Hello just wanted to start this off by saying I have a 1990 Foxbody 5.0 with a 5 speed manual transmission. Was running perfectly fine but I decided to upgrade the spark plug wires to 10 gage and upgrade to an MSD distributor. I timed it to 15 degrees BTDC and was running/idling fine. I let it worm up before I took it out and was running fine. 2-3 minutes later I was in 5th gear and felt a big chug/misfire. I turned the car around and went home but had to keep the RPM’s under 15 hundred...

Missfire/chugging