Odd sudden loss of power

[Westy78]

Coming back from a camping trip this afternoon and climbing a long steep grade I had a sudden loss of power and lost all throttle input. I was climbing a long grade at 55mph indicated (so more like 52) in third gear. It had been around a minute or two at this speed and rpm when all of the sudden the engine lost all power and the throttle had no response. The engine slowed and stalled. This was all within a few seconds. No noises, shutters or strange feelings. I shut the key off and coasted to the side of the road. Went back to check on things and saw nothing out of place. All wires tight and in place, throttle cable intact (this was my first thought as that is what it felt like, a broken cable), all plugs tight. Went and tried to start it back up and it fired up and ran perfect all the way back home including another hill climb and a run up to 60mph in third.

During this loss of power head and oil temps were fine and oil pressure was normal. This is a Camper Special engine running a Mallory Unilite distributor so those high sustained rpm are easily doable and have been many times before. I have no idea what could have caused it. It seemed electrical as it was like a switch was thrown when the power loss occurred. Did I hit that mystery ECU rpm cuttout, hot coil, freak AFM malfunction?

[Randy in Maine]

Anything weird going on inside the distributor cap?

[dtrumbo]

Double relay ground? I had a similar thing happen on our trip to Disneyland. Fortunately I was given a clue. When I changed lanes and crossed the Botts' dots (lane marker bumps) was the onset. Coasting to the shoulder and crossing the rumble strip "fixed" the problem. This was my clue to a loose connection. My symptoms were exactly as yours. Everything perfectly fine, then everything perfectly not. Totally binary. It turned out to be the little brown ground wire that was tucked under the mounting screw for the double relay. Over time that sheet metal screw wallows out the hole it self-tapped 35 years ago. I moved the ground wire to one of the screws that holds the "gray wall" to the body (only removed twice, once when I accessed the fuel tank two years ago and again to tuck the ground wire under it). Problem fixed and never returned.

I hope yours is as simple.

[Jivermo]

That same ground wire was a bugaboo for me, also. It took me a good while to track it down. Nice lesson, though.

[Westy78]

Thanks guys for the suggestions. I haven't looked under the cap yet and I'll give that ground wire a look. The relay could have vibrated loose during this summers many forest service road miles.

[Amskeptic]

engine lost all power
fired up and ran perfect all the way back home

Consider it an anomaly. A global shut-down like that suggests starting way up the chain at the coil (+) supply, double relay to fuel pump supply. A momentary short at the reverse light fuse to clip kills the coil and double relay.

I had a choke wire on the Road Warrior touch the throttle cross-shaft bracket once. Killed the engine for ten seconds. Almost as if there is a auto-reset breaker on the ignition circuit. No blown fuse or anything. It just killed the engine, then it re-started after it had cooled down.
Colin