i just rebuilt the motor to a 4.6 stroker renix but now it wont run right it backfires and stumbles and pops out the rear like the timing is off but it is not. with the timing marks lined up and the distributer at the 1st spark plug its 180 degrees off so i fliped it 180 degrees and it fires up but does all the backfiring nonsence so i have redone the timing 4 times just to make sure i also have done a compresion test all the valves are opening and closing correctly the cps has been changed new wires new plugs new cap new roter what confuses me most is the fact its 180 degrees off with the timing marks lined up...

so here are things ive done a buddy of mine has a renix xj as well so we decided to swap a few parts to see if we could fix mine computer and ditributor map sensor have also turned the distributor one tooth at a time to see if could find the right timing but same issue

what i have and have not done on this build
pistons h802pc
cam stock
new lifters
reconditioned crank from 89 4.2 light crank
352 conecting rods
new melling oil pump
24lb injectors
cloyes double roller if it makes a difference

parts i reused all i did was clean them
head
intake manifold
exhaust manifold
throttle boddy

 

Im going out on a limb here, but did you check the firing order, there's no other wires that could be in contact with your plug wires, maybe crossing crossing a signal???? dbl check spark plug boots/ends???