nuke61

As an FYI, I have this posted in the C6 Tech section also.

This is one I've never seen, and I did a search, but I couldn't find an issue like this one.

1. I'm out driving the car around, and I get a charging system fault message.
2. I watch the voltage on the DIC slowly drop from ~12 volts (normally sits at 13 to 14 volts) all the way to 10.5 volts
3. No odd behavior otherwise - stereo is still working, A/C running
4. I drop down a gear, thinking maybe it just needs more rpm - no change
5. I'm driving for ~10 minutes this way, hoping I can make it home to investigate.
6. Just before turning into my subdivision, I give it a quick rev to ~6000 rpm
7. Voltage rapidly climbs to ~13 volts, then slowly up to its normal ~14 volts
8. I shut it down, immediately start it back up (no issues, like normal) and voltage is rock solid at ~14 vdc

WTF ?!?!

Patriot Six

Mordeth

It's likely the alternator or the connections at the alternator. Make sure the bolt holding the wire in place didn't loosen and that the wires appear in tact and not broken/frayed. If that all looks good then the alternator itself probably **** the bed. I've replaced mine more times than I can count and actually carry a spare one with me to the track. Simple procedure that takes about 15 minutes.

GOLD72

I just had my 2011 ZR1 alternator replaced at 46k miles. New battery was installed last December and then again with the alternator replacement yesterday. No problems with engine startups. Was within 3 miles of home from the office one hot afternoon last week when the AC suddenly started blowing hot air. Then various system fault alerts started showing up on the DIC or dash such as Shocks Inoperative, Air Bag System not ready, Low Voltage, etc. I brought up the Voltage on the DIC and it was running less than 9.0 volts so I knew I was in trouble and running on battery electrical only. I turned off all of the unnecessary electrical loads. I got home with the DIC at 8.2 volts. The battery charged back up overnight with my 10 amp charger and started the car just fine but the system voltage was only about 11.7 volts while driving with no AC or radio so I was pretty sure the charging system output was well below spec. First electrical failure of an alternator in my 50 years of car ownerships. All covered with my GMPP and battery warranties.

nuke61

Thanks for the all the input Early this morning it did the same thing - started right up, volts at 14 or so, stopped at a gas station, when I restarted it was at 12 vdc and dropping, so I went back home and got the other car to drive to work. Oh, I checked the alternator cable for tightness, good to go. I disconnected/reconnected the L/F/A 4-pin connector a few times to wipe the contacts, so I'm going with bad alternator @80k miles, its entire life in the Phoenix metro area.

I called Mechman today to ask if they had any alternators for an LS7 lying around (that's what their website suggested in a rush) but was redirected by Josh at Mechman to Bret Bradbury, aka Blownbluez06, because Brett specializes in late model Corvettes, and keeps the basic Mechman alternators in stock. Nothing special, machined finish, 170 amps - it should be on its way later today.

Patriot Six

Brett is great to work with and is who I got my Mechman from. I also got his bypass cable.

Dale1990

It might also be helpful to check/clean the ground connection on the engine block near the starter and to check the cables on the starter for corrosion or head damage. I agree with the others that it's probably a dead alternator (I'm on my 2nd parts store version) but these connections can also cause charging issues.

nuke61

Yeah, I bought the bypass cable too. The price was too close to what it would cost me to do it myself, that that would be without a hydraulic press connector.

Dale1999, the bypass cable apparently goes from the alternator output directly to the power block on the passenger side. Much better current capacity than stock.

SweetZO6

Edmlaser

Had this exact same thing happen to me. And, It happened to a friend of mine.
It was the STARTER in both of our cars! The connection from the alternator to the battery is connected on the starter. That connection was chard and melted causing all kinds of voltage issues that would come and go.

Unreal

Bret is amazing. Was going to offer to let you borrow my mm to see if you like it.

nuke61

Thanks, I'll take a look at that too.

nuke61

Thanks for the potential offer :-)

For the extra $100 or so over an OEM type replacement, it seemed like a no-brainer to go MM, with their tighter tolerance parts, 6 phase instead of 3 phase wiring, for efficiency - and Brett said that while its not perfect, and still breaks, the MM stuff is much better than anybody else's stuff. I also appreciated that he does high current D.C. work for his daytime job, and looked at the Corvette in terms of failure points. In the 20 minutes that I talked with him, it was clear to me that he has a deep knowledge of the Corvette electrical system, it's weaknesses and fixes.

spy2520

Had the exact same issue just recently. Same symptoms. Replaced starter and also bought a cable to run directly from alt to the terminal on the fuse block.

GOLD72

Well after 1-1/2 commuting trips to the office this week with no further issues, the engine refused to start yesterday afternoon in the office parking garage. One click of the starter solenoid bendix and that was all I could ever get with each start try. Office buddy couldn't jump start it either with his truck. Then AAA showed with no success either. By that time, I had the previous dealership send a flatbed to come get the car from across town during rush hour. Obviously what is wrong with it wasn't the alternator and/or battery. Now thinking a bad connection that the dealership didn't look for last week like the starter positive cable connection. There were closer dealerships but I didn't want to get them involved since my local neighborhood dealer dealt with this issue just last week and they should stay on it. Took 3-1/2 hours before I was on the way to the dealership in the flatbed. Plus I had to get help to push the car out of the office garage from the 2nd floor since the flatbed driver warned me the hour before arrival that he couldn't get it inside the garage due overhead clearance.

Apocolipse

Could always just bump-start it....or is this no longer an acceptable thing in society lol

GOLD72

On a serious note, can these cars be started by getting it rolling downhill with the ignition on and then momentarily dumping the clutch to get the rear wheels to spin the engine?? I did that with several cars decades ago when they still had carburetors and distributors. I am thinking not since the fuel and spark is all ECM controlled now and fuel and spark may not be applied unless the normal starting sequence is being accomplished. Also seems like some have said no on this forum as well over the years.

Patriot Six

Apocolipse

Yes you can! I was being serious

nuke61

Well, I think the starter was the issue all along, because I went out for a drive after starting the car without any issues, and it would not start at the store parking lot. Just a single 'CLICK' and that was it. Battery voltage was good at ~13 volts, but just one solid 'CLICK' and nothing. Had it towed home, and when I rolled it off the flatbed, I stuck it in reverse and bump started it so I could drive it into my garage and onto the ramps. I'll be taking a look at it this weekend.