Ignition gremlins

[Mbremith]

Ignition on my 70S starts to break down when it gets hot, I turn off ignition and back on then works ok, then a bit later starts to break down again and so on. Thought it was the CDI but put another on and does same thing, same with different coils. Any suggestions on cause? Everything is standard (MFI, points).

[classic]

Mitchell,

I'm not sure if the 70 was the same as 69, I'm away from my manuals at the moment, but my car has a relay connected to the start/ignition switch. Just a thought.

Just have a look under your dash to identify which relay in the trunk, behind your clock it is.

[Haasman]

Mitchell, if it were my car I'd very carefully look at the distributor cap and rotor. How long do you let it sit before restarting?

As an aside, when I have a heat related problem I always work from the greatest source of heat outwards. Engine=heat, type of thing.

[edmayo]

Measure the resistance of the rotor resistor both hot and cold. If more when hot could be the problem. Or just switch with known good rotor.

[Mbremith]

I don't usually let it cool at all, if it starts to break down (ie starts missing and wont rev) I just knock it in neutral, ignition off then straight back on and it works (for a while), although the hotter it is the shorter the period of time before it starts missing again and (eventually, as I found out on a VERY hot day) it doesn't work at all and I do have to wait for it to cool. Will have a good look at rotor and cap. Seems to me like an electronic part that slowly fails under heat load and is "reset" by turning power on and off which is why I thought was CD box but seems unlikely 2 boxes (one Bosch, the other aftermarket) would have the same issue?

[Merv]

Mitchell I assume you have tried those different plug leads and also the spare distributor cap? As Ed says check the rotor arm resistance. I have a spare I believe.

[Flieger]

You sure you have fuel pressure? The fuel pump (I think it is on the left side sway bar mount like my '71) is a bit close to the engine heat. Mine finally failed a few years ago. You can also have rust or other stuff clogging the fuel line in the tank. When you stop the rust falls off and you can start again.

[Jim Breazeale]

Still sounds like a CD box to me. Are you sure that the other CD box was a good one?

Regards

Jim

[ESully]

If no change with a different CDI and coil, make sure you have good fuel flow. I would also make sure to check the points contacts, dwell, and rotor are good, with no hairline crack in distributor cap.

[a356kid]

Does your tachometer act erratically when the car is misfiring or breaking up? Or have you noticed your tachometer not steady or jumpy? I just chased this problem on a 72 with injection. I also agree with Jim B. about the CD. I would check the contact pins on the CD and make sure they are clean and making contact. I would also check the screw-on or press-on terminals on both sides of the coil along with the soldered terminals. This was the problem on the 72 on which I was working. It is a clean well maintained looking that has had pretty work done to it, but not necessarily correct functional work. With this said it had multiple problems with simple wiring connections. The CD, the Coil, distributor, injection etc all looks good and is pretty but the simple connections were dirty and had been overlooked. The jumpy Tachometer is what lead me to check the connections on the coil. I just had the same thing happen when I was driving my Dad's Togo brown C coupe on Friday. The car after it was warm and on medium to hard acceleration would misfire and you could feel flat spots. Also on compression it would backfire as if it had an exhaust leak. I was at a gas station checking the oil and reached over to the positive side of the coil and the wire was on the terminal but it was loose. I crimped the spade and reattached the wire. The car did not miss a beat during the remaining miles of the 500+ mile trip. All this to say It may be something very simple.