All,

Details are important in order to rule out certain conditions.

Introduction
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I have an 88 Chevy Suburban R20 3/4 ton, 454 7.4 L, rear wheel drive. It has an obvious longevity and I have been driving it for a while. Yes, it has had a previous engine replacement over 5 years ago. I estimate the current miles at about 120,000. I have the typical leaks that a big block encompasses and I am attentive to address each leak as it happens. I drive it at most twice per week at about 100 mile round trip. I checked all fluids prior to my short trip.

The Event
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Sometimes I drive 85 MPH, but usually I am driving 65 MPH in the far right hand lane. I never drive faster than 85 MPH. Yesterday I drove on a short 33 mile trip and I was doing 85 MPH. The vehicle has been faithful for years.

However, suddenly, without a single sound to get my attention (no grinding, no sputtering nor anything abnormal) the Check Engine Light went on for about 3 seconds and suddenly all power to the engine driving the cylinders suddenly stopped (i.e. fuel flow meant nothing and the engine stopped operating). This has nothing to do with the battery. I pulled over to the far right out of the traffic and as I did so without engine power and navigating rear traffic, I coasted 1/4 mile until I reached the far right. Since this happened so suddenly and I was moving at 85 MPH this allowed me to progressively change two lanes safely and reach the outer side road area, out of any traffic flow. Notice that I did not state that I stuck the vehicle in neutral, but rather, under emergency conditions, I was able to traverse two lanes and then arrive at the side road on the far right while still in drive. The vehicle felt like it was in neutral even though it was in drive and a 1/4 mile coast was a minimal estimate.

So, not one strange sound occurred. No grinding. No snapping sound. Absolutely no sudden profound noise which I can point to. Basically, it was as if I had suddenly ran out of gasoline (which was not the case because I track miles every fill-up, not just depend on the fuel gauge), yet no sputtering, no jerking, and no stop-and-go surge-and-dying. The engine went from 85 MPH to off suddenly. When I did reach the side road on the far right, I waited for 1 minute and then tried to re-start the engine. The battery power and the starter were both engaged, but the truck would not start. I had it towed.

So, my suburban went from a nice cruise at 85 MPH, doing everything that I expected, to engine off in a fraction of a second, without any unexpected noise, and would not restart after finally stopping. It would be like just turning the ignition key to the off position while traveling at 85 MPH (yet no sounds were heard).

Ideas? (even if wild guesses)

Thanks

 

I'd start with the fuel pump.

 

I was thinking fuel pump or ignition module if applicable

 

OK. I replaced the fuel pump, cleaned the gas tank, ensured the wiring was properly conductive, and replaced all in reverse, including remounting the tank. The old fuel pump that was removed, rattled like two marbles in a bottle (broken).
*** Thank you INTHEBURBS ***
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So, I put in 11.5 gallons of clean gas into the tank and tried to crank over three times. Tried gain hours later. Tried again hours later. But . . . when I turn the key to crank there is crank, but no ignite. So, it seems I may have had a double failure. I started to think that the pump seized, which then rippled back to some component electrically.
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I pondered for days and . . .
A) Then I checked every fuse under driver dash and every fuse was checked for conductivity and all worked. Yes, I checked the ECMB Fuse and the ECMI Fuse and IGN Fuse.
. . . crank but no ignite . . .
B) Then I noticed two identical parallel relays mounted on the passenger side, inside engine compartment, against the firewall. I checked both with a brand new Relay.
. . . crank but no ignite . . .
Not being a mechanic . . .
C) Then I drifted toward whether there is yet another Fuse box. So, I searched the engine compartment. Could not find such. Maybe it is nestled somewhere???
D) Then I began to ask what is an ECM (Electronic Control Module) and where that darn thing is hiding. *** Thank you REDNUCLEUS, but is this the Ignition Module??? ***
E) Then I began thinking about what is called a Fuel Pump Oil Pressure Switch.
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So, I am thoughtfully researching and trying to learn, but need another nudge/hunch.

 

I believe ignition module and ecm are terms used interchangeably. In my 93 it's in the distributor and I am on my 3rd one at 340k miles.

 

check for spark with a spark tester. if you have spark at the plug wires, the ignition system is ok. if you do not...
test the ignition system
key in run, test for power at the positive terminal of the ignition coil using a test light. You should have power.
move the test light to the negative side of the coil. have someone crank the engine over. the test light should flash. this indicates the ign module is working properly.
ohm check the primary and secondary winding of the ign coil