I'm not sure what the voltage at the inertia switch should be but I have some suggestions and opinions(as always). I've heard some noisy fuel pumps and some exceptionally quiet ones, if the pump gets noisier it's headed for failure. Unfortunately quiet ones can also fail. Please reconnect or replace the inertia switch when you're done with diag, if you could predict an accident it wouldn't be an accident. They can be reset with no problems, 84 LTD wagons started coming in as no starts on Monday mornings during the summer. After a poor round of golf, the bag would get tossed in the back and the tailgate slammed hard enough to trip the inertia switch. We fixed them by showing the owners how to reset them and suggested they not slam the gate. Foreign cars and GM's at the time didn't have inertia switches and there were fires.
All I've got is a Haynes manual for 1993 to 2000 Ford Rangers and Mazda B Series trucks, and I can't find any reference to voltages to that Inertia Switch with key off, or on. Nothing in the manual about testing that switch either. I did find a YouTube video about generically testing an Inertia Switch (using a DMM), but I can't get to the male blade terminals and I can't get the switch off the firewall because Ford used what looks like a metric bolt that is smaller than 6mm and I don't have sockets or wrenches smaller than 6mm. Go figure.
I am beginning to believe the
Sporadic "No Start" issue is not that Inertia Switch. While this is my old seldom used "truck", nothing heavy is ever hauled in it in recent years, no golf clubs, etc and I think I've had the tailgate down only 4 times all year. Haven't hit anyone, nor my being hit. Previously when I suspected the Inertia Switch is when I had some grocery bags on the passenger floor and MAYBE a bag with 1 Litre soda bottle might have fallen over theoretically bumping the firewall, but I really doubt it. No sudden stops, this has happened before after driving it for hours on errands AFTER coming back home and it sits there overnight in the driveway.
This sporadic No Start issue has happened maybe 4 or 5 times in the last 18 months. A diagnostic nightmare.
Here's a brief chronology of this problem's history, keep in mind this 97 B-4000SE 2WD 4.0L V6, Auto Trans (same as a Ranger XLT) with only 100k Miles oddly exactly, never been in an accident-
1) This "No Start" the next day, or more, after driving it fine with many errand stops has happened 4 or 5 times before.
2) Other than the last occurrence 2-1/2 weeks ago, the truck would just decide to start with very little cranking to immediately! (WTF?) I was thinking a Vapor Lock issue. Again, on my B-4000, you can't hear the Fuel Pump from inside the cab, never could, too much sound insulation on the upper "SE" models.
3) The Last time 2-1/2 weeks ago, which I believe the Inertia Switch was tripped, though the button was NOT all the way up and I reset it and it started right up.
Coincidence?
4) I have had a long-standing issue with the Crankshaft Position Sensor, located on the bottom front of the engine where street crap (water, grime, dirt and dust) easily gets thrown up at it fouling the connector, maybe (I don't know) damaging or prematurely aging that sensor.
If, or can, that sensor become intermittently Flaky and inhibit the starting as I'm experiencing?
5) This truck has had an occasional problem with stalling from stops at stop lights, signs or turning at a corner from a stop. Started a few years after having the head gaskets done from an over-heating episode. I guess this stalling issue is possibly due to a vacuum leak somewhere causing a delay on the timing advance? I have no idea where to look for this leak, but with 23 year old hosing all over the place (I had to replace all the AC and Smog related hoses last year), the leaks could be anywhere.
SO ..... could this vacuum leak cause the No Starting issue Sporadically?
I did replace the Fuel Filter 2 years ago. When the truck runs, the engine is very strong, no hesitations and this 4.0L V6 in such a light Pup is damn fast. Every mechanic I've ever talked to says these Ford 4.0L V6 engines may be one of the best Engines Ford every design in the recent era. ( I wish I did have the later SOHC version though).
Again, I think the key clue here is it's been Sporadic.
Appreciate ALL the sound advice guys.