To begin with some history. 88 Grand Wagoneer 4.0 400,000 km. Runs great doesn't use oil. PO had overheating issues. He changed rad, water pump,thermostat, HG, the head. He gave up and sold it to me for 100 bucks. Turns out the rad cap was buggered and the block needed to be burped.
It seemed to be running cool for me so I changed the thermostat just to be sure. In the process somehow the MAP sensor hose came off.....took a while to find that. When he changed the head he didn't get the manifold tight. With all the barking and spitting it did the manifold gasket started leaking which made it bark and spit some more.
I got a new gasket and installed it. As I was putting in the last manifold bolt I look down a d see the manifold is cracked I at least 2 places. I drove it home from my friends shop like that. Cracked manifold and no pipe on donut flange. It ran just like new except really loud and low on midrange torque. So now I pull the manifold get it properly welded get new manifold to pipe studs and install the exhaust pipe. To get the rusted mess out I had to cut the pipe about 18 inches from the donut. It's getting all new exhaust here hopefully this week.
My question here is now it starts and idles perfectly dead nuts smooth BUT as soon as rpm hits about 1400 under load it bucks and spits until about 2200. It's ok under harder acceleration but not right. You can hear where about 3000 she starts to come in tune and really pin her ears back and flat out goes. Is it just the short exhaust screwing things up or do I have something else going on. It's a second vehicle so it's not a #1 priority for money. I just don't want to dump an exhaust on it and have it still not run.