I have a 98 Nissan Frontier and over the last year the power has declined significantly.?

I have changed spark plugs, wires, distributer cap, rotar, fuel filter, air filter and for a little while it was running great, but then the exhaust broke off right in the middle of the catalytic converter and i drove it for a little while like that. Then i welded it back together and now it seems like there is no power what so ever and i would like to find out the reason why. Any ideas on how to increase the power would be great.

It's a 1998 Nissan Frontier 4 cylinder 2.4 liter 4WD.I have a 98 Nissan Frontier and over the last year the power has declined significantly.?well your truck is absolutely gutless already i have the same truck 2 years newer and without the 4wd but more than likely when you welded it you didn't make a perfect seal and it needs that back pressure or else it will not run correctly can throw your timing off and misfire along with a handful of other horrible things. take it to get fixed proffessionally and it will be cured for good. those trucks are bulletproof.