Strange starter problem

[mat_fenwick]

My engine is really slow to turn over, won't even spin - just half a revolution at a time. Replaced the starter just now - still the same. I have a 2 month old battery, so I had ruled that out (also because it was the same hot or cold), and have bypassed all the leads to eliminate poor contacts. I have also put a booster pack on but no improvement.
I'm going back out to try and have a think, but has anyone any good ideas?

[DavidRutherford]

have bypassed all the leads to eliminate poor contacts.

Including the battery-to-engine negative lead?

Next thing to do is start checking voltages all over the place to ensure there isn't (or to find) a volt drop that shouldn't be there.

[mat_fenwick]

Thanks for the quick reply David! Spot on there actually...

I did bypass it previously, with no improvement, but a multimeter showed a high resistance (both in the battery to negative lead, and the borrowed jump leads I was using. Doh!)

[Kitch]

Thats exactly the problem I had, and as David said...earth leads.

To test it I ran a jump lead from the negative terminal to the engine, and a jump lead from the engine to the chassis. Fired straight up!

[mat_fenwick]

I'm feeling quite stupid now, having wasted £40 on a new starter...
What I had don was clip a jump lead to the battery negative terminal, and the other end to the starter bolt. It was only when I got a friend to crank over the engine with me watching that I saw the smoke 'escaping' from both the jump lead, and the thin negative lead to the body!

I'm still puzzled why it would suddenly fail - it fired up fine on the (frosty) Sunday morning, but a few hours later with the engine hot there was next to nothing. Spent an enjoyable half an hour trying to bump start it on my own in a flat motorway services car park.

I will replace the negative lead, and the battery terminal(s) too, ideally with something I can solder.