Recently my 93 xj has been having a problem with alternator output. Sometimes but not all the time, when i start it up in the morning or to leave from work in the evening after its sat all day, the alternator output is only about 11 v, sometimes setting off a check engine light. Then after about 20 to 45 seconds, it just decides to kick back up to normal, around 14, 15V. If i shut it off and start it right back up, the voltage stays at normal and the CE light goes off. I verified with my dmm that the output is true with the dash gauge reading. I also checked the voltage drop across the the alt. to batt. cable and it was fairly low.

So im guessing the voltage regulator, which of course is internal, is on the fritz and I need to replace the alternator. Im just wondering if this is the best guess or if there are any other troubleshooting tips i might have overlooked or other possible causes of this issue.

???
thanks

 

I think it's more likely that the alternator is heading south, not the voltage regulator.

 

Check your grounds just to be safe but it sounds like your alternator is dying.

 

I'm not sure what you mean by the voltage regulator is internal but just to be clear, the regulator on the '93 is in the PCM, not the alternator.

I agree that it is probably the alt and not the regulator.

 

This is correct! And it isn't very common for them to go bad. Like every one else side. More then likely it the alt. Pull it and have it bench tested at your local parts store.

 

Sounds like your battery isn't holding a charge to me. Let it sit overnight and check it with a multimeter. Parts stores will also do load testing

 

mine started doing this after i hooked up two batteries for a dual battery setup. I think i might have fried the comp hooking up the two batteries. (I am not an idiot they were parallel not in series so still only 12v) I think it might have been to much amps and fried the pcm. but mine does EXACTLY what your are describing. I haven't had the time to dive into it since 2 weeks into driving my jeep with the new crate motor the trans started slipping. when i pull it all back out to put a new trans in I will test the alt to see if that is it or rule it out. Mine is doing the exact same thing so I hope for both of us it is just the alt.

 

Electrical devices draw only the current that they need so having additional amps available in and of itself will not harm the PCM.

 

that was my theory behind putting my batteries in. but when I first started it up It acted exactly like greenmachine stated so i unhooked one battery thinking I fried something. still haven't fully explored the alt tho.

 

Im just gonna throw a new alt in it. I was thinking this type alt had an internal voltage regulator i didn't know it was pcm regulated. And I doubt its a battery problem i recently had it load tested and it was good. And if it was just a batt problem then the alt should be putting out too much voltage not too little.

 

Ah good to hear it's load tested. And you wouldn't be able to tell the voltage that the alternator is actually generating without disconnecting the battery from the system, which means the PCM doesn't have any sane/regulated reference supply, which will burn itself out since the internal VR can't quite work properly. Low voltage in the whole system can simply be caused by a battery drawing way too much current like if you left your lights on all night.

 

any updates? I checked my alt and battery and both came out fine. and last weekend my computer started making this high pitched noise which some people on here have said is the "death squeal". that a capacitor has overloaded and my computer is about to fail. I just wanted to know if you had fixed your problem since mine was doing exactly what yours was doing.

 

Yeah im sorry to keep ya hanging i posted an update from my phone like 2 weeks ago i guess it didnt send. Yeah it was kind of pain in the @$s, mainly cause of the ac lines near it, but i got the new alt and belt in and its charging perfectly now. One other thing i noticed within the past couple weeks is that the voltage was tending to run on the high side. I noticed my glovebox latch tends to stay open just enough to keep the light inside it on- parasitic load, so i just unhooked the connector and that fixed that, voltage is fine now.