How do I test the alternator and ECM to see if either is failing?

[Walkerman]

97 Wrangler Sahara:
For several months the volt gauge would go way down at idle but would go back up if I raised the rpms. A friend told me it was probably a bad diode. Driving yesterday the volts dropped all the way to the bottom. When I got home and turned it off and restarted it the volts went back up but after a few seconds the volts went back to the bottom again. I put a volt meter on the battery. It read 12v. I started it up and the volts showed it was charging but dropped off after a few seconds. I understand the voltage regulator is in the ecm. How do I check which is bad, the alternator or the cem??

 

[AndyG]

@Wranglerfix knows the electrical side very well- the @ symbol notifies him.

His forte is the 05-06 models but he will help if he can.

 

[Chris]

I agree, I would have @Wranglerfix test the PCM for you. He is the PCM expert and he's one hell of a great guy to deal with.

 

[tworley]

When my volt meter went haywire, my battery terminals were full of acidic buildup.

 

[WestCoastDan]

Is the belt tight? Is it possibly slipping?

You can likely remove the alternator and have it tested at a local parts store for free.

 

[Wranglerfix]

@Walkerman my office is in Davie if you’d like to drop it off to me for testing. The voltage regulator is inside that ECM and as long as it does not smell like burnt popcorn, it is generally repairable.

 

[Walkerman]

@Wranglerfix How do I contact you?

 

[Wranglerfix]

My telephone number is 866-888-7710.

 

[Walkerman]

Thanks for the help.
Wrangler fix only works on PCMs and you have to remove and bring it to them.
I am looking for info on what to do to determine which is bad. The alt. or the PCM.

 

[Rickyd]

Thanks for the help.
Wrangler fix only works on PCMs and you have to remove and bring it to them.
I am looking for info on what to do to determine which is bad. The alt. or the PCM.

As already said. You can have your alternator tested for free. If it is good then the only thing you have left is harness/wiring//ground issues or the pcm. If troubleshooting the wiring is beyond you then a shop can do it. If the pcm is in doubt send it to wranglerfix.

Look in thre resources section here for downloadable factory service manuals. They will help with diagnosis.

 

[Walkerman]

As already said. You can have your alternator tested for free. If it is good then the only thing you have left is harness/wiring//ground issues or the pcm. If troubleshooting the wiring is beyond you then a shop can do it. If the pcm is in doubt send it to wranglerfix.

Look in thre resources section here for downloadable factory service manuals. They will help with diagnosis.

Can the alt. be tested without removing it?

 

[TJ Jim]

Can the alt. be tested without removing it?

How many volts is it outputting? Do you have a multimeter? 14vdc indicates good. Less means bad. Of course the pcm tells it to charge at what voltage so that still leaves you with one of the two might be bad. So take it out and take it to the parts store and have them test it for best results.

 

[Walkerman]

How many volts is it outputting? Do you have a multimeter? 14vdc indicates good. Less means bad. Of course the pcm tells it to charge at what voltage so that still leaves you with one of the two might be bad. So take it out and take it to the parts store and have them test it for best results.

Upon starting engine it charges fine for 30-45 seconds and then volts drop to ZERO. It's really hard to take out. All my Advanced auto parts store has is a battery load tester.

 

[WestCoastDan]

Upon starting engine it charges fine for 30-45 seconds and then volts drop to ZERO. It's really hard to take out. All my Advanced auto parts store has is a battery load tester.

This is not meaningful information as it does not direct one towards a root cause. It could still be either the alternator itself or some other root cause.

I'm not trying to piss on you, but if you really think that pulling, testing & either replacing or re-installing the original alternator (to check it properly) is too much effort, then perhaps you should just pay someone to fix it for you.

 

[Walkerman]

This is not meaningful information as it does not direct one towards a root cause. It could still be either the alternator itself or some other root cause.

I'm not trying to piss on you, but if you really think that pulling, testing & either replacing or re-installing the original alternator (to check it properly) is too much effort, then perhaps you should just pay someone to fix it for you.

I have always done my own repairs but now at 80 years old I have to pay to get the work done. That is why I am trying to get all the info on tests that I could do myself. Thanks for your help.

 

[macleanflood]

My guess is that the Jeep is in closed loop and the PCM defaults to exciting the alternator. Soon as the PCM switches to open loop it shuts down charging.

But as stated...you need to pull the alternator and get it tested. You need to ohm out and continuity check the wiring. And if those come out good then you need to pull the PCM and send it in for testing. I'd also test your battery and clean the terminals and all the grounds.

-Mac

 

[Walkerman]

My guess is that the Jeep is in closed loop and the PCM defaults to exciting the alternator. Soon as the PCM switches to open loop it shuts down charging.

But as stated...you need to pull the alternator and get it tested. You need to ohm out and continuity check the wiring. And if those come out good then you need to pull the PCM and send it in for testing. I'd also test your battery and clean the terminals and all the grounds.

-Mac

Thank You.. Rick

 

[Walkerman]

How long should it take to replace the alternator on this 1997 Jeep Wrangler Sahara with AC??

 

[macleanflood]

How long should it take to replace the alternator on this 1997 Jeep Wrangler Sahara with AC??

20 minutes if you've done it once or thrice.

-Mac

 

[Steel City 06]

How long should it take to replace the alternator on this 1997 Jeep Wrangler Sahara with AC??

Very quick. Take a look at the Durango alternator modification if you have a lot of electronics or a winch. Basically a bolt-on modification that boosts you from 90 or 110 amps to 160+.