My bronco had a regular 5.0 in it. I have swapped it with a 89 mercury 5.0 ho. I used my old 5.0 oil pan, timing cover, water pump, manifolds, valve covers, fuel rail, injectors, upper intake and lower intake, all sensors, wiring, and ecm. The new ho has a different firing order but wont run properly with it. If I use the non ho firing order it will run better but not properly. I have lots of power but at low speed its got a dead miss and it idles like a car with a big stall cam and sometimes will die. Do I need the ecm for the ho or the 19lb fuel injectors that the ho normally runs. Or have I got other issues? The parts store say that they both call for the same distributor. I am thinking that my ecm wont allow the fuel injectors to fire with the ho firing order. I need some real advise. Every one said this was impossible to swap but I have came this far and have it running. Hate to turn back now. Could I cross wire my injectors to the ho firing order? I also welded the smog pump lines on the back of the block. Thanks for your time!