Intermittent No Start - 5.3 L59 swap - Injectors Not Firing

[racecougar]

Curious if anyone here has experienced anything similar to this.

I swapped a 5.3L L59 into a '65 C10 back in 2017. The engine has been great, but it has an intermittent no-start that occurs about once a year, always when I'm far from home without any diagnostic tools of course. Here's what happens when this occurs:

1. The fuel pump primes for ~ 2 seconds at key on like normal.
2. The starter spins the rotating assembly as usual, but it's clear that the injectors are not pulsing. It's as if it's in clear flood mode. If you've ever cranked an engine with the throttle wide open you know that the cranking is audibly different/quicker.
3. Cycling the key, trying different throttle positions, etc., makes no difference.
4. After ~30 attempts, the engine will fire right up like nothing ever happened. It'll then go another year before doing this dance again.

So this happened when trying to leave a car show last night. I tried unplugging the DBW pedal, TPS, and throttle actuator one at a time while "trying everything", but to no avail. As usual, after a bunch of attempts, the thing fired up like normal, and I drove home. Diagnosing it this morning, I had a P0452 code for Fuel Tank Pressure Sensor Low Voltage. I have this DTC turned off in the tune file, so I'm not sure how that code was generated. Either way, I cleared it and it's remained clear today. I also pulled the elbow off the throttle body and had a helper operate the throttle pedal with the key on. At initial key on, the throttle blade opens and shuts once quickly. Pressing the pedal results in a pretty smooth actuation of the throttle blade, though I'd say that the actuator is louder than I expected. The strange thing is that pedal actuation with the key on, engine off, causes the tachometer needle to fluctuate. Video link below.

https://www.youtube.com/watch?v=v9WTzKA9L64

Any ideas? I don't expect this could be the crank sensor, as it would likely flake out while driving. From what I've read, if the TAC module determines an inconsistency between the pedal position and the throttle blade position, it won't fire the injectors, and made not generate a code. Most TAC module failures I've read about show up with the engine running; this truck has never had an issue when the engine was running. My only guess right now is that the actuator on the throttle body gets hung up with the blade closed once in a blue moon, and isn't able to move freely to verify operation at key on. That doesn't explain the tach behavior though. Any help/experience is appreciated greatly!

Here's a pic of the engine in question.
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[Jason Banks]

This is a tough/crazy one.

My first thought was go through the wiring for the fuel pump and make sure it is all good.

Is the power supply to the fuel pump relay fused or circuit breaker? If it's a circuit breaker is it good? A friend of mine had a bad one that would cycle on and off randomly.
Swap the fuel pump relay.
Check signal from PCM to fuel pump relay.

The whole Tach moving with the gas pedal, got me started thinking bad TAC module... then wanted to check where the Tachometer got its signal. PIN 10 on the Green PCM connector, and right next to it PIN 9 on the Green PCM connector is 'fuel pump relay control'

Kind of rambling, but that's where I'd check first, make sure PIN 9 and PIN10 on the green PCM connector look good and the wires are not making contact anywhere or the wires are not making contact anywhere. Maybe replace the easiest wire to replace.

I'm thinking even though you hear the fuel pump run, maybe it's not and you don't really have fuel pressure, that's why the crank but no injector fire...

[racecougar]

I can say that it is definitely not fuel pump related. You can clearly hear the pump prime and fuel return to the tank from the return line with every turn of the key. It receives fused power through a relay.

I had the "trunk" open when this was occurring, and had a helper turning the key while I listened, just to verify that all was good with the fuel pump.

Just to rule it out, I'm replacing the crank sensor with a new AC Delco unit next weekend.

Dad is also heading to the junkyards this week to try to find another throttle body, TAC module, and pedal (fingers crossed). My line of thought with those is to swap them onto the truck to verify that they work, then swap back to the current parts, and stick these spares in the toolbox. If/when this occurs again, I could swap these parts on and see if the problem is remedied.

The tachometer movement at KOER is definitely tied to throttle position. It doesn't do anything unless you're moving the pedal. I wonder if the TAC module is creating a noisy signal back to the PCM?

[Richard]

Maybe check the grounds. Engine to chassis, battery to chassis and ecm to chassis. Would also check battery cables.

[racecougar]

Originally Posted by Richard

Maybe check the grounds. Engine to chassis, battery to chassis and ecm to chassis. Would also check battery cables.

Done. If anything, I have more ground paths than the factory. ECM/TAC module/engine grounds are directly tied to the chassis and the battery; they do not have to rely on the chassis alone.