It required 14 volts to engage starter.
Voltage Drop Test

 

Oh, I see. That is interesting if that's what the "14 volts" meant, is that it required 14 volts to operate.
And I have been binge watching Shrodinger's Cat and ScannerDanners channel this last week trying to learn all I can about electrical systems and troubleshooting.....I even watched that exact video lol. It's a bit late and I'm tired, so can I just ask directly risking looking stupid.....what was your reason for posting that video link? (As we did about every test possible including voltage drop tests in this thread already). Voltage only drops about half a volt (from 12.6 down to around 12.1 volts) at the main stud on starter when cranking. Is there something I'm missing? If the starter "requires" 14 volts on a bench test (without a actually load) to me, that just says something is wrong with the starter.....no?

 

at 14 volts it was drawing 78 amps unloaded, the important thing is the bendix was fully extending so the starter solenoid appears to be working
If as you have posted form your testing that while cranking the battery voltage at the starter drops from 12.6 to 10.2 if I remember correctly allowing for your meter inaccuracy then that's what I would expect your truck to do with the correct battery along with the voltage on the purple wire being 10.5 to 11 volts then the truck should start if all else is good.
With the starter bench tested by Oriellys and it checking good then to me that pretty much leaves us with the pinion gear binding on the flywheel which is preventing the bendix from fully extending therefore not closing the solenoid contacts to engage the starter motor
As you have stated the OEM starter normally doesn't require shimming but there is always that one off situation where things don't always follow the norm.
the easy thing to do to check this theory is to pick up some shims and stick them in there and try it.

 

Ok. How many shims do you think I should try?

 

they come in different thicknesses so start with one thick one and see what happens

I have to commend you, your persistent, I think most would have thrown in the towel and sent it to a shop by now.

Neal

 

78 AMPS at no load seems very high for a free spinning rotor. maybe at initial start because of inrush... but free spinning no load?

 

I appreciate that Neal. I'm stubborn but the other half is I can't stand paying a fortune for "part swapping". Most shops these days just "throw parts at it" never actually doing the proper diagnosis to know for sure what the issue is. It's bad enough paying $120+ an hour labor and then doubling the cost of the parts on you.......but where I literally can't take it......is that you pay for their mistakes. When they guess the "most common cause" like a starter in this case, and that's not what the problem was......I still pay for that part and that labor. (Which is honestly ridiculous). I have had this happen more times than I can count and there is literally not one shop that guarantees their work (meaning if they are wrong, you don't pay). So in summary, "I can throw parts at it just like they can but for WAY less". If there was someone like "ScannerDanner" around me, I would have taken it their long ago.

Frustrating update on the shims. Bought a pack of shims that looked close/like they would work but when got home and opened pack, they don't like up with both holes. Returned and went to GM dealership and every other parts store in town, and no one has ships that fit our starters........any ideas where to get some or what to do? (My only thought is using washers)

 

 

as a test I think washers would work,

If they move the starter to far away it will wine when starting but for now we just want to test it to see if it makes a difference when starting

Neal

 

Well put starter on with a washer on top of starter on each side and that didn't fix it either. (It started the first 3 times, giving me a little hope lol, and then didn't start the next 10 times)

It's always seemed to work better "cold" or act up more "warm". Wether it was early on and it only acted up 1 in 20 starts or wether it's now and it only starts 1 in 20 tries.

But aren't we at the end.....where by tests it can only be the starter itself?

1. Jumper cables run from battery down to starter not working eliminated the main hot and ground to starter....

2. Jumper cables as extra ground from starter housing to block, starter housing to frame, starter housing to negative battery terminal......not working....further eliminates any grounding issue....

3. Jumper cables from our other truck (2007 Yukon) to the Hummers battery.....not making a difference eliminates the Hummers battery. (And it tested good under load test at O'Reilly's).....

4. Using a small 18 gauge jumper wire from the "S Stud" to the "Main hot stud" on the starter not starting it....... eliminates ALL ignition side..... correct? (Eliminates ignition switch, neutral safety switch, AND things like the PCM, body modules, relays, ect correct?)