We are baffled. Have been working on an m42 swap into my '76 for over a year now and the damn thing just won't start. I have had some threads over at r3vlimited that offered suggestions but nothing that has stuck yet, so I am reaching out here. The FAQ is much more active.
We have spark, we have fuel, we have excellent compression. The engine is timed properly. Every sensor ohms out fine. The wiring harness has been pinned out repeatedly and everything matches. We have tried two different ecus, two different crank position sensors, two different cam position sensors. The car has coil on plugs (because the spark plug wires that came with the car were busted), its got brand new coils. Injectors are the common ford four pintle injections that were rebuilt prior to purchase. They all seem to spray properly. Fuel pressure is in spec. Coils are in proper order 1-2-3-4 from front to back, we have tried other orders that some people have sworn work. Relays all have power, the power seems to remain constant throughout cranking.
The car cranks and wants to start but won't. Last week we replaced the crank pulley and it made a noticeable difference. Now it gets even closer to starting and backfires and pops and gurgles and sometimes even seems to start with one rev before dying. Below is a video though the phone doesn't pick up the sound that well.
One thing that has bothered us, and is possibly the cause of this, when we pull the coils and watch them spark (in slo mo video) they stop sparking after a few cycles (of wasted spark). It just seems to stop sparking completely. We would think this has something to do with the crank position sensor or the ecu but as mentioned, we have tried to ecus (both supposedly from working cars) and two CPS, both new, both ohm out correctly. We are definitely at the "throw parts at it" stage of troubleshooting. Right now I have an AFM on the way (though supposedly it should start with this unplugged, so we have tried both ways), and another (used) CPS (this one is a different part number, the original part number that was later superseded).
The r3vlimited threads are here: http://www.r3vlimited.com/board/showthread.php?t=384330 http://www.r3vlimited.com/board/showthread.php?t=391672
Video of a start attempt here: https://goo.gl/photos/ZGRHB9xRmQ8WfcrX7