did this, but used to get as low as 9V. I had it benched and rebuilt and the (rectifier?) diodes in it were failing. Now it runs at 14V if nothing is on, and 12V if the main cabin fan is running. Theres a thread about that issue somewhere.

Thanks, Guess all I neeed to do now is get a volt meter I can trust... and test my Jeep. So it sounds like the rectifier failing might be a common thing...

My 2000 XJ runs at a little under 14v (13.5?) on the dash voltmeter all the time. I asked the same question when I first got it and the advice was that it was probably ok. I checked across the battery terminals and got about the same reading. Three months later all is well.

I'm not sure if the OBDll XJs are the same, but the earlier models had the volt gauge as the last instrument on an over-taxed circuit. It is notoriously inaccurate when many accessories are being used.

My '88 would dip below 9V at idle with the heater blower running. I assumed it was a bad blower, but the replacement didn't help. When checking at the battery (with the gauge reading 9-10) I consistently had 13-14V available.

I replaced the lighter with an aftermarket gauge driven by the lighter circuit and it now shows the true available current in the system

My worry is that the voltage may be to low when the blow motor is running at full and the Aux fan is on and the AC if running that I am getting to low of voltage at my AC clutch after having some loss through the relays, and other sensors. I have taken it to many different shops, replaced a few sensors. The AC clutch still has moments where it does not engage. but if I turn the AC off and the blower fan way down for just a few seconds, and then turn the AC back on with the low blower speed I get cold air out... and then I can slowly turn up the blower.

I have checked the connection at the clutch and the gap at the clutch. When it was not engaging a shop checked the voltage on the line and read 11 volts. hit it with 12V and the clutch turned on.

So the first thing I am going to check before possibly doing a rewire will be to see if my over all system level is low.

Scorpion8 said:

My alternator did this, but used to get as low as 9V. I had it benched and rebuilt and the (rectifier?) diodes in it were failing. Now it runs at 14V if nothing is on, and 12V if the main cabin fan is running. Theres a thread about that issue somewhere.

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Did you rebuild it yourself? If so, where did you get the parts for it? I can't find a decent rebuild kit for my '91 denso alt. It's fine now, but I've owned the jeep for 6 years. Eventually, it's going to go.

There are auto (would not call them stores or even shops...) but places that will rebuild your starter will also most likely rebuild your alternator. Call your local part store and ask if they know where you can get an alternator rebuilt... they might know.

montanaman said:

Did you rebuild it yourself? If so, where did you get the parts for it? I can't find a decent rebuild kit for my '91 denso alt. It's fine now, but I've owned the jeep for 6 years. Eventually, it's going to go.

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As Magus above recommends, find an automotive electric shop. Guys there do almost nothing but starters and alternators, and if you get a good one he'll fix what needs fixing and not hit you for what doesn't. Getting my starter rebuilt locally turned out cheaper than a parts-store one rebuilt by some unknown factory with mystery parts.

You can still get good work for a good price from an American in your neighborhood. That's pretty cool when you think about it.

Yeah ... I was kind of hoping to do it myself. I've never done it before and would like to do it at least once ... a full bench rebuild, complete with full testing of all parts, etc.

Bearings and brushes are easy to find, but other parts are more difficult. Some day ... I'll put some time into trying to find a good online source, and when I do, I'll post it on naxja. The local rebuild shops must have a source ... it's out there somewhere, we just need to find it.

montanaman said:

Yeah ... I was kind of hoping to do it myself. I've never done it before and would like to do it at least once ... a full bench rebuild, complete with full testing of all parts, etc.

Bearings and brushes are easy to find, but other parts are more difficult. Some day ... I'll put some time into trying to find a good online source, and when I do, I'll post it on naxja. The local rebuild shops must have a source ... it's out there somewhere, we just need to find it.

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If you can find bearings and brushes, and if the slip rings aren't gouged up, you're probably OK to do that. Diodes don't wear out, just fail from time to time and rarely at that, so bearings and brushes and a good cleanup would probably put you back in action for a very long time assuming the alternator isn't shot to start with.