Cranking No Start, Help!
 

Hi all,
I have a 1999 Ford Explorer that I swapped 2001 engine into. Both the old and the new engine are the 4.0L SOHC, old one just blew a head gasket and the lower milage engine was a better deal. So after plenty of late nights I successfully got the truck going, and took it around the block a few times. Started her up a few times to fix some small issues but she was running great!
First major problem I ran into though was my catalytic converters- had the car running around 15 minutes and all of a sudden they started smoking like hell, they were glowing red because they were so hot.
Starter her back up the next day and she ran like a charm for about 10 minutes until she cut out somewhat quickly. Tried starting her again but only a sputter and then it stalled. Since then it only cranks, but it cranks well.
So I started troubleshooting:
-Not the battery
-Not the starter (Just replaced it)
-Fuel Pump Buzzing
-Replaced Fuel Filter, fuel pressure at the rail is good
-Check for spark with old spark plug and wire to ground, spark is good
-Unplug MAF, no change
-Check all vacuum lines, ICV, nothing
-Check all the electric connectors for bent wires or dirt, all good
-Check that weird kill switch under the dash on passenger side, nothing
-Switched the relays around, nothing
-Check for injectors by spraying starter fluid in the butterfly, cranks, cranks, BOOM! Flame shoots out the intake. So... timing issue??
-Replaced crankshaft sensor with functioning one from old engine, nothing
-Replaced camshaft sensor with functioning one from old engine, nothing
-I haven't compression tested it but I figured it's fine since it was running so well earlier
-According to firing order diagram spark plug wiring is correct

The rest is beyond me honestly. I had a mechanic friend briefly come over and have a look, and he confirmed it to be ignition timing. It seems like for whatever reason, the valves are either stuck open on the intake stroke, are not seated properly, or the computer is firing the spark plugs on the intake stroke. I don't know really anything about ignition timing but I read that my timing belt could've slipped a tooth or two, read to check what happens at TDC or something but I don't know how.
I'm also wondering if those catalytic converters burned out my valves from getting so hot and now they don't work?
The SOHC engines don't have a dizzy so it can't be that.
Could it also be wiring or an ECU/PCM issue?
Am I missing anything?
Thanks! Getting so frustrated with this one, usually no starts are pretty easy :(

You took a chance swapping engines . Not always a good idea, since they change many things from year to year.
Suggest you drop exhaust and check for plugged converter.

Yeah I know I did for sure, engine codes are matching though. I'm about to do that next, but I've tried firing it with the exhaust unbolted from the headers and it still won't fire. Thanks for reading!

The converters getting red hot would indicate too much fuel getting into the converters and the converters working overtime.

I would consider doing a compression test and that should help eliminate some possibilities.
Were you able to get any codes, that might provide some direction ?
A scan tool to examine operating parameters would help provide info to a more specific area.

Didn't even think of that but you could be right it smells like burnt and unburnt fuel when I try cranking it. I'll compression test it soon. Quick update though, for a while it was sounding like it was just firing a couple of the cylinders but now it just sounds like the starter is spinning? Still the smell of fuel.
Also I've got a reader but the computer won't talk to me, no codes or lights .

So I have no compression on a couple of my cylinders.. is the motor done? I can take it back, its under warranty .

Generally when the converters get cherry hot it’s because of an overly rich condition or fuel saturation as cause for the melt down, usually accompanied with a flashing CEL as a warning prior to the condition/overheat. Being it was running good prior, and now has failed cylinders certainly could be due to high/exceeding combustion temps and pressures.
If the engine came from a Dismantler usually they comp test them, or run check if possible before removal. If it shows evidence of severe heat, you may be in for some arm wrestling..
If the comp test is accurate, It sounds like your in sorta the same situation as the old mil, needing at least a top end if the warranty claim doesn’t hold up...

The engine was running smooth but idling high and had little power, the head gasket has gone on it. But you're definitely right the arm wrestling got about a week left on the warranty, and these guys do not wanna give me my money back even though they know I'm right. So frustrating, but I know its their fault, car never ran more than 10 minutes at a time, drove it around the block twice, but theyre blaming me for overheating it, but there's no way. Gonna see what i can do but thanks guys