Effects of weak battery on performance

[george]

I noticed a week ago or so my car would not start after sitting 24 hours. Threw on a charger and it started right up. Car had been sitting all winter on a trickle charger. Never has been a fast starter either. Well it did it agan last Monday so I pulled the it out to test it. Votage was over 12+ volts. I found one cell was dead, the rest showed 75% charged so replaced it with OEM battery. Car now starts up faster then ever.

I read where our computers are effected by weak battery voltage and it could cause performance issues especailly at higher RPM ranges like racing. Any responses appreciated.:mug:

[sodian]

I believe a week battery was the cause of my recent column lock issues. I took it in for the K harness and lock plate removal. Two days later the message pops up again. I was told that anything under 12.5V can cause problems. I replaced the battery which was about 12.1V at the terminals even though the car started just fine. The new battery was just over 13V. I have not had the problem for over a week now. Don't depend on the DIC for a voltage reading. Mine is off by 1/2 V compared to the readings directly on the battery terminals.

[racingvette]

Proper voltage is very important, no different then if the house A/C was low and how a TV or other electronics would function under lower voltages.

One example is the fuel injectors.
They get voltage directly from battery.
The PCM to assure some limp mode function and to makeup for voltage differences monitors the voltage and adjust the injectors ON time to try and keep the fuel flow constant.

As voltage gets lower the injectors would flow less so the PCM increases or reduces injectors ON times as voltage level changes.
This effects performance and the PCM itself ( as all other controllers in the car) really will not function well under 12 volts

Keep in mind voltage drops, it could be 12.1 volts at the battery but voltage drop by the time it gets to PCM which could be getting 11.7 volts.

The more electronics added to cars yet still using 40 year old 12 volt designs forced GM to up to 14.5 volts but the wiring is too small a gage to handle the current loads of parts like relays, fuel pumps, HUD, Onstar, etc.

SAE wanted to go to 48 volt system standard but Japan has been holding this up for 6 years as they wanted their patents of 42 volts designs to then charge all vendors for that design.

[george]

Originally Posted by racingvette

Proper voltage is very important, no different then if the house A/C was low and how a TV or other electronics would function under lower voltages.

One example is the fuel injectors.
They get voltage directly from battery.
The PCM to assure some limp mode function and to makeup for voltage differences monitors the voltage and adjust the injectors ON time to try and keep the fuel flow constant.

As voltage gets lower the injectors would flow less so the PCM increases or reduces injectors ON times as voltage level changes.
This effects performance and the PCM itself ( as all other controllers in the car) really will not function well under 12 volts

Keep in mind voltage drops, it could be 12.1 volts at the battery but voltage drop by the time it gets to PCM which could be getting 11.7 volts.

The more electronics added to cars yet still using 40 year old 12 volt designs forced GM to up to 14.5 volts but the wiring is too small a gage to handle the current loads of parts like relays, fuel pumps, HUD, Onstar, etc.

SAE wanted to go to 48 volt system standard but Japan has been holding this up for 6 years as they wanted their patents of 42 volts designs to then charge all vendors for that design.

Thanks, it makes sense to the reasoning that my car started to surge/lean out my last couple runs at 65-7000 RPM. Appreciate the info.:mug:

[zeta08]

But wouldn't the volt regulator keep the charge at the peak value for full charging if your altenator is working? A bad battery would read less than 12.6 when sitting, but I wouldn't blame the battery (unless it's really really weak) for a charge less than say 13.5 when the car is running, I'd look elsewhere. What does your DIC say when you are at say 2000 rpm? Mine is always around 14-14.5...because the alternator is trying to charge the battery. The power of the battery may be weak (CA) but the voltage should be transiently as high as the DIC says or close. I wouldn't think this would effect the FI as the current they pull can't be much. No expert, just my thoughts...

[george]

Originally Posted by zeta08

But wouldn't the volt regulator keep the charge at the peak value for full charging if your altenator is working? A bad battery would read less than 12.6 when sitting, but I wouldn't blame the battery (unless it's really really weak) for a charge less than say 13.5 when the car is running, I'd look elsewhere. What does your DIC say when you are at say 2000 rpm? Mine is always around 14-14.5...because the alternator is trying to charge the battery. The power of the battery may be weak (CA) but the voltage should be transiently as high as the DIC says or close. I wouldn't think this would effect the FI as the current they pull can't be much. No expert, just my thoughts...

Car ran strong Saturday night pulling 7000 RPM every run. Just the usual 2.00+ sixty foot times. Last run an 11.54 at 126.47 mph so I can't complain. Also notice putting car in reverse stopped some type of draw down on my battery. Had the trickle charger on the new battery and light stayed red then put the car in reverse in 5 minutes light was green. My car is a 12/05 build 2006 Z06. Maybe just coincidence but something has been drawing down my batteries. :mug:

[racingvette]

Originally Posted by zeta08

But wouldn't the volt regulator keep the charge at the peak value for full charging if your altenator is working? A bad battery would read less than 12.6 when sitting, but I wouldn't blame the battery (unless it's really really weak) for a charge less than say 13.5 when the car is running, I'd look elsewhere. What does your DIC say when you are at say 2000 rpm? Mine is always around 14-14.5...because the alternator is trying to charge the battery. The power of the battery may be weak (CA) but the voltage should be transiently as high as the DIC says or close. I wouldn't think this would effect the FI as the current they pull can't be much. No expert, just my thoughts...

The alt does not put out maximum voltages all the time as the PCM commands the Alt as what it should output to help reduce Alt drag on engine load that would consume more fuel

It is not just the voltage level but the battery ability to hand the current loads. One weak cell would not prevent voltage to be low but would cause problems with higher amperage devices like solenoids or relays.
The PCM cannot see/monitor current load so the voltage could look normal so PCM commands Alt to output less but really the battery cannot maintain the current drain.

To help save weight GM uses undersized wiring gage which does not help when current loads are high and because of low as 5 volts used for some functions and voltage drops does not help when battery is weak and no amount of higher voltages will correct that.

Alt is charging the battery but the voltage/current loads still come from the health of the battery.

Also the controllers are designed to function above 12 volts as a way to try and overcome that there is way too much electronics in cars today using 40 year old 12 volt systems so like the PCM reacts and even goes into a limp state when voltages get around 12 volts.

Look at late model year C5s, to try and help GM used a higher output Alt then in earlier C5s.
When you use the newer Alt in older C5s the PCM trips over voltage error codes requires a different PCM flash that has higher voltage triggers programmed in.