85 Vette Overcharging Battery
Thread Starter
Advanced
Joined: Apr 2015
Posts: 52
Likes: 6
85 Vette Overcharging Battery
I have a 1985 Vette with only 318 miles that has been stored for 30 years. I've just been thru the process of getting it running after sitting all those years. Put MMO in the cylinders, let sit overnight and then hand rotated the engine 6 full revs. Then put new battery in & cranked engine with the plugs still out to build oil pressure to the upper valve train & blow out the MMO. Drained the old gas in tank & put in 2 gallons fresh premium. I didn't do anything else to the fuel system, gas tank, fuel pump, or lines. When hooked everything back up and tried to start I now have a multitude of problems. The big issue I need to fix 1st though before I can address anything else is this. Was very hard to get to start & run. When it finally did it runs very rough and will only keep running if I hold at high RPM around 3000. When I did this the volt gage showed a red light and 18.1 volts! It overcharged the battery so bad it blew a lot of battery acid out the vent tubes. Can anyone help with what may be causing this very bad overcharging?
Melting Slicks
Joined: Jan 2001
Posts: 2,940
Likes: 5
From: Chesapeake VA
Overcharging is caused by a bad voltage regulator in the alternator. You will need a new alternator or a rebuild of the one you have.
Having to hold a high rpm to keep the engine running is often a sign of a significant vacuum leak. A smoke test will show if that is the cause.
Having to hold a high rpm to keep the engine running is often a sign of a significant vacuum leak. A smoke test will show if that is the cause.
Last edited by Square; Jun 30, 2017 at 10:23 PM.
Zen Vet Master Level VII
Joined: Mar 2016
Posts: 5,218
Likes: 1,174
From: Southlake, TX
Your voltage regulator is.. not...regulating.
Congrats on a low mileage beast, but as you are discovering that "waking her up" is no an easy task. My guess is that you will have a lot of cleaning and un sticking to do.
Congrats on a low mileage beast, but as you are discovering that "waking her up" is no an easy task. My guess is that you will have a lot of cleaning and un sticking to do.
Thread Starter
Advanced
Joined: Apr 2015
Posts: 52
Likes: 6
OK, but remember this is basically a brand new 30 year old Vette, (only 318 miles). Would the voltage regulator in the as new alternator go bad from just sitting in the garage all those years without being run? Also what method do you use to do the smoke test?
Drifting
Joined: Mar 2013
Posts: 1,952
Likes: 239
From: Venice Cali.
giving. Clean connectors on alt , battery. Good luck!
Thread Starter
Advanced
Joined: Apr 2015
Posts: 52
Likes: 6
Thanks billschroeder5842. I was replying to Square when your response came thru. I figured it probably was the voltage regulator but couldn't figure why it would go bad from just sitting & that's why I'm stumped. One of the other problems I'm having is besides it running very ragged & missing, is the left cylinder bank seems to be getting much hotter than the right side after just a couple minutes of running. This would kind of indicate most of the misfiring is on the right side. What would cause this?
Drifting
Joined: Mar 2013
Posts: 1,952
Likes: 239
From: Venice Cali.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Zen Vet Master Level VII
Joined: Mar 2016
Posts: 5,218
Likes: 1,174
From: Southlake, TX
My suggestion is that you give your car a chance to "wake up" slowly. Although "newish" after 30 years, it is certainly not a new car. There is more rust, corrosion and deterioration than you can imagine.
You high idle is probably the result of a vacuum leak. Any thing rubber is suspect and prone to cracking. Being pressurized (and expanding) for the first time in 30 years, you will no doubt have air and fluid leaks.
Your running rough is probably your injectors being dirty (gasoline that has turned into a varnish type substance) that will either work themselves out or need to be replaced. Your fuel rails are most likely gummed up.
Your engine sensors connections probably need freshening. Start with your coolant sensor, then IAC and the O2.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
Burning Brakes
Joined: Oct 2001
Posts: 911
Likes: 5
From: TN
voltage reg
Overcharging is caused by a bad voltage regulator in the alternator. You will need a new alternator or a rebuild of the one you have.
Having to hold a high rpm to keep the engine running is often a sign of a significant vacuum leak. A smoke test will show if that is the cause.
