This is driving me crazy, heres whats happening:
68 390 c6, I take it out a few times a week down the road and when it comes back to the garage, temp gets up to about 200-210 at idle... it runs down the road at about 190. As soon as I shut down, I try to restart and it turns very slow once or twice then...click...click. If I put a charger to the battery for about 2 minutes, it will fire right up very strong, shut off, and it starts just fine...again and again it starts fine. Only does this when I bring it back from driving and it heats up, but it never overheats. Here is what I have changed:
...new starter, ford o.e motorcraft
...new high crank motorcraft battery, 1000 cranking amps
...new motorcraft alternator
...new motorcraft voltage regulator
...swapped aluminum 1 inch carb spacer for 1 inch phenolic spacer to avoid vapor locking
...wrapped the starter in heat wrap to prevent heat soak
...timing is set by ear,vacuum, and tach...not sure where it is yet, but does not ping. I know if it is too far advanced it will cause the starter to drag, so getting a timing light to verify timing is next on the list, but would assume it would do this at all temps if advanced too far.
...running premium gas
Heres the biggie... the battery is located in the trunk. It is grounded to a very thin piece of semi-clean metal in the trunk pan. All cables, positive and neg are 2/0 welding cable, BUT, there is no ground from the battery to the block. I do have a ground from the body up front to the alternator bracket. Is is possible that when the car gets hot, the batteryand the cables have to work extra hard to supply the current flow, causing an increase in resistance, enough to keep the car from starting. Then as soon as I hook the 12volt charger up, she fires right up and continues to start right up. Should the battery be grounded directly to the block, and will this fix my problem?? Any other ideas?? Thanks!

 

I was thinking a cable issue before I read the end of the message.

I think grounding to the block would be a much better idea...maybe you can find a way to test this idea using jumper cables or something before spending money on a 10' 3ga cable or whatever

-Gun

 

My guess is that your timing is right on the edge of just right and to far, probably 9-10 at idle. I set mine between 6 and 9 depending on the motor and the way the distributor is set up. The hotter motor will drag more when the timing is to far advanced. Also add a ground cable. The dragging is causing the starter to work harder which draws more amps and needs a better ground. sounds like the ground is not quite enough enough. 1 degree to much advance and not quite enough ground = hard starts when hot