90 2.3 Ranger runs horrible
Hello everyone, so the other day i bought a 90 ford ranger off my buddy for dirt cheap. When he got the thing it was running decent, we changed the oil pressure sending unit and put the engine all back together and it started running bad. He said he plugged something in and it started running better but im not sure what he plugged in. The truck ran good all the way up till when i bought it. I went to his apartment complex and warmed up the truck, then proceeded to drive it back to my house. It was running great and all of the sudden the rpm started to rapidly drop and the trucks mph dropped as well. I was petal to the medal in first gear trying to get this thin to a parking lot going 10 miles an hour. The thing went from good to bad in a literal blink of an eye. I had my dad tow me back to my house and i did some research and came to the conclusion it was my cat. I did a vacuum test on the engine and wasn't getting a solid reading at idle, nor at a constant 2000 rpm. I unbolted the exhaust system and did the same thing, Rpm at idle wasnt stable but it was at 2000 rpm. I havent ruled it out yet but i dont think it is the cat, it looks like its been replaced. Next i chase the fuel pressure but im sitting on a solid 35 psi. The vacuum lines are all on and my truck isnt kicking any codes. The only thing left that i think it could be are the plugs or the fuel filter. I only checked one easily accessable plug and it looked fine but you never know. Any suggestions? Thanks for helping!!