my son often chides me for spending to much $$$$$$ on that mechman alt.....but its steady and never has less than 14v.....good investment i think

the 145 amp truck alt should have been standard on F bods !!!!

 

What was the issue if I may ask?

 

A voltage drop (low enough to trigger the "check gauges" light) would occur during heavy throttle only under full drivetrain load (not present with free revving). It was not dependent on rpm or vehicle speed or gear, and I eventually learned that I could duplicate it by simply power braking in my driveway. Electrical load did not matter, but it wouldn't occur until the engine was fully warmed up and engine bay sufficiently heat soaked.

Did a bunch of pertinent diagnostics, couldn't find an obvious cause or anything that tested poorly so I eventually loaded the parts cannon. All checks and/or replacements related to belt/belt tension, various connections for starting/charging/grounds, alternator/battery themselves, etc., were all good and/or ineffective at solving (or even changing) the problem. Of course, the very first check was to verify that the dash gauge was accurately indicating an actual drop in voltage (and it was).

One day while working on this, a friend had come by and was just helping me brainstorm. We took turns power braking it while watching things in the engine bay just to see if anything stood out, and we noticed that an exposed, woven ground strap was routed across the top of the alternator. This is one of the standard factory ground straps, but it was routed a little differently than on my other LS1 F-bodies (I had not moved it during any of my previous tests/checks, including when I swapped the alternator - it was still in the same spot it had always been). When the engine would twist under the torque of power braking, that ground strap would drag across the alternator case directly where the exciter wire connects to the unit. I took a long screwdriver and propped it up and away from that area and the problem immediately disappeared, so I then put some wire loom over it and zip-tied it away from the alternator case. That was in ~2006, and to this day the problem has never returned.

Upon telling this story over the years, several folks have insisted that the ground strap couldn't have possibly interrupted the exciter voltage/signal just by touching the top of the connector. I agree with them in theory, but somehow that is exactly what was happening when the strap would pull across the top of the alternator during engine twist. It was fine just sitting there, or under light throttle, but the twist of heavy throttle must've been moving it in a way that friction or tugging against that connector was disrupting the signal. The problem seemed to originally appear after some spirited cornering one day, maybe something that was already marginal just finally shifted enough to cause a problem, and it always required a certain amount of heat to occur, but once I knew the right conditions to make it happen I could duplicate it at will. Once that strap was moved, I couldn't ever make it happen (nor did it ever happen randomly) again.

 

I'm sure there are thousands of people running the Tahoe FF OS and their alternators charge fine.

I'm also sure there will be someone who will say that it's not possible for that OS to cause the issue and I'm full of ****.

It's amazing how much more you like your car when you figure out a long term problem.

 

When everything "reasonable" has failed to solve the problem, sometimes you have to start thinking outside the box. You may never know exactly why this OS caused a problem in your specific application but seems to work OK in others, but all that matters is that you now have YOUR car straightened out. (and as a side bonus, this information might help someone else in the future.)


That's the most important part.

 

Years ago I worked in a shop and ran the dyno. We put a Whipple on a 6.2 Raptor(we had done several of them)and the customer brought it back saying the truck would shut off going WOT.

I finally figured out how to replicate the problem(you had to drive it a very particular way) and spent the next several months trying to figure out why. I had all sorts of DTC's in every module after it would do it. I scoped every circuit imaginable, had 100's of logs of it doing it, put a different PCM in it, different OS, even took the Whipple back off(ran fine). It was to the point that Whipple told us to ship them the truck.

I took a break from it for about a month, my stress level was through the roof. Unhappy customer, which is completely understandable, unhappy boss, also understandable.

When I started looking at it again, I basically started over and said, it doesn't do it stock, but does with the Whipple and the injectors that came with the kit.

It was the ******* injectors.

At a certain pulsewidth(it had to be that exact pulsewidth), they were drawing so much amperage, it was shutting the PCM off and resetting it. Put another brand of injectors in it and never saw the truck again.

That truck made me quit working on cars. I quit my job and wouldn't work on anything, including my own stuff for over a year.

Until that point in my life, I never understood how a job, could make you hate something that you used to love to do and had been passionate about since childhood.

I eventually started working on things again, but there's no way I would ever go back to doing it for a living.

I apolgize for derailing this thread.

 

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Excellent post.
That a pretty deep dive in the psych, worthy of a 'De-Rail'.
Glad you are back to tuning, and just for FUN .

 

^^ Thanks for sharing that story, it's another example of an unexpected solution (which came at a very high personal cost).

In an effort to not get too far off track, I'll just add this:



This is exactly why I never wanted to do this for a living in the first place; sometimes you just NEED to be able to walk away from a problem and let it percolate in the back of your mind for awhile. You can't really have that luxury when doing it professionally, so burn-out and frustration at work can then lead to hating it as a hobby. I know some guys can manage this, but it's not for me. Sometimes I need to walk away for a bit, just to keep my sanity.

 

Just had my alternator go, at least I think that what it is, car is running fine but all of a sudden voltage was just in the yellow when it usually is 14-15V. I bought the car a few years ago with 87K miles and now it has just over 90K, and I don't know the history plus I had a loose connection at the battery terminal a while back and the battery wasn't charging so I bet that blew the alternator...

