Okay Bottom Line up Front:

2002 SS 3.8L -93000 miles Brand new battery - Measures 12.6 V - Duralast gold 700 CCA (Replaced yesterday because the old battery was dead)

Car is difficult to start - Turning the key to start results in one or two engine turns, dead silence, lights go out and then it either starts or gives another crank or two then starts.

Details - I have had some electrical problems since returning from deployment, and found somedays it would not start. I would disconnect the battery, reconnect after 30 seconds and the engine would start right up. I was thinking BCM or Passlock system. One day the car wouldn't start, and I did the battery disconnect thing, but no dice. I measured the voltage and got 10 Volts. I jumped the car and it ran. I drove around for an hour. I measured the voltage while running and got 13.75 volts. Turning the lights, Rear Defrost, Stereo and AC still gave me 13.75 volts. Turned the engine off; it would not start again.

Any time the car was jumped it would start, but would not other wise. I did some digging through the forum.
I ended up replacing the serpentine belt, it was badly worn. At the same time, I replaced the Thermostat due to a heating issue. (Deployments suck- cars sit to long)
I am hoping, I didn't put the thermostat in fully and a loss of pressure is causing the hard start...what I am afraid of is the starter is drawing to much current.

Anyone have any input on that?

Also, a friend (Not a mechanic) told me when you replace the starter you have to replace the alternator at the same time. I have never heard that before, but am no expert in car maintenance.

Thanks for the Help

Noboatfred

 

Check your grounds, but your alternator may be failing

 

Anyone have a suggestion for best way to check grounds?

I am not sure if I am doing it right.

Also, when the car is jumped with another car, or a booster it started right up. On the battery, with 700 CCA it is very sluggish sounding until it starts.

 

So I didn't find any grounds. After a couple of days of very sluggish starting, I couldn't get the car to turnover at all. The car will crank a few times, but won't start. sometime I will stop trying to crank it, and sometimes it will make a CLANG sound and I will stop.

I replaced the started this weekend. The car would not start because the battery was dead. I jumped the battery, and it started right up. I ran the can for about 45 minutes. The battery was putting out 13.8 Volts, with all the accessories, lights and such on. This morning, the car would not start. The starter cranks, but the engine will not turn over.

I jumped the car at about noon today, and ran it for 45 minutes. I checked the volts, and oil. Oil was a little low, but still within the normal range.
At 2:00, I tried to start it, and no dice. Does anyone have any recommendations of what else to check? Replace? Love my car and miss driving it.

 

I believe you have 2 issiues going on...
Your Monte has a lo voltage sensor that wont allow the motor to crank below a certain voltage/resistance. So as to not allow the starter to over heat and eventually fail completely... Despite the Battery voltage.... It could be the positive and negative battery cables could both be so corroted that its causeing the sensor to trip...So it woont Crank properly..Thus the intermitten startups...

Once you do get it running...You need to check the amount of voltage comeing from the alternator...

Since its been sitting for such a longtime...these are things that can happen over time...
With the connections at the battery... or the Corrosion in the battery cables them selves will cause the battery to not recharge...
Corroted cables and connections cause a very high resistance, Thus causeing starting, cranking, Chargeing issues..
You may end up haveing to change both the positive and negative battery cables. for starters. and hope this resolves it.
Maybe the lo voltage sensor is also faulty or corroted?

Hope this helps...

 

I did continuity checks on the wires - and the battery cables were good. All resistances less than .04 Ohms.

A friend suggested that despite reading 14VDC at the battery while in run, that the alternator may not be working correctly, and to remove the negative battery cable while the engine was running.

I thought this was a bad idea?

After days of exhaustive research through the forum, I keep reading about the BCM.
Is there a definitive way to isolate BCM or Alternator? I don't want to spend the money on a new alternator, just to turn around and take it to the shop for a new BCM.

 

I think removing the cable while running is a bad Idea. It was fine to test an alternator like that on an older car but a modern car has too many sensitive electronic systems to do that. Maybe the alternator is failing or starting to fail. Also look around for any chewed or frayed wires under the hood, maybe something got in there when it was parked.