I drove the truck, hauled a load of dirt with it. Got home, went to move it. It started fine, but stalled under load. Would idle fine and stall when put in gear. This quickly deteriorated into failing to start. I initially thought this was a no-spark issue (I did the old school, pull the plug, hold it to the exhaust manifold and look for spark. There was no spark at the plug).
I followed the video for troubleshooting no-spark on the 78 power wagon, and the troubleshooting diagram found here:
www.scannerdanner.com/forum/attachment/11814?download=1
This was superbly helpful to identify that it's actually a weak spark, and not a no-spark. The incandescent test light on positive and negative sides of the coil all behaved as expected with key in the run position as well as cranking the engine. At this point, based on the video, I replaced the coil because I didn't pay attention to the conversation about identifying weak spark. New coil in place, exact same issue. After this, I realized that the video discusses weak spark. While I don't have a spark tester, I tried to measure the gap the spark can jump at the end of the coil wire that leads into the distributor cap. While the spark does exist, it's incredibly weak, jumping no more than 1/16th, maybe an 1/8th of an inch.
The troubleshooting diagram linked above does say "if the crank circuit is not functioning, spark will be there but too weak to start the engine." Now I'm stuck, because electricity is like gibberish to me. I can see the components that are part of this system, but am unable to really understand how to troubleshoot where an issue may be in the crank circuit. Any help is greatly appreciated. Where to next?
