Grand Prix GXP battery charging issues


Shawn1112

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Buddy of mine owns a GP GXP, not sure what year iirc they only made them a couple of years. Anyway about 2 weeks ago car was dead, he replaced the battery as the battery was about 7yrs old. No he didnt have the old one checked, he isnt the brightest when it comes to cars but he tries. So every morning when he gets in the car for last 2 weeks, the battery gauge (digital) is at like 11.5, car fires right up and he said once he starts driving the gauge shoots up to 14.2 or so. Well yesterday that didnt happen, car fired up and as he was driving to the expressway, the battery gauge stayed at 11.5. Brought it home and took his Wifes car to work. When he got home yesterday, he fired it up and took a ride and again it stayed at 11.5.

I'm going to go over there after work and try and diagnose it for him. I'm thinking bad alternator, so bringing my multi meter with me. Now iirc isnt the alternator on those cars buried and a PITA to get too? Anything else I should look at, not sure if these cars had common issues with the charging system.
 

lastls1

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Check the alternator first if course. However I’m pretty sure these cars had a BCM known issue that caused this? Way back when in college this was a “bug” the Instructors put on our shop Grand Prix. Everything checked out, except one of the pins on the BCM was not sending the proper voltage.
 
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Shawn1112

Shawn1112

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I recall the alternator is right on top.
Maybe I'm thinking of the tensioner being a PITA to get to? I remember helping someone do an alternator on one of these years ago.
Something was a PITA to get to, iirc we had to take one of the front wheels off
 

1quick

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Maybe I'm thinking of the tensioner being a PITA to get to? I remember helping someone do an alternator on one of these years ago.
Something was a PITA to get to, iirc we had to take one of the front wheels off
If it’s like the 3.8 version the power steering pump is buried and a pain in the ass
 

boostedguy05

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Alternator even on the 5.3 is passenger side on the top. If he has a tower brace you have to remove that but it should be an easy r&r
 
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Shawn1112

Shawn1112

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Stopped by his house and battery is not being charged by the alternator while car is running. Yes alternator is up top, 4 bolts look to be easy to get too. However the tensioner is buried and looks to be a major PITA as I suspected. Also I'm thinking when the alternator is removed, I need to tie that belt up so it doesnt slip off any other pullies. If belt comes off there is like no room at all to get your hands in there and get it back on.
 

CMNTMXR57

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There are two methods to remove the belt on a 5.3L

One is to obtain the proper Kent Moore tool (EN-47988);



I have one, but you would have to come get it.

The other option, and you may want to go look on the intertubez for specific instruction, but it involves a 4" hose clamp, removal of the passenger wheel, wrapping that hose clamp around tensioner and tensioner spring, and tightening the clamp. That might be a time consuming thing though. With that Kent Moore tool it's a 2 minute job. It is tight and a PITA, but it works.

Here it is in my 5.3;


But back on diagnosis. You really need to hook the battery up to a load tester, and see if under load that it's got sufficient amperage.

With the ignition off, it should read 12 volts (static voltage, not loaded). If so and it passed the load test, the battery is probably ok. With it running, if you're not getting 12-15 volts, that is indicative of the alternator is the problem.
 
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Shawn1112

Shawn1112

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There are two methods to remove the belt on a 5.3L

One is to obtain the proper Kent Moore tool (EN-47988);



I have one, but you would have to come get it.

The other option, and you may want to go look on the intertubez for specific instruction, but it involves a 4" hose clamp, removal of the passenger wheel, wrapping that hose clamp around tensioner and tensioner spring, and tightening the clamp. That might be a time consuming thing though. With that Kent Moore tool it's a 2 minute job. It is tight and a PITA, but it works.

Here it is in my 5.3;


But back on diagnosis. You really need to hook the battery up to a load tester, and see if under load that it's got sufficient amperage.

With the ignition off, it should read 12 volts (static voltage, not loaded). If so and it passed the load test, the battery is probably ok. With it running, if you're not getting 12-15 volts, that is indicative of the alternator is the problem.
We did the clamp on the tensioner (thanks youtube), took the 2 of us a little over a hour this morning. Battery is now reading like 14.4 with car running.
So it appears that was the issue.
 

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