Sudden Unexplained No-Start

Can’t say I know much but maybe that helps because I’ve found that almost every issue tends to be the easiest most obvious thing that we all over look. These engines run on compression. You said injectors are fine but that doesn’t mean there isn’t a compression issue elsewhere right?

What about @riphips suggestion of the water separator?

If it is a compression issue,it would be due to the starter not turning the engine over fast enough in this case.


Rock

Cranking is very good. New and upgraded fuel filter was installed after the issue began, and fuel is getting to the injectors. A proper bleed was done. Like I said, even the shop is stumped... They'll end up charging me more than it's worth to dig too deep. Everybody seems to be going for the low-hanging fruit (no offense to anyone! It's a reasonable start) but the basic issues like cranking rpm, fuel getting to injectors, etc have already been looked at. I'll have them take off a valve cover and make sure the valves appear to be operating. Speaking of which, are the lifters hydraulic or mechanical? If hydraulic, what would be the effect if oil pump failed (relative to the lifters... ignoring engine wear)

If its none of the mentioned issues, you must have lost compression somehow. The best way to check mechanical issues is a compression test or a leak down test

You could have a broken cam but I would think this would be rare. 6.0s break them quite a bit but that is a different animal.

OK... Shop opened valve cover... They said there is fuel vapor coming up from the crankcase past the pushrods when cranking and applying compressed air to the crankcase blows up as well. That would explain the vapor in the intake, since it would be coming through the crankcase ventilation system. Their thought is damaged piston. Any thoughts, oh great gurus? (and BTW, they also say about $2100 for an engine swap plus cost of engine.... That's not happening

$2100 seems a bit high to swap an engine in an IDI. We have people here on the forum who can do that in a day, pretty much alone.

Re the cost for installing new engine... Anyone know someone in south-central Connecticut that might be available?

I had an ignition switch go bad on my 86, it taught me that checking the 12 volts at the cut-off solenoid is only the first step, you need to check it while cranking to be sure. The bad switch had 12 volt in the on position, but would turn off the 12 volts while cranking. This drove me crazy for a time, everything else I checked said it should run.

I was just about to chime in with comp check.
Before you throw an engine at it, do us all a favor and pull both valve covers. Yeah, one side is a PITA. Move the rockers. Find any loose ones due to bent push rods?
By the time you get those replaced, the engine from Promar (?) might be an option due to the bearings being worn down from excessive cranking. My Promar engine is doing good so far.

How does the wiring harness look at the connection plug over passenger valve cover since it is an '86
Also check for burnt wires behind fuse panel forward of E-brake pedal

Don`t know about engine you are having issues with, but GM`s sometime the woodruff key shears off on the IP, causing a no start....
Just a thought

I had the same experience as Joe Mc. Truck would start and run, but would randomly die on me going down the road or sitting in the driveway idling. It would almost always restart though. Then one day it just wouldn’t. It would crank but no start. Ignition switch. Attached to the steering column behind the dash. Internal contacts had basically come apart because the plastic box had separated. It’s worth checking. I believe the part was about $20.

From your description, and you assertion that everything else is in tip top shape, the sudden appearance of the issue makes it sounds like it is electrical in nature.

If the electrical/ ignition switch checks out, I’d be PROVING the IP, compression and starter.

Compression check is relatively low cost.

Having the starter checked to verify proper operation is next. Lots of guys THINK the starter sounds good until they hear a new one. Starter should turn so fast it rattles the whole truck HARD.

IP and injectors are of course a big expense. Last place I’d go, especially since you’re saying the IP was just replaced. I’d be curious to know where the replacement pump came from if you actually got past checking the ignition switch and starter speed.

Here’s a picture of the actual switch. This item has driven many an old Ford fan absolutely bonkers!




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I would do a compression test and see what cylinder or cylinders are testing low. Then if the engine is bad find a used running one and swap it in.

I wonder if he ever got it figured out.....