I have a 1991 240 that won't start at all now. It cranks and turns over fine but never 'catches' -- it was running fine and then I had this happen to me intermittently for about a week, but a new fuel pump relay seemed to fix the problem (for a few days) but the exact same thing started happening again. Now it won't start at all -- just cranks.

The fuel pump does not buzz with the key on. I read about the ECU being bad about not grounding the fuel pump relay causing this problem, and I found a used '951' Bosch ECU on ebay for cheap, so I bought it, plugged it in, bought a new relay to be safe, and it does the exact same thing.

I can get the fuel pump to come on (can hear the buzz) by connecting the #4 and #6 fuse so I assume the fuel pump isn't bad. I have a multimeter and tried poking around with it, but its pretty damn hard to figure out.

I *think* I'm getting 3.5 volts through the 30/85 wires on the fuel pump harness with the key on, but I'm not sure. I do believe I'm supposed to get 12 volts through those two wires. I kinda just touched the metal connectors of those two wires at the harness to the multimeter probes, and it read 3.5 on the 9v Battery Test setting.

Anyway, I have no idea what to do next. Does this sound familiar to anyone?! Any advice would be great.

 

Does the pump purge for a second when you turn the key on but don't crank?
I'm assuming you spun the fuel pump fuses around when jumping them and all. Could just be corroded...

 

Trying it this morning, the pump does 'come on'/'purge' for 1-2 seconds with the key on. I did spin the fuses -- they look clean.

 

Make sure fuse 6 is clean. I would make sure you have good spark from one of the plug wires.

The bad fuel ECU's tend to be mostly isolated to the 1990 model year, with a "pink" label.

 

If the pump runs momentarily when the key is initially turned on, then I doubt it is a fuel issue. Like Bubba says, look for spark.

The next place I would check is the Crank Position Sensor. This is located on the top of the bell housing where the engine and transmission mate. It has a wire that runs up to a connector located on the firewall. Check this for cracked/frayed insulation.

The ECU uses the signal from this sensor for timing the ignition system. Without a signal on this, the engine will not generate spark.

Good Luck