Anyway, looking through the threads on how to change it, I came across this thread and while looking for a replacement alternator. Picked up an '03 Silverado alternator from a local junk yard this morning for $35. I got the old alternator out, but can't seem to get the new one in. I confirmed reading here that the Truck alternator is a bit bigger ( I thought it looked bigger).

So, any tips one getting it in? I'm wondering if because I'm lowered and on ramps, the sway bar is more in the way? So my plan right now is to drop the 2 sway bar clamps and I think that will give me the room to get it in there, but I'm open to ideas!

 

If the back of the alternator is hitting one of the power steering lines, clocking the alternator may be in order. That's what I had to do to fit a larger alternator in my TA.

 

I'm not sure what you mean by clocking it, maybe putting some washers behind the bracket to shim it out? But then the idler pulley wouldn't line up with the belt...

B ut at this point, I don't know about that - I can't even get the alternator back above the sway bar. My next step is to drop the sway bar clamps because I think 1/2" of room will do it. I was able to wriggle the old alternator out, but just can't sem to get the bigger truck alternator back in, even twisting the same way

 

Take the fan shroud off. It makes it a lot easier.

I had to "adjust" the p/s lines a little too.

 

Clocking means to remove the back part, turn it as needed, and reinstall in the new position

 

@cbrenthus Clocking when it comes to alternators refers to changing the position/orientation of the alternator. This means the bolts holding the front to back need to be removed and the position twisted clockwise/counterclockwise and re-tightening the bolts. The biggest skill needed is to not remove the cover to the point the bushings come out. Just search for "how to clock an alternator" and you'll find a ton of articles and videos showing how to do this. Selecting the GM versions will help the most with this application.

Start by removing the pulley. Place the alt on the bench with the shaft DOWN.
Remove the 4 bolts. Tap the front case half away from the stater.
Spin the front half to the correct position and re-insert the four screws.
Use caution to not move the housing too much so the brushes don't pop out of position.

 

Thanks all for the info! This is getting wayyy too difficult, think I'm just going to leave the alternator out and install a receiver and tow a generator around LOL! But seriously, I'll check in with what happens - I haven't had a chance to look at it today. The good news is that my wife is very supportive of me getting a lift soon, for stoarage and for these projects. I've wasted quite a bit of time crawling under and back out of the car the last 2 days, plus I have put on garage clothes. If it were up on a lift, I could just go play with it anytime I had a few minutes

 

Have the old alternator tested at a parts store. Anytime that I’ve had an alternator go bad the car would either die shortly while running or it wouldn’t start at all. You said it ran fine but the volt gauge read low. Did you drive it very long? I think about twenty minutes of running is about all I’ve ever gotten before it dies when the alternator wasn’t charging the battery. If you need a new alternator buy a new or reman (not used) that fits. Or did you get a bigger alternator because you’re running a sound system etc? If you can afford a lift there’s no reason to get a junkyard alternator, no offense.

 

Powermaster makes high quality, brand new replacements in the proper CS130 (factory) case size (multiple amperage ratings available depending on your needs). No need to fight with fitting a physically larger unit, especially for a stock application.

The junkyard pricing is nice, but it's a 20 year old unit with an unknown history. It might not last long anyway.

 

All good points! I'm going with the junkyard alternator for now because nobody carries a decent new one anywhere near me. Had I known the process this would turn into, I might have ordered one because it probably would have arrived before I finish anyway, LOL! Next time I'll go new. I I also am not 100% sure what's going on - that last 2 years the car has sat mostly in storage while I moved in and made room in my garage for it. Last year I couldn't get it started, eventually found the terminals were loose on the positive side. Tightened them up and brought it home in December. Stored it until 2 weeks ago, spent the weekend replacing headlight motors, coolant tank, and hatch struts to start driving her again, got her inspected the following Monday, drove as my daily all week then Saturday morning went to take the kids to ice cream and mini golf and noticed the voltage low. Not low enough to trigger check gauges, but just in the yellow. Immediately turned around, drove home and put the kids in my truck (and the car on the tender). Drove it again on Wednesday to get the front on ramps and same thing. Neither time did I see the voltage drop, really, but I didn't run it for more than 5 minutes.

And I'm going with the 145 amp alternator simply because it seems to be recommended. I don't have a sound system, just a pioneer head unit, but why not go 145?

 

Now I'm thinking I might just go with the Powermaster 150 amp from Hawks. $255 after shipping and taxes, I know it will fit, and I'm seeing good reviews. The main reason I went with the KG3 was I wanted to get the project DONE, and it was the quickest (and cheapest way) to get another alternator. However, at this point the project still isn't done, and its going to be several days until I can work on it again and I'd like my garage back. Thinking I might order the powermaster, and back the car off the ramps and put it away with no alternator or belt (I know, no power steering but I've done that before with a broken belt).

 

Summit carries a few different Powermaster CS130 units that will fit your car, different finishes and amperage ratings and such. Shipping would be free so the price should be comparable or better (not sure on your local tax rate). Super fast shipping with them too. Hawks is good also, but I'm not sure if they offer all the different possible versions/finishes.