Had the same problem on my 240. Thought at first it was the external pump. Replaced the intank pump and the external punp. The external pump was a aftermarket non Bosch pump. The car wouldn't run at all then. Put the old bosch pump back on and the car ran fine. Some thoughts on the intank pump. If the float snaps into the sending unit arm and is not real tight, make it tighter. If the float comes off when your putting the sender/intank pump unit back in the tank, it can be a bear to get out. On my 240 the float came off in the tank and took some time to fish out. The thing wants to float to the back corner and is hard to reach. I ended up after retrieving the float tacking it in place with a small dab of JB Weld. Seemed to hold it in place. If the intank pump is not working the external pump will be noisy. Sometimes the intank pump will also be noisy. If replacing the external pump buy a bosch unit. The intank pump is an AC pump I belive.