Back in high school we (the guys in auto shop) would sneak out and replace a buddy's coil wire with a piece of like booted vacuum hose. It got to the point we all carried our coil wires in our pockets during school.
I was "in competition" with a really sharp, and fairly experienced fellow student at the school I learned auto repair from (Los Angeles Pierce College). He worked as a part time tech at a local Texaco station, and he was really good with his diagnostic approach. We were friends, although with what I am about to share you may well wonder how that could be... heh heh... We were in the same tune-up and engine diagnosis class, as well as some other classes. Sometimes we had live cars with real issues to work on. Other times we worked on shop mock-up engines on engine stands with the necessary wiring and plumbing to provide for electrical and coolant needs for when those engine were running.
Well, one day we had no live cars to work on, and the instructor had to leave for a little while. He told us to just work on the mock-up engines, introducing problems for other students in our group to diagnose, in a kind of an ad-hoc round robin manner. So, we all got to it, introducing various problems then moving onto the next engine to diagnose what was done to it as another group was left to figure out what we had done to our victim engine. My Texaco friend was in the group following me. I happened to have a can of spray graphite in my tool box for some reason. Making sure he was busy working on the engine I had previously already disabled electrically, I removed the black distributor cap and sprayed some graphite inside the cap, then put the cap back in place.
Well, he found the problem with the prior engine(s) pretty quickly, which did not surprise me in the least. One of the kids in my group had seen what I did, and he said, "I bet you never find what 's causing the problem with this one!" I would have preferred to not have anyone say anything, but the hook was set and it was game on. So, we got through our next diagnosis quickly enough, but my Texaco friend and his group were pulling out every trick in the book diagnostically, but they were bewildered. They tested the ignition coil and it has plenty of juice to create a spark. The spark plugs were all clean. There was fuel, they checked and even swapped the distributor rotor. Our instructor came back just as the class session was over. It was my last class for the, as well as for Mr Texaco. But he normaally went to work after this particular class. He was beginning to get frantic as his group disbanded due to the class being over for the day. "I know it has to be something simple," he said. I told him I had nowhere I had to be and would hang out to help if he would like. Nice guy that I was. About 15 minutes later he asked the instructor if he could use the phone to call his employer to tell him he was going to be running late. Man, I felt like such a heel. This guy was as committed as he was confounded (and good). Before he placed a call I told him I was certain he would never find the problem unless he just began to swap parts. At that it would be the last part he thought of. I showed him my can of spray graphite and pointed to the distributor cap. He looked perplexed. I took the cap off and ran my finger inside the cap and showed him the graphite residue on my finger. "Dang! I would have never thought anyone would do that!" We had a good laugh and he headed off to work. I figured some day I would pay handsomely for that dirty trick. No harm done, all in good fun, but I am still waiting for the shoe to drop.
I do wish I had kept in touch with him. He was one hell of a nice guy. And full of his own kind of tricks.