94 RAM 2500 quits abruptly at highway speed when fully loaded after about 50-60 miles. No problems when not loaded. Changing the coil enables re-start. Later, putting old coil in and it starts and runs fine. This has happened 3 times - everytime I pull my boat. Whats up?

 

how many bad coils are we talking about ? 1 or more?

it may be something else, such as crank position sensor, cam position sensor (aka secondary pickup coil), ASD relay, Fuel Pump relay, Fuel Pump.

when it quits, do you loose spark at the spark plugs, and/or power to the coil, and/or power to the fuel pump relay? if all of these it indicates and ASD shutdown.

 

This has happened the three times I was towing my boat (about 7,000 lb all up) but never hapens when driving without the load. The truck cranks after it quits and the tank fuel pump runs, but no spark. As soon as I change the coil we are off and running again. This happened yesterday and the weird thing is that when I got home I plugged the coil in that I had remeoved and the truck fired right up. Checked both old and new coil for primary and secondary resistance and they were the same - about 1.1 ohms on the primary and about 10k on the secondary. If it is the ASD it somehow resets when I change the coils. If it is the crank or cam position sensor it somehow "heals" quickly and why would this happen only when the truck is hauling a heavy load? The dash temp gauge is showing normal temps. I replaced all plug wires and the coil wire with new the first time this happened.