my car: a 1986 240dl

I am having an on and off bogging down on acceleration and what my wife calls a (popping) sound from under the hood. I can't find a descent volvo wrench in this city so I do a lot myself. I have recently replaced fuel pump, fuel filter, MAF, and catallitic converter. I am worried because I bought a cheapo fuel pump at autozone, and now the car will bog down (intermittently) when any serious pressure is applied to the gas, the problem is very speratic. Sometimes its fine, sometimes it will leave you stranded. I also hear a constant buzzing sound from behind the right rear tire when it decides to act up on me. Seeing as that is were the pump is located I am trying to find out if it is the pump itself or if the fuel isn't getting to the pump. Could it be the in tank pump not getting fuel out? or the outside pump not functioning. PLEASE HELP, this is my wifes car and I work 50+ hours/week so my time to troubleshoot is limitted and need to get this car running again. Thanks for your help...it is needed