Hey guys, been scrolling the forums a lot the last few days running down problems with this truck. It's a '98 with the 4.6L. It had a blown motor when it was given to me, so I swapped one out from a donor truck, was running when pulled. After the install, I've run into an issue where I've got spark, fuel and air, but it won't start and backfires from the drivers side exhaust manifold. I'm thinking it's the timing, but its always possible I overlooked something. Any help would be much appreciated.

 

Plug wires on wrong plugs? A timing problem should affect both sides, all plugs, equally.