Hi all,
I need some help. I just rebuilt the 400 in my Dads F350 Ranger and it runs rough. No sure what the issue is. 77 400 motor all new parts bored 0.030 over, new valves, new stock cam, new distributor, new plugs, wires. I had carburetor rebuilt 2 barrel. Intake has 13726548 as firing order. It acts like it’s not running on all cylinders. I pulled each plug wire off as it is running to see if makes a difference and found that when I pull off number 2 or number 6 it didn’t change the engine. I then pulled the plugs out on these 2 cylinders and found number 6 plug is wet and 2 is heavy black(fouled). I can see these two are on the same intake runner, so I am assuming with 6 not firing that 2 is over loaded. I changed the number 6 plug out to see if it’s the plug and got the same results when started..wet plug. Then I changed plug wire and got the same result..wet plug. Then I changed out distributor and got same result...wet plug. Then I changed out coil, no change. I then stuck a screw driver in plug wire to check spark to ground while running..and it is a weak spark not what I would have expected from an electronic ignition system.

What am I missing? Any help is greatly appreciated.

 

I would start with screwing a psi gage in each of those cylinders and see whats going on.

 

Hmmm. Did you brake it in? Might have had a lobe or two let go...

 

Thanks for the replies.... I found the issue. It was the electronic module box. I have never ran into that before, typically the module works or it doesnt.