No start, battery sparking at positive terminal. UPDATED

[Vortec]

I am finishing up a clutch replacement on my stepson's 2003 vibe gt. The engineers are sadists. I have swapped clutches on other vehicles (mostly RWD) in a few hours with no problems.

Anyway, I had my wife try to start it today while I watched underhood and when she turned the key it wouldn't start and the battery positive terminal sparked. No noise from the starter at all. I checked and the starter is getting full battery voltage and a signal from the ignition switch. Battery terminals are clean and I haven't found a bad spot in the cables yet. Normally, I'd just think the starter died, but the sparking at the battery makes me more concerned.

I'll check more stuff soon but had to call it a day. Any ideas are appreciated.

UPDATE: I got it running but now it idles terribly. Random misfires (code P0300). MAF data doesn't seem particularly odd but short term fuel trim is very high, at 20%. So I guess I'll be hunting for a vacuum leak next.

FIXED: The crappy idle was due to a vacuum leak in the EVAP system. I'd already replaced multiple hoses that were getting stiff but built a smoke machine to find the leak. It turned out to be a hairline crack in the vacuum valve on the back of the airbox. I epoxies it, put everything back together and it ran smoother than ever. We brought it back to my stepson last night. That's a 45 mile test drive and he's driving it today. Glad this is over!

[joatmon]

Wish I could offer some plausible explanation, but can't think of anything that would cause the battery positive terminal to spark when you turn the key to Start. Exactly where does it spark, from the battery terminal to the cable clamp, the clamp to the cables, just all over and random?

[Vortec]

The sparks are occurring at the battery cable clamp. It's arcing from one side of the clamp to the other. I've put my meter all over it and can't find a short, shunt, or bad ground. No bad fuses or relays.

However, to rule out a bad ground, I'll probably run a jumper cable from the negative terminal to the chassis after work.

[andrewclaus]

I'd clean or replace the cable clamp. There's resistance hiding in there somewhere, even though it's tight.

[Vortec]

I cleaned them thoroughly yesterday. No change. I am thinking there may be hidden corrosion and being moved around during the clutch job broke things loose inside the insulation. I truly hope it's that simple. If so, the jumper cable bypass should work.

[Vortec]

I only had a few minutes this evening to mess with the car. Ran jumper cables from the positive terminal to the starter solenoid. I was able to start the car but had to rev it some to keep it from stalling. I'm really hoping it's just a bad battery cable.