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Alternator


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I am getting closer to getting the MJ back on the road. I believe I need a new alternator. I can crank it up, but if I remove the battery cable it dies immediately. I drained one new battery already just letting it idle and run. The MJ hadn't been cranked in 4 years, so I wanted the oil to circulate and lube the engine.

 

Would you guys buy a new alternator (~$100) or try a used one from the JY ($30)?

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Don't yank the battery to test the alt, that trick went out of style with carbs. Doing that to an EFI rig with an engine computer is a great way to end up buying a new engine computer along with anything else containing electronics capable of emitting magic smoke.

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I appreciate all the advice. I guess I am used to doing things the old way and just taking off the cable. I put a voltmeter across the battery terminals to test the voltage. The battery voltage at rest was 12.45 V. The voltage at idle speed was 12.35V. I was expecting a voltage of around 14V with the engine at idle.

 

The positive cable to the starter isn't in the best shape. I am going to replace it tomorrow. I will take the alternator off and test it if I have time.

 

Did you know that Advance Auto is offering a $50 discount when you purchase $100 of parts online? A new alternator and a battery cable would qualify for the $100 and I would get a $50 coupon for the next $100 purchase. Not a bad deal for a Jeep owner. How many times do you go to the parts store and drop $100? I believe Advance is trying to promote their online purchasing system to compete with RockAuto.

 

I am going to look in my Jeep Service manual...but does anyone know a test for determining if it is the alternator vs. the regulator? A quick test with the multimeter might save me from pulling a perfectly good alternator.

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  • 2 weeks later...

I believe I am going to have some time today to pull that alternator. I would like to ask one more question about them. RockAuto and Advance both list options for higher amperage alternators. It seems the standard is 61 amps, but 85 and 100 amp alternators are available. The price is essentially the same for the higher amp alternators.

 

Is there any advantage to having the larger alternator? I don't plan on adding extra lights or anything that would demand a higher draw. I think I am going to order the standard 61 amp alternator. Thoughts?

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Go big or stay home. If the bigger is about the same price, I would go higher output. At least the 85 amp one. I need to upgrade my 2.5 alt as it barely keeps up with the blower motor and lights at the same time.

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