battery voltage Low?

[bobnsue2]

Hi,

My 91 STS 4.9 has this bad surging when first started and along with swapping out most things, except the injectors (which test good) I noticed the voltage is a bit low.

Once it warms up it runs great.

The voltage is around 13.4, 13.2, as low as 12.8. Occasionally it gets up to 13.9.

I had both the battery and alternator up to the NAPA store and both tested fine. The alternator is putting out 137 amps (140 amp alternator) and 14.7 volts on the test bench..

What the heck is going on?

I wonder if the lowish voltage could be the reason it runs so poorly?

I see 12 volt systems run at 14.7 while running even if the battery won't hold up overnight.

I wonder if the computer could be causing this.

BTW, lights, A/C and radio are off.

Thanks for any thoughts,

Bob B

[paran0id]

Im no expert, but I believe that as long as your voltage is above 12V you are fine. In older cars, the battery was only used for starting and once the engine was running, the alternator was used to power all of your accesories. I dont know if newer cars are the same but I imagine they are. As long as your alternator is putting out above 12V ( I would check it under load, AC, radio, defrosters etc on) it should charge the battery fine. If the voltage is constantly jumping around, and both the alternator & battery have tested good, I would check all of the electrical connections at the battery, (clean them real good with baking soda & water, then dry & cover in dielectric grease) and also check any other grounds. Bad connections & grounds are notorious for intermittent electrical problems..

[adallak]

bobnsue2,

You may have bad ground on the engine block.by the starter. Remove and clean the stud by the starter. Install new star washers on both sides of the stud to engine block.

You can run diagnostic to check the condition of that ground. The snapshot data ED10 should show battery voltage 13.0 or above. I checked out mine today and it was 0 ! I have hard time starting the car when it is is really hot, have to wait till it is down to 170 F. I think tha ground is the culprit and gonna fix it some time soon.

[johnnydone]

13.2-13.7 is great for a fully charged battery you will see 14.2+ if the battery is not fully charged or wont hold a full chg just life experiences

[maydog]

If the car isn't yelling at you there probably isn't a problem. I think the voltage is regulated according to a temperature sensor somewhere under the hood. This helps keep the battery from overheating and increases its longevity?

Maybe someone with a shop manual can verify this.

[Scotty]

I don't get the impression that your charging levels are bad, they seem right on.. I used to get 13.8 to 14.1 after startup and then it dropped down to 13.3 or so. They only get above 14 in the winter time. If my idle was low, or if I had a lot of accessories on I would drop below 13 but it was rare but as long as its above 12 its ok.

By the way, that was a good guess because when my battery went bad, my alternator would NOT run the engine, but it was the battery not the alternator, the engine WILL NOT run on the alternator as was previously mentioned..it needs a good battery to run, the coils draw quite a bit of current.

Do me a favor and check to see if your EGR valve is hanging OPEN at all, that will destroy your idle. Have you pulled it yet to clean it? If not buy an EGR gasket and remove it and clean it with a wire brush, tap the frame that attaches to the engine with a hammer to loosen dirt, and try to use a small brush to clean the pindle seat.. Don't get solvent on the diaphram. Don't breath the dust.. Mike

If it is stuck open the slightest bit it will cause a bad idle, wear gloves and try pushing up on the diaphram while the car is idling it should stumble.

How did you determine that injectors were good? Do you have any rotten egg smell?

[JohnnyG]

You may also have high resistance in your battery cables. Where are you checking the voltages? If the battery is in the back seat, like my '99, the long cables to the engine can corrode inside, causing a voltage drop where you need it the most, at the engine. I really don't know much about the '91, but felt it was worth mentioning.

[JimD]

Hi,

My 91 STS 4.9 has this bad surging when first started and along with swapping out most things, except the injectors (which test good) I noticed the voltage is a bit low.

Once it warms up it runs great.

The voltage is around 13.4, 13.2, as low as 12.8. Occasionally it gets up to 13.9.

I had both the battery and alternator up to the NAPA store and both tested fine. The alternator is putting out 137 amps (140 amp alternator) and 14.7 volts on the test bench..

What the heck is going on?

I wonder if the lowish voltage could be the reason it runs so poorly?

I see 12 volt systems run at 14.7 while running even if the battery won't hold up overnight.

I wonder if the computer could be causing this.

BTW, lights, A/C and radio are off.

Thanks for any thoughts,

Bob B

Electrical (magnetic) devices such as fuel injectors are rarely voltage sensitive. I would bet your injectors would "open" normally with voltages as low as 9 volts, or less. Easy to check your injectors by jumpering in a 9 volt dry cell battery.

[QbanCgar]

i had the same problem, got n my car & got the Battery No Charge on my message screen. about 2 days later my car gave out & currently n the shop. u may want 2 have your serpentine belt checked as well. when i got my last oil change b4 i had it done last week, the mechanic had told me that my serpentine belt was cracked & i should get it replaced.

[adallak]

bobnsue2,

Another quick test- pull out vacuum hose from EGR valve and see if your idle improves.

If something wrong with your EGR SOLENOID (say, no voltage on it at all) it will be open all the time supplying the EGR valve with vacuum at idle. Try it wont hurt anything, you may get some spark knoch when the engine is hot , it is not terrible, you can put the hose back any time. Just pull it really carefully they brake easily.