Saturday, January 11, 2014

GMC Envoy 4.2L Alternator Replacement.

I imagine if you have a Saab 9-7x, 2nd generation Olds Bravada, Chevy Trailblazer, Izuzu Ascender, or Buick Rainier with the Atlas 4.2 liter I6, this procedure will be the same. As always, with any car repair work, there is a risk of injury, death or property damage. Use common sense when working on any electrical or moving part and implement any and all safety gear or procedures at your disposal. Tie back long hair and secure loose clothing. Wear gloves and other protection to prevent cuts and scrapes on sharp parts. The fan and clutch are expensive if they break as a result of mishandling. The wire harness to the fan clutch is particularly vulnerable to being caught in the fan and broken, wrecking some very pricey parts. Use extreme care and do this and any other repairs at your own risk.
The GMC Envoy is a body on frame panel truck that seats five to seven people, and the XUV version sports a retractable roof and a mid gate along with a weird looking behind. These are available in two or four wheel drive which is much more common. The version we're working on today is a Four wheel drive, 2003 Envoy SLE with the garden variety body that seats five. It has about 166,000 miles as of this writing. It also has the Atlas 4.2L I-6, which also more common than the 5.3 liter V-8. My dad replaced the battery a few days ago because it was over four years old and died in the extreme cold this past week. The engine sputtered and stalled when the heater was switched on. I found the voltage to the battery with the engine on varied from zero to fourteen and a half volts, and despite an "ok" from AutoZone, it was time to replace the alternator. They admitted they couldn't test the voltage regulator, even though the same was installed inside the part. Thanks, NOT!
To replace this part, you'll need an hour to do this job. You'll need a serpentine belt tool, a ten and fifteen millimeter wrench and sockets with a breaker bar and socket wrench. You can also hook wrenches together to get more leverage, but a breaker bar will be better. A socket wrench will be mandatory to get the alternator bolts out of the alternator boss as these are extremely long.

The mount above the alternator has 4 bolts, with the fourth
underneath the mount screwed to the engine. This is the space you
have to get the alternator out.

Remove the belt from the alternator and if it's sketchy, now is the time to replace it. The guide for threading it is molded on the fan shroud. IF you're saving the belt, take the loop off the alternator pulley only. The next thing to do is remove the NEGATIVE battery cable. The upper mount pictured above needs to come off and the fifteen mm bolts will be a PITA to remove. Use a breaker bar to get the two front ones and underneath the mount off. The ten mm bolt just needs an ordinary socket.
There are three fifteen mm bolts holding the alternator directly to the engine; two are on top and one on the bottom. If you're careful, you can use a socket wrench to get these out without breaking the plastic fan. Just let the fan move freely as you carefully swing the wrench back and forth. Loosen all the bolt, then remove the bottom first and the top ones last. Unclip the voltage regular connector and remove the wire from the battery terminal with a ten mm wrench. Carefully wiggle the alternator out between the fan, shroud and air conditioning hoses. This part is big and heavy, so taking your time is critical. You can also remove the intake plenum, help on by two clamps and two ten mm bolts, and move the wire harness out of the way to help out. However, this will only get you a minimum of clearance. You could also remove the fan and shroud, but this will add an hour to the job.

I would suggest making sure the battery is fully charged before putting the new alternator in service as this is not designed to change the battery per se. The alternator provides electricity to run the accessories, including the heater, seat warmers and other technical wizardry as needed while topping off the battery. It is not designed to charge the battery on a modern vehicle. You need to disconnect the battery on BOTH SIDES to charge it or you may fry the electrical system. Installing the part is the reverse of removal, but make sure the belt is seated on the pulleys and the tensioner retracts and moves freely. Again, if this or the belt are sketchy, they need replacement. When you start your truck, the engine will idle weird for the first time. Take a look at your work and make sure the tensioner holds steady and doesn't bounce. Also run the heater, lights and other accessories; the idle should not change any appreciable amount, nor the charging gauge change a whole lot.
Road test your truck and you're done. Maranatha!


Unknown said...

I have a Trailblazer with the 4.2L I6! It has over 170,000 miles on it and still runs strong. I haven't had to replace the alternator yet, but I figure that one day I'll have to do it. Thanks for the tutorial, I wasn't sure what to do with the battery when I was going to be working with the car's electric system. I might take it into a shop to have it done, I'm not so sure about working with the serpentine belt.

Luke |

Unknown said...

I have 2002 gmc envoy I'm changing the belt do have to loosen the alternator bolts