Random hard starts mkII

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Engine history:

Full rebuild 18,000 miles ago (over bored with new pistons & valve job)
New glow plugs & wires installed at that time.



This car will sit for 1-2 weeks at a time, I usually only drive it on weekends.
The other day, after sitting for a week, it started normally in the morning. I stopped at a store <1 mile from my house to get a coffee. Came out <2 minutes later and it wouldn't start.
I suspected the fuel solenoid was stuck, because it just started fine just minutes ago from a totally cold engine.
So I checked it and it made a faint clicking when voltage applied.

I cranked and cranked in short bursts until it finally started, with a cloud of smoke from all the unburned fuel in the cylinders.

It idles and runs great once started.

The next few times I drove it there were no problems.

Then I had the same no start problem about a week later, again after starting just fine from a completely cold engine.

I started to suspect some air in the system or faulty glow plugs.

I didn't test actual amp draw, but I know that at least some of the glow plugs are working.....for a quick test I put my fluke meter on the glow plug buss bar and got a big voltage drop for 5 seconds on a cold engine. (from 12.5 to 9 volts, returns to 12 after 5 seconds)

So my next theory is air in the system or injector bleed off....but this theory isn't supported by the fact that it always starts quickly when cold after sitting for a week.
The only consistent pattern for when it wont start is that the engine was warm and had just been running.
Any ideas of what else I can check for? (dont say compression)

[Trumper]

I had the same issue on a fresh rebuild. I swapped over to a Ford solenoid to turn on my glow plugs for like 4 or 5 seconds and never had a problem again. If it is good and hot....no plugs needed. If it is low to moderate warm....it wants a few seconds on the plugs. Runs like a molested gazelle. It will test/try to destroy the ligaments in your shoulder, elbow, and wrist if you try to turn over with a wrench.

Get rid of the glow plug relay system.

[Fatmobile]

It might seem like the starter is turning it over fast enough,... but commonly when the engine is hot it's tighter and more difficult to turn.

Next time it happens; unplug the glow plug sensor wire.
The glow plugs won't light up when it's warm,... add a little glow and it should start.

Disconnect power to the pump and crank it for awhile.
Feel for warm/hot cable ends from the battery to the starter.
Feel the starter posts, feel the ground cable ends.
Hot/warm spots means bad connections.

Plan B: get a bosch premium remanufactured starter.

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Well it happened again today:

Started normally after sitting for a week. Glow plug light came on for 5 seconds.

Drove about 2 miles, parked for half an hour. Came back, no start. No glow plug light. Lots of cranking.

Opened the hood, hooked a jumper wire up to a glow plug and directly battery for about 5 seconds. Got back in, and it started on the first crank.

So Im about 99% sure its the GP sensor or relay. I think the engine temp is just warm enough to prevent the GP's from coming on, but they are really needed ( like Trumper suggested).

[Fatmobile]

Just disconnect the wire from the glow plug sensor.
Blue/yellow?
It's on one of the waternecks coming from the head.
The glow plugs will always come on,...
but I still think it's a lame starter or cable connections.
You'll find out when the cold weather comes.