Working on mad old nuggets can be a rad time that leaves you with a real sense of satisfaction when you find and fix the problem you've been confronted with... but sometimes there are jobs which confound even the smartest, most experienced Mechanical Wizards.
Intermittent faults, those problems which pop up seemingly at random, are often as fun to successfully diagnose as drilling a third nostril in your own face. Then, once you start doing what seems to be a simple job, it turns out you have accidentally embarked on a massive mission involving half-stripping the car!
As Marty found out in THIS recent episode, his Super Turbo needed a new fuel pump. After removing the rear seats and trying to get access to the pump from above he stumbled across the first common frustrating job: having to drop a large part of the car out to access one common part. He'd have to disconnect and drop the fuel tank out the bottom of the car. Spew.
Once he pulled the tank out (which was thankfully a much simpler job than the brain pain he went through with his MR2 - video HERE) getting the fuel pump changed was a straightforward job... until it came time to fire the car up and it wouldn't run.
Replacing the fuel pump in your car is pretty simple, but take some time to check the polarity on the wires running to the pump to avoid the problem Marty had where his fuel pump ran backwards (which would make it a fuel suck). While it was an easy problem to fix, finding the problem and working out what caused it took bulk time Marty could have spent eating delicious burgers.
Triple-checking your diagrams are correct (or are for the correct model they claim to be) could have saved me about 3 full days when trying to discover why my car didn't start. As it turned out the file I'd saved was incorrectly labelled and was for a different model whose ignition switch was wired a different way.
For older cars checking wiring plugs for intermittent faults is a good idea as the plastic gets old and brittle over time, which means the system isn't getting constant electrical connection. The metal pins inside the plug can wear out, or get loose, which again causes intermittent faults. The same goes for vacuum lines, which can crack (and leak), internally collapse (and then pinch shut when the engine is on), or swell, but you might not be able to see these problems when the car is not being driven.
Going over your car regularly with a thorough over-and-under inspection is a great way to pick up problems before they cause issues on the road. It's also a great idea to go over your car before heading to the dyno so you don't end up wasting time and money fixing simple things you could have sorted beforehand. Also, Marty should have picked a better time to argue with Tuning Fork over whether vinegar or Chicken Salt is better on your hot chips. Leave dyno time for dyno-tuning, kids!