Lately my 1992 240 has been stumbling at start-up except when the engine is cold first thing in the morning. It would start and run fine, but as it fired up the exhaust shook enough for it to hit the underside for a second after catching. I replaced the knackered exhaust mounts today to stop the knocking, Feeling bruised but pleased with myself, I turned the key and it wouldn't start. Ran a wire between fuses 4 and 6, and it started right up. I carry a used spare fuel pump relay in the car, so replaced it and all seems to be well. My question is, is brief stumbling and engine shaking at start up a sign of a failing fuel pump relay? Is there any way to tell if one is about to fail? The stumbling and shaking appears to be cured...