Fuel injectors not pulsing; have fuel and spark

With engine cranking, do you have spark at the spark plugs? Do you have fuel injector pulse? I can't tell if that fuel pressure is initial prime or not? The initial prime doesn't need rpm signal, no cranking, after that the computer needs to see rpm signal. I saw what you replaced, I'd have to check wiring circuits before replacing anything.

Causes A code P0303 may mean that one or more of the following has happened: Faulty spark plug or wire, Faulty coil (pack), Faulty oxygen sensor(s), Faulty fuel injector, Burned exhaust valve, Faulty catalytic converter(s), Running out of fuel, Poor compression, Defective computer... Possible Solutions If there are no symptoms, the simplest thing to do is to reset the code and see if it comes back. If there are symptoms such as the engine is stumbling or hesitating, check all wiring and connectors that lead to the cylinders (i.e. spark plugs). Depending on how long the ignition components have been in the car, it may be a good idea to replace them as part of your regular maintenance schedule. I would suggest spark plugs, spark plug wires, distributor cap, and rotor (if applicable). Otherwise, check the coils (a.k.a. coil packs). In some cases, the catalytic converter has gone bad. If you smell rotten eggs in the exhaust, your cat converter needs to be replaced. I've also heard in other cases the problems were faulty fuel injectors.

could be a fault in the #3 injector wiring, with the engine running back probe the wiring at the injector with a led trouble light it should glow at each pulse. a pulse can be felt by holding the injector if you have no light. compare with # I&2.

How the computer determines a misfire is through a lagging effect in the crankshaft turning-when one cylinder is not producing power, the crankshaft doesn't turn as fast, and the computer senses it through the crankshaft sensor.
Misfires are usually a fuel problem, spark problem, or a low compression problem. Compare the spark at #4 with the other cylinders-all should have a blue, snapping spark. If good spark, check the spark plug -it might be defective. Compare the spark plug in #4 with the others. If it has a black sooty appearance, it is running rich-injector may be leaking. If the lower insulator on #4 is whiter than the other plugs, it is running lean, and the injector may be partially clogged, or not pulsing well.
If gas and spark is good, do an engine compression test. If #4 has low compression, it could be a valve problem, or worn piston rings, or a head gasket failure.

If it isn't pulsing right, maybe it is staying on all that time -and spraying fuel like crazy into your cylinders! Come on, Joel, a weak spark and injectors not pulsing right? Get a different ecm and plug it in. Then you can learn the circuits on your old unit and fix it in your spare time.

fuel lines hook up backwards problem solved...

Hello
Here is what to check let me know if you need help checking this out
most common misfire causes on the cars I've worked on have been:

1. Spark plugs
2. Spark plug wires
3. Ignition coil
4. Fuel injector
5. Wiring to fuel injector
6. Timing Belt
7. Vacuum leak or stuck open EGR
8. Contaminated fuel or bad fuel pump
9. Weak compression
10. Blown head gasket

It could very well be a bad coil pack,or you have low compression in that cylinder.If the compression is good then go with the coil pack,if not you may need a head gasket or an intake manifold gasket.

check the injectors on that bank for pulses.. a regular 12v text light will do it should flash when cranking... its very possible that the crank sensor or camshaft sensor on the replacement engine is bad and giving you all the problems you have now.. are you using the original injectors? if you have injector pulses then check the coil for pulses the same way.. btw make sure you have 12v to them even before cranking engine could be a bad asd relay..wet plugs on one bank would also indicate a possible leaking injector and basicly draing the fuel starving the oposite bank for fuel.. to verify that the rail must be lifted by removing all 4 bolts make sure the clips hold the injectors firmly and turn the key to run but dont crank it then look for fuel leakin from bottom of injector(s) any drips is a bad injector..

Is it fuel injected? Or carburated?
If it has a carb, did you clean out the float bowels and jets?
If it's injected, you may need to clean or replace the injector nozzles.
Fuel that has been sitting for 2 years can turn to varnish.

And after you replaced the head gaskets, did you do a compression check on the motor?