I've been diagnosing the 'crank but no start' issue on my girlfriend's 3rd gen 3.4. It's been a 2-year project altogether so I'd love to get it started soon. After getting the engine professionally rebuilt and dropping it in, connecting everything and filling with fluids it will crank but not start. It also makes a pop/bang noise periodically while trying to start, which actually shakes the motor a bit.

What I've done so far:
--swapped starter from other truck with the same engine (definitely one that works), no change
--made sure crank sensor was receiving 100-300 rpm thru OBDII while trying to start
--tested all fuses with a volt meter to make sure the circuits are receiving power
--made sure battery is good and fully charged
--drained old gas (sat for over a year) and put in 5 gals new gas
--changed fuel filter after draining old gas
--tested all 6 spark plugs one at a time by holding them against metal, they all had spark. 5 out of 6 spark plugs were wet with fuel
--Just turned crank pulley to TDC mark and made sure cam sprockets were lined up to their marks. The cam marks weren't absolutely perfect but the correct tooth was about 2-3mm off which I believe is close enough

The fuel pump whirs to life when key is put in and I was able to use it to drain the old fuel, so it does work. I'm not sure the pressure or how far fuel is getting in the system though. The popping from engine is very strange too. Any tips would be great!

Compression all good?

Are the spark plug wires on the correct cylinders?

Ok, so plug wires are correctly routed. And the cams are a hair off. Something still seems off. Are there any pending codes or codes stored? Does the pass side cam sprocket have the nubs for the cam sensor? Probably can't see the crank sprocket but are all the nubs for the sensor there?

Worst case you might need to remove the pass side valve cover and see if the cam gears line up? There should be 2 dots on them. The rebuilder could have phased the cams wrong.

This thread will get more views too.

Spark plug wires are routed correctly
Compression test will probably be my next test and I'll post my results

No pending codes. Before having the engine rebuilt I had a P0420 that kept coming up, I'm guessing that was due to a large crack in the exhaust crosspipe causing a leak. My friend welded that up and since then no codes are present since I keep unhooking the battery. But I haven't gotten it started since then either

By nubs do you mean the actual teeth on the cam gear? I believe the shop replaced the cam gears and crank gear so they should all be there but I'll take a look. I've heard of people missing a tooth on the crank gear but this one is new

Yes, they are little nubs that trigger the sensors. I truly hope it is something simple, and not something internally. I think you can install the cam sprockets backwards.

I'd maybe look into doing a leakdown test on each cylinder to see if the valves are to tight and not fully closing causing the intake backfires.

I too had similar issues as you are minus a rebuilt engine, doing a 5vz timing belt/water pump. But it was my mistake + being mentally and physically exhausted and crossed up the plug wires.

Silly question, are the coil pack connectors fully plugged in? Connector lock tab not broken?

I'll look into a leakdown test as well, never done one before. Would a compression give me any clues or is that mostly testing the health of the piston rings, seals etc?

The connector lock tab is broken on one of them yes. When I put it together I snugged it up as much as it would go and used a small piece of gorilla tape to hold them snug. It looks just like the others but doesn't give the satisfying click

ETA - do you have a obd2 reader? Does the scan tool see rpm's?

Yes a compression test would tell you if the valves are sealing or not, its more of a general health test. Or if there is a issue with the rings (put a little oil in the cylinder and re test, if compression goes up its the rings). Leakdown test will tell you if it's the rings, head gasket, or valves. You will have to put each cylinder to top dead center (use a small wood dowel in spark plug hole to find top dead center).

If you hear hissing air from the throttle body, it's intake valves, hissing air at the tail pipe, exhaust valves. Hissing air out the oil fill cap, rings. Bubbles out the radiator, head gasket or cracked head/block. Here is a vid on how to do the test:

https://youtu.be/8yuCHzqH7MY?si=XRGnitPtmPHtD_p1

Yes I have the obdII with live data, while cranking the rpms go up and fluctuate between 100-300, so the crank sensor is getting data. Thanks for the info, this is what else I've done before looking into those tests:

--Tested MAF connector's resistance and made sure its voltage fluctuates when you blow air into it, like it shows in the manual
--Cranked engine while fuel rail bolt was a bit loose, fuel shot out in a geyser
--cleaned the 3 engine grounds I could find and tightened again

Have you sprayed some starting fluid in the throttle body while cranking to see if you get a hit? The motor moving while backfiring seems to lead to a timing issue I'm guessing. I'd suggest removing all timing covers and verifying all timing marks are correct. Leak down test is better than compression for all around diagnosis.

Right on, yeah I did spray some starter fluid a few times in small bursts while cranking, no luck. I'm going to look into doing a leak down test asap

Living in a small mountain town it will take a bit of time to get a hold of an air compressor for leakdown test. In the meantime I was doing some electrical troubleshooting using the FSM. This truck definitely has a parasitic drain of the battery so I thought that and the 'crank no start' could be related.

Under the symptom of 'no initial combustion' it said to first check voltage at the ECM wiring harness beneath the glovebox. I tried sticking sewing needles in the terminals to make a connection with the multimeter but couldn't get a reading this way. Does anyone know a good way to get a voltage reading in a wiring harness like this? I attached a couple pictures to show what I'm talking about

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Sewing needles w/alligator clips are great. Small paper clips work in a pinch too, but can damage pins if not careful. Do not ever puncture the insulation of the wire.

You can get a fancy set of back probes that works wonders.

Update:
I did some electrical testing using the FSM and everything checked out. The ECM was receiving voltage and the starter was receiving voltage too (thru ECM harness) while cranking.

The timing marks looked good but I took some photos cause I'm curious about the passenger side cam sprocket being a tiny bit off (last 2 photos). I don't think they need to be 'perfect' but wanted to get a second opinion before opening up the valve covers. The crank gear and drivers side sprocket looked dead on

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Timing marks look fantastic! They are spot on. I guess next step is popping the valve covers off and checking the timing of the cam gears and valve clerances. I don't know where else to look.