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Discussion Starter · #1 ·
I have an 89 Jeep Wrangler 2.5L 5-sp manual. Replaced the alternator with a 78 amp and now I don't get proper volts as measured at the dash gauge. It went from steady at 14 with the old one to more like 8-9 with the new. Things like wipers and blinkers are now slooooow. The old Delco-Remy alt supposedly rated at 56 amps. Battery is less than a year old, cables were just replaced with 2 gauge. I suspect I need to wire something differently(?) or do I have a defective alternator(?) I'd appreciate any thoughts on how best to test, and/or I'd welcome and knowledge regarding a higher amp alternator.
:beerme:
 

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'89 YJ 4.2 with MC-2150 Carb & HEI, 2-1/2" Ex. AX-15, NP231 SYE, Adams shafts, F&R ARB, 3
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Quick question, Where did you pick it up? New, Rebuilt, or junkyard
 

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Maybe incorrect wiring or bad alternator, 8-9 volts usually means it is running off the battery. Most autoparts stores can test an alternator for you either in the vehicle or out of the vehicle though removed is preferred.
 

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'89 YJ 4.2 with MC-2150 Carb & HEI, 2-1/2" Ex. AX-15, NP231 SYE, Adams shafts, F&R ARB, 3
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Welcome Steve YJ, Click on the FSM link in my signature below, Open the 89 FSM and scroll down to the Charging section starting on pg 1400. There are Cherokee models included so look for the YJ specific info and diagnostics. May help you solve your problem.

I'm not an electrical engineer like some of the guys here, but my quick check to see if the alternator is working is to check the battery voltage with the key off, Then start it up and check it running, depending on the condition of the battery, I usually see a volt or more bump. ie; 12.5 to 13.9 on my 89 last time I checked.
 

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'89 YJ 4.2 with MC-2150 Carb & HEI, 2-1/2" Ex. AX-15, NP231 SYE, Adams shafts, F&R ARB, 3
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Thanks. I'll test and report back. It's a rebuilt alternator - "Driveworks" from Advance Auto - not much choice for me around town.
I'd take it back and go through local Napa if an option for you, otherwise go online. I gave up on Autozone for anything except minor parts.
 

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Discussion Starter · #7 ·
12.3v initial reading; 11.9 at idle with no load; 11.5 with lights, radio, heater.

This rig is all stock, besides a basic stereo (no amp) there is little more difference on the load. From reading I understand that a higher amp alternator may need an increase at idle speed to change. 56 to 78 amp doesn't seem a huge leap. Am I missing something? Voltage regulator? Is it a defective alternator? I can take it out again to bring to the store today but we're in the middle of snowstorm Eleanor lol and I need the Jeep to get there!
 

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'89 YJ 4.2 with MC-2150 Carb & HEI, 2-1/2" Ex. AX-15, NP231 SYE, Adams shafts, F&R ARB, 3
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You are running off the battery, alternator is no good, or you have a faulty wiring connection
 

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Discussion Starter · #10 ·
So, yep - bad alternator. I put the old one on and everything was ok (except the squeal) - took the new back and had them test it and they had indeed given me a bad remanufactured piece. I have time - the old charges, just not well. I'll look online for a better one. Thanks to all for your feedback and suggestions!
 

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Welcome to the Forum Steve YJ,

It sounds like you've found the problem and are on track to a cure.

Good Luck, L.M.
 
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