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Discussion Starter #1 (Edited)
Hello all. I've had the same hot start issue as everyone else and replaced the starter - the battery should be in good shape as well. It was starting fine when hot for a couple of weeks then went back to slow starts and the windows lose their index often (i.e. the window does not roll up when I shut the door). I re-index the windows per the manual every time they lose their place which is maybe once or twice a week.

This leads me to believe there is a short somewhere or perhaps the alternator isn't doing a good job. I mostly go on short trips so this may also be the reason for slow starts but the battery voltage is fine at ~13.5-14V.

Before going through more effort than I need to, has anyone had a similar issue with the windows combined with slow starts? Any ideas?

Thanks

EDIT:
 

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Z06 Tech Advisor
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1,820 Posts
It would help if you mention what year and model

A battery may have the voltage but cannot handle current loads so first thing is load test the battery
to see if there is not a bad/weak cell.

If your NOT using a battery tender and car sits then battery over time will lose 1 or more cells get weak

If on a start there is a high amount of current load and drop of voltage but not only effects starter load
but also yanks the cold start voltage low enough where the car's controllers cannot function correctly and
this could cause a controller's stored memory for settings to be erased.

Also to be sure is monitor the voltage during a start and see how low the voltage goes and do not forget
about voltage drops due to distances of wiring as controllers cannot operate less then like 12.5 volts.

If there was a short then a fuse would have blown, you could put a current meter in series of battery lead and battery lead and determine if there is a relay or controller not going to sleep and if so then pull a fuse at a time to find which circuit is staying awake
System is designed that once ign key is turned off trips a time counter, after 15 minutes controllers should go to a sleep mode and reduce voltage/current loads.

Check grounds being clean and tight.

Under the floor hatch on passenger side is another fuse panel, the BCM and the starbus network
Assure all is dry, clean and all wiring connections are firmly plugged in

If a C6, there was a issue with the ALT wiring connectors, best case if using a OBD-II scanner ( not a code reader)
is look at the ALT parameters and see if the PCM is commanding the ALT to output or not.
 

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Discussion Starter #3
It would help if you mention what year and model

A battery may have the voltage but cannot handle current loads so first thing is load test the battery
to see if there is not a bad/weak cell.

If your NOT using a battery tender and car sits then battery over time will lose 1 or more cells get weak

If on a start there is a high amount of current load and drop of voltage but not only effects starter load
but also yanks the cold start voltage low enough where the car's controllers cannot function correctly and
this could cause a controller's stored memory for settings to be erased.

Also to be sure is monitor the voltage during a start and see how low the voltage goes and do not forget
about voltage drops due to distances of wiring as controllers cannot operate less then like 12.5 volts.

If there was a short then a fuse would have blown, you could put a current meter in series of battery lead and battery lead and determine if there is a relay or controller not going to sleep and if so then pull a fuse at a time to find which circuit is staying awake
System is designed that once ign key is turned off trips a time counter, after 15 minutes controllers should go to a sleep mode and reduce voltage/current loads.

Check grounds being clean and tight.

Under the floor hatch on passenger side is another fuse panel, the BCM and the starbus network
Assure all is dry, clean and all wiring connections are firmly plugged in

If a C6, there was a issue with the ALT wiring connectors, best case if using a OBD-II scanner ( not a code reader)
is look at the ALT parameters and see if the PCM is commanding the ALT to output or not.
Thanks for the input. It's an 08 Z06 by the way. The reason I can't seem to think it is the battery is because the car will sit over a week and then crank up no problem. Then with a bit of heat it will start slow after an hour of being turned off. I do agree with the fact that the voltage must be dropping low enough to impact some of the other electronics. Maybe the resistance/impedance is impacted significantly once everything is hot and my new starter (OEM) is requesting enough current to make a difference. I'll perform a load test on the battery. This all started after I replaced the starter. My clock also disappeared from my nav display as well which is weird.
 

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Z06 Tech Advisor
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Being you replaced the starter for a problem and then still had problems leads to real issue and I agree
heat changes resistance including to a cell in battery
With engine heat soaked, if a battery charger hooked up, does problem not occur ?

Being problem with clock, I would think would be with the radio controller
Index of windows a issue, BCM controller,
Start issue is tied to both the BCM and PCM so now that is multi controllers

IF load test done after engine bay heat soaks passes then battery can be taken out of the possibles
Next would be grounds, as most controllers command functions by reference to ground so if weak, loose, dirty, etc
ground highly effect controllers.

Check again by BCM under floor hatch, closely look at the Starbus, BCM, etc wiring connectors, see if some mouse has not gotten in there and also where PCM is located that has been chewing on wire looms.
Check main engine to chassis ground, rear of left backside of head to chassis.

There is multi spice packs grounds, look on frame, see multi grounds going to a little box that bolts to chassis
That splice pack comes apart, a bit of bitch doing so but inside are male and female connectors, clean up well

When cold, open door, does the security light on dash flash ?
When hot does it still flash ?

Starting issues sometimes is there is a safety switch on clutch pedal, if out of adjustment or faulty switch causes a crank but no start.

Focus on the BCM connectors, see if any water stains showing
Take inner fender side off on right side to get to PCM, check grounds and wiring and pins of wire looms

You really need a OBD-II scanner, to see if ANY controller is hiding any error codes or U codes which means a controller(s) cannot talk on the Starbus network
 

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Discussion Starter #5
I had the battery tested after driving for about 5 min - maybe the car wasn't hot enough but the battery came back as good. When I started the car with the tester connected it gave a "starter fail" message even though the car started relatively normal.
 
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