-from opening up the valve cover and rechecking timing as you confirm tdc on cyl 1

-or removing the vaccuum pump, carefully, and looking at the position of the plunger (under pressure vs not under pressure)

I always prefer the valve cover story. my vaccuum pump gasket is too old but my VC gasket is reusable. (And checking the valves never hurts ;) )

Generally we unsecure one at the injector and watch for the dribbles there. Usually the easiest is #1 injector.

Can you hear/feel the action from the fuel cutoff solenoid?

Are you cranking with WOT?

Yes, I can hear the solenoid clicking.

What is "WOT?"

WOT = Wide Open Throttle. Holding WOT while cranking is an effort to get more fuel thru the system to purge air faster.

What's the best way to bleed air form the fuel system?

It depends on what tools and materials you have available, and your budget.

1.Temporarily plumb a low pressure (3 - 5 PSI) fuel pump upstream of the fuel filter. More PSI than that risks blowing out the IP seals.

2. Plumb a fuel priming bulb (commonly found on boat outboard motor tanks) upstream of the fuel filter. This priming bulb can stay there indefinitely without problem, which can be helpful for future system priming needs, i.e. fuel filter replacement or run out of fuel scenario.

3. Temporarily attach a Mityvac to the IP return hose. Pull vacuum until fuel flows without bubbles.

4. Simply cranking engine. Limit to 10 - 15 second bursts to avoid melting starter. May take several minutes. May not work if IP internal lift pump vanes are stuck, or if IP main shaft seal leaks.

5. Temporarily plug fuel tank breather tube, stuff compressed air hose into tank filler with a rag and inject air into tank to force fuel thru the IP. Probably works better to also disconnect the IP return fuel line and plug the section running back to tank.

6. Tow car in gear around the block. Works, but obviously only works on manual transmissions.

Crankshaft rotates 2x for each camshaft revolution, IP is connected 1:1 to camshaft so it is possible to time IP 180deg out relative to camshaft.

As RedArrow shared above, verify crankshaft at TDC, with camshaft #1 lobes pointing up & out, notch on IP cog pulley should roughly align w/ mark on IP triangular mounting flange.

I attached a Mity-Vac to the "out" return line of the injection pump and pumped about 2 gallons. Bubbles were present the entire time and are still present.

How long should this process take?
Does this indicate an air leak somewhere upstream of the pump?

If there were no leaks in the IP or upstream of the IP, and you pulled thru the return line, likely you could have purged air from the IP within a liter or two. Visualize the capacity inside the IP. You are pulling from the return line outlet, which is at the top of the top cover, so pulling out from the air space there while the fuel is entering via the fuel inlet, displacing the air.

We don't know enough yet to tell where the air is still entering from.
Some possible sources:
IP seals
Fuel filter
Fuel hose connections
Injector spill lines
There is also the possibility that the air is entering at the Mityvac hose connections or its capture cup, especially if you are going all out on the pumping handle and pulling high vacuums.

Does your IP have the transparent inlet hose? If you see bubbles moving along in there while pumping the Mityvac, that tells us there is air entering upstream of the IP.

The next step is to substitute some clear fuel line before & after the IP, and watch for bubbles at both locations while Mityvac-ing.

I just thought of another possibility-- you said the IP was rebuilt? It is very easy to reassemble the IP internals 180deg out so if the rebuilder wasn't paying close attention to the distributor plate pin and slot orientation to the main shaft key (can be easily fit together either way) then the IP can be 180deg out even when the external marks are all lined up... :eek:

But first let's get the system purged of air and pumping fuel out the injector hardlines.

That is an interesting thought, certainly possible.

This situation does sound from the running symptoms exactly like timing 180 off. Although I don't see where the external timing was verified yet either, so it could also still be off by just a few degrees somehow. If attention isn't being paid carefully to the position of the notch on the IP pulley flange, it's theoretically possible to set timing with the dial indicator to *any* cylinder's position, not just #1, right?

Agree the process described above by ngoma is the right way to proceed, expanding with a couple more thoughts here:

First, confirm the IP is pumping fuel (without air) and that fuel is getting to injectors. The method for this is to loosen at least one, or in my case preferably all 6, of the injector line union nuts, then crank the engine on the starter. You should quickly start to see fuel squirting out of all 6. If you do, then you're moving fuel just fine. I have seen it commonly be the case with a MityVac where air bubbles appear to exist but are actually just caused by the Mityvac tubing connections. So for now, IF you find you get plenty of fuel delivery to the injectors, I wouldn't worry about some air bubbles and move on to:

Second, confirm the engine is timed to .84mm ON THE #1 CYLINDER by doing the steps posted earlier to verify timing not just to the crankshaft but also to the camshaft (valve cover removal required). External timing is checked this way. If no problem is found with that, then there are some further tests you can do to figure out if internal pump timing is 180deg off as ngoma mentioned.

Since the engine did run at one point, I think you will find fuel delivery OK and the issue is timing.

Then, third and somewhat unrelated, you may still have some kind of issue going on with the starter motor or ignition switch, unless the overheated starter was just from extended cranking during an earlier attempt.

Found the problem, it turns out my timing was 180 degrees off.
That'll teach me to remove the cam cover and keep on eye on the lobes when I do the timing on the next d24, lol.