Volvo: Lack of Power/Poor acceleration, volvo 850 glt, accelerator pedal

Question

Hello Ray,

remember I had a low compression on 3rd cylinder of my 95 Volvo 850 glt with 150,000 miles this test was done on last March and I was using 97 octane fuel. later on I gave up using 97 octane fuel and started using 95 since July until the time I took the car to the dealer on Nov 20 last month.the compression test was done again and all cylinder compressions including the 3rd with the problem are ok.. all are 130.. the dealers explanation to this was the use of 97 octane was a wrong choice and caused many other cars to have problem too, not only mine.  I got the car's engine,fuel system everything checked and things are fine.. but I still have one problem, the car accelerates poorly, when going uphill there is loss of power. for example if I'm climbing a hill with a speed of 60 miles, the car would start to climb but then the speed will begin to drop and it drops until 25 miles, however if my speed is 70 miles or more and if I start climbing with this speed the car climbs the hill perfectly.. I believe to thing that the converter of this car might be the problem.. the revs between 1500-3500 are so poor the acceleration is bad too. also when going uphill if I press the gas pedal more when it lacks power or switch the transmission to Sport mode from Econ mode there is a rattle that can be heard from underneath of sterring wheel when I move my feet a little from accelerator pedal the rattle goes away.. do you thing my o2 sensor is faulty and the converter is plugged? there are also black deposits on the tailgate pipe and the car performs very well when first started in the morning and it performs well until the engine reaches normal operating temp, this also makes me thing this can be a converter issue? would you agree?

I need to tell you that the cars exhaust system the converter the o2 sensor none of them were replaced before and they are 12 yrs old. the fuel pump was also never replaced, I doubt the pump too.. there is also no problem in transmission to its fully tested too.I have ordered a catalytic converter(eastern) and will have it installed but I wonder if you recommend me to replace the o2 sensor before having the cat installed...because I was told if the o2 is bad it might have been the reason and it might damage the new converter too.. would you agree? its a very long letter I know but I need your help..

regards,

Answer
Mete,
Yes the exhaust could be the major player in all the lack of power, that will slow the engine by not allowing it to breath. Have someone scan the O2 sensor and see how they are wroking if they seem slow to respond and not giving good readings by all means replace them. II always do feel better knowing that the parts are new and should be problem free. Continue with the exhaust work see how the car works before doing anything with the trans and converter.