what could be wrong with my 1989 Buick Regal?It will only go 15 mph .
on 1990 Buick Regal

I have a 1989 Buick Regal 3.1,last year I changed the fuel pump and fuel pump screen , and it ran fine, now this year it started missing real bad, so I changed the plugs and plug wires and it ran fine for a bit then it started acting up so I put a new air filter in it and fuel injection cleaner in it and its still acting up only will go 15 mph and then dies , after about 15 min. I also had the catalytic converter checked and its fine and the fuel pump is working to, so please what could be wrong with it this time?

2 answers
Have any trouble codes? Tap test MAF or get it tested.
mass air flows are a common issue in this yr