Put in new alternator now engine idle is off and engine stalls

[Tim2003YukonXL]

I own a 2003 GMC Yukon XL 1500 4WD 5.3L and recently put in a new alternator. After installation I started the Yukon and noticed that the idle is not correct and the engine stalled. I drove the car around hoping that the computer would reset, but to no avail. I charged the battery overnight which seemed to solve the problem, but after running for 2-3 minutes the rough idle was back and stalled again. I brought the Yukon to my mechanic and ran a battery load test and the battery was fine. He hooked up his diagnostic and got no codes, other than not enough amps. Amps were all over the place, one second they were fine and the next they would drop and the engine would stall. Checked all connections and the wire plug on the top of the alternator appeared to be a little loose and clicked back into place and seemed to fix the problem.

I drove the car for 40 minutes at a variety of speeds hoping that this time the computer would reset and everything would be alright. I got home and let the car idle for 20 minutes with no problem. I thought that everything was alright, but by evening the rough idle was back and display lights were dim. This morning my wife drove the Yukon to work (less than 1 mile) and the car stalled.

I am not a mechanic so any help/suggestions would be greatly appreciated.

 

[Scottydoggs]

warranty the new alt. ive had this happen before, took 2 bad ones to get a third that worked. remans of course. but anything can be bad new in the box.

 

[OR VietVet]

First: Welcome to the forum from Oregon.

Second: The common denominator here is the new to rig alternator. I hate reman alternators and reman starters. Use one of these: https://www.rockauto.com/en/moreinfo.php?pk=3468318&cc=1415573&jsn=881

Also, make sure when you plug the new alternator in that the wires/pins in the plug itself do not push out backwards when you do plug in.


We recommend that you put all your rig(s) info in your signature so we all don’t have to guess at year, make, model, engine size, trans, rear axle locker…….etc. While you may have posted pertinent info in your first post, you may forget to do it again and the info is needed by us anyway. Makes it way easier on all members that attempt to help, to have that info right up front. It is also recommended that you take a pic of your RPO codes, on the inside cover of the glove box, and post that image in your signature. All this info will greatly help those that will try to help with a problem.


If there is any other info, like upgrades, mods or recent mechanical/maintenance work done, that would be helpful in any post as well. Too many times a question is asked by the poster and after about 10 responses we find out that the poster has done recent work to attempt to fix the problem or work that was done that SEEMS not related to the problem.

 

[S33k3r]

This is stupid, but I just did it to myself, so I figure worth mentioning. And, yes, before anyone comments, I was an idiot. That said, I did not properly reinstall my serpentine belt when I swapped out an alternator. I would assume, in your case, there would be some belt whine involved, so it is likely not that. But I figured it worth the mention. but like Scotty says, it is likely the replacement alternator is bad and needs to be replaced.

 

[Tim2003YukonXL]

This is stupid, but I just did it to myself, so I figure worth mentioning. And, yes, before anyone comments, I was an idiot. That said, I did not properly reinstall my serpentine belt when I swapped out an alternator. I would assume, in your case, there would be some belt whine involved, so it is likely not that. But I figured it worth the mention. but like Scotty says, it is likely the replacement alternator is bad and needs to be replaced.

Thank you for your suggestion - we have checked the belt and it is properly installed.

 

[Tim2003YukonXL]

warranty the new alt. ive had this happen before, took 2 bad ones to get a third that worked. remans of course. but anything can be bad new in the box.

This is what I suspected so thank you for suggesting swapping out the alternator. Will keep you posted once it is done.