Strange No-Start

[I_bRAD]

Battery voltage at rest: 12.7 V
Battery charging voltage 14.6 V
Temperature: Cold (~-25C)

When I go to start it in the morning the door locks and interior lights work, but nothing when I turn the key. I had it on charge overnight and it still gave nothing this morning. Not even a click.

Starter contacts were changed one year ago. Starts right up with a boost. Starts right up again as long as it hasn't sat for a while. Haven't tested voltage under load, but I would think it would at least make an effort even if it were weak.

Seems like a bad battery, but is it possible that a bad battery can still hold 12.7V at rest and appear to take a charge? Don't want to replace a battery for no good reason but am stumped at what else it might be.

Any ideas appreciated! Thanks.

 

[thecole1098]

The battery could have a bad cell.

 

[theesotericone]

The battery could have a bad cell.

It could but a dead cell will usually read in the high 10's not under load. I'm gonna go with the old check your grounds line on this one.

Charging voltage doesn't tell you much in this case other then the alternator is working properly. If that voltage doesn't settle to the 13.5 range after running for a bit then a bad cell would be more likely. The alt will put out max capacity to try and charge a dead cell battery. Then you fry the alt cause it's working 100% all the time.

OP. Check voltage while under load car off. Then check voltage car running after 15 minutes. Check your grounds while your doing this.

 

[I_bRAD]

It could but a dead cell will usually read in the high 10's not under load. I'm gonna go with the old check your grounds line on this one.

Charging voltage doesn't tell you much in this case other then the alternator is working properly. If that voltage doesn't settle to the 13.5 range after running for a bit then a bad cell would be more likely. The alt will put out max capacity to try and charge a dead cell battery. Then you fry the alt cause it's working 100% all the time.

OP. Check voltage while under load car off. Then check voltage car running after 15 minutes. Check your grounds while your doing this.

12.71 at rest. 10.75 cranking for a good 10s

Will check grounds and go for a spin then check charging voltage again.

 

[theesotericone]

12.71 at rest. 10.75 cranking for a good 10s

Will check grounds and go for a spin then check charging voltage again.

If your getting 10.75 under crank your battery should be fine. That's a really good number actually.

Check your grounds and see if you can find any loose or broken. Clean both battery posts and terminals till they look like new. If your still having the issue you'll have to test the starter wires. Both the constant 12v hot larger wire and the smaller trigger wire. The larger wire should have 12V at all times. The trigger wire should have at least 11V while cranking. Good luck that harness plug is a ***** to get at on a 4wd rig. lol

 

[CB3G_GM]

How old is the battery? Any slow cranking symptoms recently? Voltage is not a full proof indicator of a battery's ability to crank the starter. An old battery can read normal voltage and not have enough amperage (cold weather and weak grounds also help this along)

 

[I_bRAD]

If your getting 10.75 under crank your battery should be fine. That's a really good number actually.

Check your grounds and see if you can find any loose or broken. Clean both battery posts and terminals till they look like new. If your still having the issue you'll have to test the starter wires. Both the constant 12v hot larger wire and the smaller trigger wire. The larger wire should have 12V at all times. The trigger wire should have at least 11V while cranking. Good luck that harness plug is a ***** to get at on a 4wd rig. lol

0 ohms resistance battery negative to alternator case.

The "eye" on the battery is still green too, so I at least know it's full.

Still charging ~14.6 after a drive, but as soon as I shut the car off it drops to 12 (just radio and DRL) so that makes me more suspicious of the battery

Battery terminals are in good shape but will clean them anyhow and try again tomorrow morning. I've got another project in the garage at the moment that isn't moving until the subframe goes on so I'd probably just continue to boost it rather than try to get at the starter wires in my driveway, in the cold and dark!

Bad ground would still be an issue with a boost though, right? I'm having a hard time wrapping my head around that one. What am I missing?

 

[I_bRAD]

If your getting 10.75 under crank your battery should be fine. That's a really good number actually.

Wait. Injectors don't use much juice do they? the cranking value of 10.75 was with the EFI relay removed. I didn't think that would make a difference but I guess technically it could.

 

[thecole1098]

That EFI relay being out will kill the fuel pump as well. But that test was to see how the battery did under a large load (starter turning over). The pump and injectors obviously put a load on the system but not as larger as the starter.

 

[I_bRAD]

That EFI relay being out will kill the fuel pump as well. But that test was to see how the battery did under a large load (starter turning over). The pump and injectors obviously put a load on the system but not as larger as the starter.

I didn't consider the fuel pump, but yeah, I guess the starter is a pretty big draw. I just pulled the relay cause it was the first thing that came to mind to get it to crank without starting, but then reconsidered my technique after!

Terminals are shiny bare metal. battery is currently showing full charge. connections are tight. block heater is plugged in. We'll see what happens tomorrow morning!

 

[theesotericone]

Bad ground would still be an issue with a boost though, right? I'm having a hard time wrapping my head around that one. What am I missing?

When boosting your pushing more amps then just the battery alone so a weak ground can still get enough amps to function. That's why you always check all grounds first in this case.

 

[I_bRAD]

Update:

Cleaned the battery terminals and the next morning it was a bit hesitant to start cranking, but did, and then started up no problem. Much warmer this morning (~-10C) and it started without issue.

Battery is currently charging at 14.5-14.6 V though, getting lower as I arrive at work (1 hour commute) It was a new alternator in the summer, and when I installed it, it was charging at 14.2. It was obviously much warmer then though.

Perhaps I was expecting too much out of it when it was so cold. Going to leave as is for now and see what happens during the next cold snap.

I've got a long list of stuff to do on the truck once the garage is clear, so I'll take a good look at the grounds and starter connections at that point if I don't have to take action sooner.

Thanks for all the help guys.

 

[thegipper]

I would go through all of the grounds and make sure they are clean and making good contact. They can often rust or corrode under the terminal and give you intermittent trouble. There should be grounding wires to the body, transmission and engine.

Also, slightly peel back the insulation on the grounding wires and see if corrosion has seeped into the wires strands themselves. If it has, replace the wires.

Poor grounds are one of the most overlooked causes of many electrical problems.

 

[milojasper]

I've had this same problem. Never figured it out. When it got warmer, it fixed itself.

 

[amalik]

****, when did we get spammers here?