so i’m fairly stumped on what is going on, the car has left me stranded twice, and forced me to push start it.

so preface: car is 07 Si, has a brand new battery. had been having this slow crank/no start issue several times but it has always either resolved itself or i’ve had to push start the car to get where i need.

today it started, drove around all day. went inside and came back out to start it and it slow cranked/no start. i take the battery and have it tested, it tests bad so i install a brand new battery. car starts completely fine, started perfectly 5 times in a row. i go to put my tools up, and attempt to start the car to move it, and it slow cranks/no start. what the f… so i pull another vehicle up and attempt to jump start it. same deal, slow crank no start to an eventual no crank no start. absolutely like the battery is dead, so i put my meter on it and it’s showing 12.6 at the battery.

i checked the trans and frame ground, both are clean and tight, but after it rains i’m going to recheck both and make sure they are extra clean.

i’m debating on throwing any cash at it because it just doesn’t make any sense. i don’t understand why jumping it off won’t allow it to start. this issue usually happens after it has been drove. yesterday i drove 60ish miles and stopped for less than 6-8 minutes to get gas, and it wouldn’t start. i don’t feel like it’s the alternator because it appears to have no issues charging while running, it has a smooth idle, no dimming of the lights or anything that would indicate to me that the alternator is failing.

any help would be beneficial, i have a 7hr trip i have to take on sunday, so i have minimal time to figure this out. thanks to all who read and reply.

 

Check your charge harness... it is not uncommon for the main starter power wire to get corroded/rotten and limit current flow. Check the wire at both ends looking for green/dark/corroded copper wire... the positive battery post junction is the likely culprit.

 

i have also noticed that when reinstalling the battery terminals, there is no spark at the battery. it’s literally like there is no ground.

 

starter turned up to be bad. removed the rad support and gave it a few whacks and the car would start. couple key cycles and it would not start, few more whacks and it started again. also all the comments about the knock sensor were correct, it instantly broke when i went to unplug it.