I'll get shot for this, but...
Our 88 Jeep Cherokee. Before anyone gets testy about it, yes it was a great purpose built vehicle, and the straight six would run forever. That being said... I spent more time wrenching on it than any other vehicle I owned.
It was a total mish mash of parts sourced from wherever, and while it was technically a Chrysler product by then, most everything was marked AMC.
It had the Renix fuel injection system that more or less gave no codes (everything was troubleshooting with a multi-meter). By the time I sold it, parts were becoming more of an issue (this system was only used on 87-90 4.0 Cherokees). On the flip side, I learned an awful lot about how fuel injection worked, since you had to understand what was going on in order to troubleshoot anything...)
The cooling system was a pressurized overflow bottle system and the bottles and caps were terrible, (Starting in 91, Cherokee's did away with this system, and I retrofitted mine).
In the end, it always seemed like about every 3500-5000 miles, something needed attention. Was happy to sell it at the end... It was becoming the epitome of JEEP - Just Empty Every Pocket...