TR won't start sometimes

first of all check if it is a fuel or an ignition problem
when the engine rotates with the starter it is never a problem of the battery

 

There are, unfortunately, many single electrical signals that, if lost, will cause a US TR engine to crank but not start/run. You really need to determine if is is a spark or fuel problem as romano posted. Next time it cranks, but won't start, use a simple, inexpensive spark tester (or timing light) to determine if spark is present, or not, during the starter cranking.

One very simple thing you can do (assuming that it is a no spark problem) is to unplug/replug the 4-pin round connector (for the flywheel sensors) under the coolant expansion tank a couple/few times just to rewipe those connections. It's not a very robust connector. While you are there, wouldn't hurt to also unplug/replug the 2-pin individual connector for each flywheel sensor (although those are a much more reliable, robust type of connector).

 

Then borrow a timing gun and check for spark, it does not matter which plug wire, but check both banks. If spark is detected, start checking fuel pump relays. The odd thing is that it is like two separate 6 cylinder engines. It may stop working on one bank, but if it stops on both, there is usually something very specific wrong.

Last time that happened to me I was out of fuel.