Heyo, I've been having this issue with my 1970 Cutlass Sedan for a while. It cannot start on its own, but with a jump, it turns right over. Without the jump, it cranks once or twice and then nothing. The battery is good. I disconnect it every time I park it. And I just replaced the alternator. Once it does start, it runs perfectly. I was thinking it could be the starter solenoid, but I'm just not sure. Any ideas? Hoping it's nothing electrical.

 

You state the battery is "good". What is the measured resting voltage of the battery? What is the date code of the battery? Good doesn't get you far without numbers to back it up. What is the measured voltage of the battery w/ the engine running?

 

12.7 resting 14 running. Just bought it around 5 months ago.

 

Those are good numbers. I'm thinking maybe resistance could be culprit. Obviously, you'd like unimpeded delivery. Evaluate the most likely suspect(s): Battery (-) terminal cable to engine block. Ring terminal should be bright shiny & clean. Attachment point at block should be sanded, wire brushed or the like for best solid contact. Evaluate the (-) battery cable to block with some detail. Any suspect areas of the lovely blue/green oxidative discoloration. Sometimes it doesn't hurt to take a razor blade & open the rubber insulation to evaluate that cable about 6" on each end.

 

You may take the battery and get it load tested. If that checks ok and it’s not bad or dirty cables, then the starter may need rebuilt or replaced.

 

You are judging it to be a "good" battery because you bought it5 months ago. You need to get it load tested as Oldcuttlas suggested.

I had a battery that was bad and less than a year old.

 

What is the battery voltage while cranking ??? sitting there with no load on the battery does not tell you much. You need to test this under load. suggest testing with a load tester. If the battery passes the load test then I suspect the starter. Jumping this you say it starts, so I have seen starters needing just a bit more voltage to crank over.. My money is on a weak battery !!!.

 

Check for corrosion and tightness at all terminals, especially the starter. I have actually had two starters so bad, one had a brush holder cutting into the armature, needed boosting at the end, actually killed the battery. The other was a shitty out of box Summit mini starter, it got so bad it would not boost at the end. What cranking amps is your battery?

 

Or, check the voltage drop on the positive and negative battery cables before you do anything else.
i had a similar issue with my car and it turned out there was a total of 3.5 volts of voltage drop on the main cables. I took them off and they were crappy aluminum core cables. I replaced them with 1gauge copper cables from american auto wire and problem solved. Look on the net for how to test for voltage drop. Good luck.

 

^^^THIS! Also verify that the contacts and disk in the solenoid are not pitted.

 

It's the battery, have it load tested.