1991 Ford Ranger engine runs poorly

I have recently bought a 1991 ford ranger, with a 2.4 L engine, when I bought it the engine ran kinda sluggish, but I figured that is because it sat a long time, it drives alright and I replaced the spark plugs and spark plug wires about a month afterwards, me and my friend took the battery out to try to start another car, we put it back on and I tried to start it, and the battery sparked, and everything electrical turned off, so my friend cleaned up the connectors and tightened them down, and it started right up, but since then the engine has been running really sluggish, and acts like it doesn't want to go, if I push on the gas a little bit, its seems I kinda go, but the harder I push on the gas pedal, it runs really crappy, and will barely accelerate, if at all. I had some some people hook up a computer to it, and it said nothing was wrong, so the guy said that it was most likely the fuel system, I have replaced the fuel filter, and put fuel injector cleaner in it, and it ran a little better, but the engine still has no go. I've noticed that it doesn't not have a catalytic converter on the exhaust, and I have had a glass pack put on, I've heard that it might be running crappy cause it doesn't have enough back pressure on the exhaust, but I don't think that it would cause it run so sluggish, please help!