Odd starting problem, (possibly) fixed...

[RotoFlexible]

After several years of infrequent and trouble-free use, my Elan became difficult to start the last couple of times out last year. Cranked OK, but took increasingly longer to catch. By the time I parked it for the winter it would hardly start at all. I did some troubleshooting before I put it away - jumpered the battery from a running vehicle (helped some), assured fuel flow to the carburetors - but finally put it in the garage to deal with in the spring.

I just took advantage of a couple of warm days to resume troubleshooting. The problem was still present - the best I could do with the battery jumpered was to get it running on two or three cylinders, once. Fuel was OK, I charged the battery and it seemed OK, static timing was good, checked voltage to the coil, pulled a spark plug and saw a spark (perhaps weak) while cranking. I removed the plenum cover from the carburetors (to get better access to the coil and distributor) so it was getting air. I replaced the plugs, checked the distributor cap and rotor. Nothing helped.

I was all set to remove the distributor to replace points and condenser when it occurred to me to try a different coil first. I found an old Lucas coil, cleaned up the terminals and changed the wires over. No change. I decided to check the voltage to the coil again, so I clipped a voltmeter lead to an open lug. Turned the key and - it started right up and ran well! What the heck... So the verify that the installed coil was bad, I moved the wires back to it, expecting the problem to return. But it started right up again.

So, I'm left with the conclusion that a bad connection at the coil caused the problem, and I eventually jostled things enough to make the connection better. But the connection wasn't bad enough to completely disable the ignition, just bad enough to weaken the spark considerably. That is a pretty strange failure mode. I was lucky to discover it before pulling the distributor. The car is running fine now, but I'll take a look at all the coil connectors and make sure they are sound.

[nmauduit]

I had a similar failure once, not so easy to identify with a high impedance electronic multimeter but eventually solved by pulling an extra coil wire. The difficulty is that contact resistance can increase (due to carbon residue or grit / oxidation...) then voltage is present but current limited. Typical at key operated switches, but also at weakened fuse holders (esp. when hot)...

[RotoFlexible]

Typical at key operated switches, but also at weakened fuse holders (esp. when hot)...

Good point. My ignition switch is original and it may be the culprit - simply coincidence that it decided to work again while I was fooling around with the coil connections. Probably time for a new one.

I recall a couple of years ago experiencing a brief (second or two) complete loss of engine power during which the tach ceased to register. A temporary loss of power to the coil would explain it.