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As if things couldn’t get worse

Club31XJ

NAXJA Forum User
Location
Canyon Lake
Ok guys so I’ve posted a couple different threads here pertaining to my 1991 4.0 jeep xj. My first issue was not getting spark. Found that the problem was a faulty pcm. During the process though I replaced a boat load of part. Starter, alternator, battery, spark plugs and wires, coil, distributor, and also pcm. Finally got it all started and was running fine for about 40 miles. Then noticed a check engine light came one and my battery voltage was way low. The check codes it threw were 34,41,21 and 62. I figured out the 34 code (map sensors vavcuum hose was clogged. 62 says it’s not reading my odometer and the 41 is the alternator is not charging the battery but as I stated before it’s brand new. So I have no idea what my problem is. The pcm is an A1 Cardone which I ordered online. I didn’t have the original serial sticker number from the old one because there was no sticker on it. So I put in online the type of vehicle I had assuming it would be the correct one. Everything was working fine except now I’m getting this 41 code and the alternator is not charging. What in the holy hell is going on?


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How tight is the belt?
 
If the belt and wires to the alt are good, then the pcm is bad. Alternator voltage is controlled through the pcm,

Of course the alternator could be faulty, you could have it tested, if the belts and wires are good. But if it’s good and everything else is as well then the pcm is bad.

A1 used to be a better name, but they easily could have sold a faulty pcm.


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in the kit i see the field replacement module used to trick the computer from throwing a code is this a resistor? i ordered mine from rock auto with wire harness for under 20$
 
I thought that maybe some important information of something that I have found out is that when the engine is cold the alternator seems to be working but as soon as I get up to operating temperature it throws the code 41 and the alternator stops working. I was going to try and run some test with the ohm meter to see if there might be a short in the circuit somewhere.


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Slightly loose connection that's opening up as things warm up and expand?
 
Just saying that the alternator is new doesn't mean that it's charging. Have you verified the battery voltage? It should read about 13.2 at idle. If it's not reading that, it could be as simple as a bad ground wire.
 
in the kit i see the field replacement module used to trick the computer from throwing a code is this a resistor? i ordered mine from rock auto with wire harness for under 20$


Looks like it. Probably just to put a load across the lines from the computer so it doesn't think it's an open or shorted circuit. Although, I'd suggest that if it works to avoid the trouble code, then the PCM is likely to be able to control the alternator field coil by itself and you don't need an external regulator. $20 for a $2 resistor seems a bit high on the markup.


Have you measured the voltage across the field terminals when it's failing to charge? That'll tell you if the problem is the alternator or the pcm/wiring. Disconnecting the wire from the computer and putting full voltage across the field coil should also tell you if its the alternator not charging as well.
 
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