I have a 1984 volvo 240 GL LH2.0, that runs ok it will rev up to redline although it does have a rough idle it revs up.. well until about 10 min of driving and once its warmed up, it starts bogging and wont go over 2k and sometimes 3k rpm. Sometimes if i give it barely any gas it will rev up slowly but if i put my foot down the rpm bounces slowly from 2k down, i changed the fuel filter about 4 times in 3 months each time was dirty, i also changed the intank pump 3 times i also did drain the tank. i just swapped the motor / block kept everything else sensors etc, i was having this issue before my swap so its got to be fuel related, my main fuel pump is mostly loud sometimes alittle quieter, i have 2 LH2.0 mass air flow sensors i swapped it still same. My thinking is i need to change the tank or wash it out, and change the filters and pumps once more? maybe convert to a single 255lph intank pump?, and change the 02 sensor i have a aftermarket one in, as well as the coolant temp sensor? its currently not reading anything but i was having this issue with my old motor and the coolant sensor was working.
Any advice would help thanks.

 

One way that I can think of is if you can drive it SAFELY using a 5 gallon gas can as your fuel supply and temporarily bypassing the main fuel tank. That should tell you if the tank is the problem. Again, the key word is SAFELY.....

 

Yeah so basically I dropped the tank, it's terrible the car was sitting for 17 years so.. yeah it's a lot of rust etc in the tank, insane how this thing went 6k miles like that. Thanks for your advice