Maybe, just go through the connections and fuses and use Deoxit or some electric contact cleaner. Just to rule-out one hinky connection causing this misery.

 

I was trying to avoid some of that. I have Deoxit, I will spend a few hours and do a lot of unplugging/cleaning/inspecting.

 

Yeah, electric problems can be such a pain. I like to rule-out the cheap solutions, before diving down the rabbit hole of expensive ones.

Good luck!

 

It sounds like you've conclusively zeroed in on spark. It never has spark when you've checked that during no start events.

But to put final nail in fuel coffin, you said there is always fuel pressure, but you haven't actually checked to make sure injectors are injecting. My go to for ruling in or out fuel related issues is starting fluid. If it starts when its used, its fuel. Ifit doesn't, after repeated attempts and making sure sufficient amount sprayed, rule out fuel.

I suggest you still try that, just to put final nail in fuel coffin.

A question though, describe how you checked for spark.

 

I am going to do fuel pressure gauge so I can view while driving. Also I will try the starter fluid method. I have not ruled out that the injectors are working properly. If they are not working, I would again conclude it to be an intermittent electrical issue. I can't imagine all 4 electro/mechanical injectors working and then not working.

I have checked for spark a couple ways.
1) Pull #1 coil pack and plug. Ground the plug on the cam cover and visually check for spark while cranking.
2) I have a known working extra coil pack and spark plug. Unplug #1 connector and plug into extra coil pack and ground and visually check for spark while cranking. This is just quicker because I don't have to pull a spark plug and quieter. I have tested with other cylinders also.
3) Digital voltmeter with probes in the #1 and 2 pin on the coil connector. This is usually 3.5v when in a running condition. The meter does not react fast enough to indicate a spark this way so I abandoned that method.

 

Spark check method, have you verified its valid? Like made sure you can see spark when issue isn't happening?

 

After Winter I retackled the issue. Wiring diagrams/diagnostics kept pointing back to PGM-FI relay. I read my initial post and I had not mentioned testing the relay. The Mitsuba relay under the dash when you open it up has a circuit board and 2 relays soldered to the board. I had tested these relays early in my diagnostics and they were both OK. I stumbled upon a YouTube video: recently.

After heating up each solder joints to melting temp, I reinstalled the relay. I let the car run for a few hours in the driveway and there were no failures (prior the car would not run for more than 15 minutes at this point before failure). I drove the car a few times just putting miles/hours on it. I seemed to have found the problem. I ordered a new relay and replaced it. Since replacemet I have approximately 300 miles and 10 hours of run time. No failures so far.

Thanks to everyone that commented to help diagnose. Hoping this thread will help others.

 

I've found that manufacturers use RoHS (non-lead) solder in modern electronics. These solder points need more heat and don't flow like old-school lead-tin solder, this can cause connection issues.

Connection problems are usually fixed by resoldering the cold solder joints with 60/40 solder. I draw up the original RoHS solder with a solder wick and apply the 60/40 solder. I have fixed auto connections, stereos, TVs, and other electronics that exhibit intermittent contact issues. I also restore old guitars and amps.

My favorite solder is Kester 60/40, rosin core. I use a 0.062-inch diameter for most circuit boards. I still have my 1 lb spool, which I bought in the 1990s.