91 240 Won't start - Fuel Pump Relay problems
#1
91 240 Won't start - Fuel Pump Relay problems
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.
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.
#2
#5
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
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
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