Having to hold a high rpm to keep the engine running is often a sign of a significant vacuum leak. A smoke test will show if that is the cause.
Thread Starter
Advanced
Joined: Apr 2015
Posts: 52
Likes: 6
So I can replace just the voltage regulator and not have to buy a whole new alternator? Some say the regulator can be replaced and others say it cannot unless the alternator is taken to a rebuilder. Is this something I can do? Are there instructions online anywhere?
Thread Starter
Advanced
Joined: Apr 2015
Posts: 52
Likes: 6
Thanks to "ihatebarkingdogs" for both your responses. 1st, I didn't think the ECM would shut down the engine in an over voltage condition. I had read where this would damage the ECM if operated for a prolonged period. Hopefully mine is not harmed as it only ran a few minutes before I noticed the red over-voltage indicator & 18+ volts on the gauge.
2nd, thanks for the info on changing the regulator and also the things to test before changing it out. I shouldn't have a voltage drop on this car, but I'll check it.
2nd, thanks for the info on changing the regulator and also the things to test before changing it out. I shouldn't have a voltage drop on this car, but I'll check it.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
That's the way that I remember it, but it's been a couple of years since I looked at the code. Something to do with overheating the injectors if the voltage is too high.
I looked briefly at the code just now and only found the error code 53 if the voltage is over 17.1 volts.
I looked briefly at the code just now and only found the error code 53 if the voltage is over 17.1 volts.
Team Owner
Joined: Jul 2004
Posts: 28,474
Likes: 3,291
From: Hartford WI
Why would you want to do that? You can replace the regulator but it is kinda old so I would take it to a rebuilder and have them go through it. Make sure other things are in spec and not on the way out. You can change the regulator yourself if you have a couple tools but you can't test it. Before you ask, I had Autozone or a store like that test my starter. They said it was OK. Rebuilder found oil leaked into it and crudded up things. I had to teach them how to do the ignition module test. Sorry, not much faith in these stores.
Melting Slicks
Joined: Nov 2013
Posts: 3,451
Likes: 336
From: Greater Cincinnati Area.
Given all the computerized gizmotry in the C4 and if it is actually boiling electrolyte out of the battery? I wouldn't play games with this AT ALL. Just change it, imo.
I bought a really, really nice van once and it ran FINE. Everything was perfect but the trans was out, so I got a steal on it. It sat for a couple months till my parents said they wanted it, so I went to put a trans in it and the engine is locked up! I can't believe it. I parked it there myself!! It was fine!!! FTW?
Well, the alternator managed to corrode a little bit and stuck the armature. I tried to break it loose and it actually cracked the case. It stuck that bad.
There's no telling what is going on inside a 30 year old alternator. I'd just replace it and potentially save yourself a host of problems.
But, that's JIMO.
Good Luck!!
I bought a really, really nice van once and it ran FINE. Everything was perfect but the trans was out, so I got a steal on it. It sat for a couple months till my parents said they wanted it, so I went to put a trans in it and the engine is locked up! I can't believe it. I parked it there myself!! It was fine!!! FTW?
Well, the alternator managed to corrode a little bit and stuck the armature. I tried to break it loose and it actually cracked the case. It stuck that bad.
There's no telling what is going on inside a 30 year old alternator. I'd just replace it and potentially save yourself a host of problems.
But, that's JIMO.
Good Luck!!
Last edited by confab; Jul 2, 2017 at 06:06 PM.
Zen Vet Master Level VII
Joined: Mar 2016
Posts: 5,218
Likes: 1,174
From: Southlake, TX
It's a 314 mile car. Perhaps retaining the born-with, "matching number" alternator is a consideration? ......
Put a regulator in it, and put it back on the car. Original cars are only original once. Every time something gets changed, it is just a little bit less original.
Put a regulator in it, and put it back on the car. Original cars are only original once. Every time something gets changed, it is just a little bit less original.
Melting Slicks
Joined: Nov 2013
Posts: 3,451
Likes: 336
From: Greater Cincinnati Area.
If it is important to you, OP, I just googled about a billion GM alternator rebuild videos on youtube. (Only a slight exaggeration, I assure you.)
It's pretty old, so you can at least give it a good once over when you're in there and hopefully spot any other lurking crap.
Good Luck!
