Here's the short of it: I recently bought a 1980 242 DL, not running, but described as having a fuel problem. I replaced the main and tank pumps with used pumps from a salvage yard, jumpered the fuses to bypass the relay, and think I may have solved the fuel problem, but may have run into an ignition problem.

Here are the current symptoms, the history and details follow:
Engine turns and catches, runs smoothly for one or two seconds, then limps along on a very rough idle. I press the accellerator, and the engine runs worse. If I pump the accellerator, the engine will rev smoothly after a few pumps and a backfire, then returns to the very rough idle.

Here's the history. A friend who knew about my love for Volvos told me about this car that appeared abandoned in a parking lot. It has 158K on it (!?!) and has the cleanest body and interior I've seen in a long time. He suggested that if I was able to get a hold of the owner, I might pick it up cheap. To make a long story shorter, I did. After learning that the car had a fuel problem, I asked that I be able to perform one test: swap in my battery (from my 1985 244 DL), crank the engine, spray in starter fluid, and see that it runs. It passed with flying colors: the seller sprayed starter fluid, I turned the key, and I heard an idle so smooth that I felt lucky to score the car cheap. I paid my money, went to the DMV, and became the proud owner.

Three days later, I returned to the car hoping to diagnose and fix the fuel problem quickly. I confirmed that the main pump didn't run with the ignition on, went to the salvage yard, and picked up a replacement. It was a model pump from a 1985 244 DL, but I adapted it in by replacing the original banjo fitting and plastic fuel line with a new fitting and a short length of fuel injector hose. After installation, I could hear the pump whir when I turned the key on, but the engine would not catch at all. No fuel leaks.

Eventually I noticed that in the three days between the time when I bought the car and when I returned to fix it, someone had apparenly stolen the coil: I saw that the coil wire from the distributor wasn't connected anywhere. The vandals were able to pop the hood because the driver's window had been broken (I knew this when I bought the car). I salvaged a window, installed it, and locked up the car to return a couple days later.

When I returned, I installed a savaged coil. The car started, ran smoothly for 3 or 4 seconds, then stalled. I noticed that the main pump made a hissing noise, like it was pumping air. I figured the tank pump wasn't supplying the main pump with fuel, and replaced it with a salvaged pump. Same symptoms. I returned the salvaged tank pump, found a different salvaged tank pump, installed it, and heard that the main pump was receiving fuel. I also confirmed that the tank pump was pumping fuel.

Now the cars starts, runs smoothly for a second or two, then idles very roughly. I removed a spark plug, and the plug was wet with fuel and black in color. The four distributor cap contacts were black and pitted, as was the rotor. I cleaned the cap and rotor as best I could, but the symptoms did not change.

I'm tempted to swap out the ECU and/or the cap and rotor next, but have run out of confidence in a direction to proceed. I think I still have a bad fuel pump relay, but have confirmed that the main and tank pumps seem to work when I put a jumper between the main and tank pump fuses. Any suggestions?