I had my 1990 420SEL running great. Yesterday I was flooring it from a traffic light and as it was accelerating, it just shut off. I have idea why. It was driving perfectly and then all the lights came on the dash board and there was no power. i pulled to the side of the road and tried cranking it and all it did was crank (sounded different too than the usual cranking sound). I towed it home and started looking at it. It has spark. I tried spraying ether in the the plunger area and still nothing. I pulled the relay and jumped positions 7 and 8 and tried starting it and still nothing. It just cranks. I'm open to ideas of what to check next.

In the past 2 months I've replaced-

both fuel pumps

fuel filer

fuel accumulator

fuel pressure regular

cold start injector

cap/rotor/spark plugs and wires

new 02 sensor

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2022 Nissan Frontier Pro4x
1990 Mercedes 420SEL
1950 Packard 8

Previous German cars-
2001 Mercedes SL500
1983 Mercedes 300SD
2011 BMW 328i (manual)
2008 BMW 535xi (manual)
2006 BMW M3 (manual)
1980 Mercedes 300TD
2006 BMW 750i
1996 Mercedes E300D
1994 BMW 740i
2006 BMW 330xi (manual)
1999 E300DT Smoke silver/black 253k
2012 BMW 535i Xdrive M-Sport
1984 300TD-T 304k
1988 Mercedes 560SEL (parts car)
2010 BMW 550i xdrive
2017 Audi A4 Presitge
1979 300SD 313k
2003 E500 189k

1) Remove the fuel line from the cold start injector, and jumper the fuel pump relay. Does fuel squirt from the open line?
If yes, check that both pumps are running. If yes, then:
2) Remove a cam cover. Is anything obviously broken? Like the chain?
3) Was spark at the plugs or the coil? Is the rotor turning?

I'm going with Frank's second guess...sudden stop followed by a different cranking sound.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

UPDATE- I cracked the line for the cold start injector and the and when i turned the key fuel was spraying everywhere. So I know that it is getting fuel. The OVP fuse is good but I don't know about the inerds of the OVP. I am getting spark at the spark plugs.

__________________
2022 Nissan Frontier Pro4x
1990 Mercedes 420SEL
1950 Packard 8

Previous German cars-
2001 Mercedes SL500
1983 Mercedes 300SD
2011 BMW 328i (manual)
2008 BMW 535xi (manual)
2006 BMW M3 (manual)
1980 Mercedes 300TD
2006 BMW 750i
1996 Mercedes E300D
1994 BMW 740i
2006 BMW 330xi (manual)
1999 E300DT Smoke silver/black 253k
2012 BMW 535i Xdrive M-Sport
1984 300TD-T 304k
1988 Mercedes 560SEL (parts car)
2010 BMW 550i xdrive
2017 Audi A4 Presitge
1979 300SD 313k
2003 E500 189k

if it has the correct fuel pressure and spark, then it must be compression. pull the driver side valve cover and see if the chain has broken or jumped teeth on the cam gear. it can jump 4 teeth before bending valves. also, look for broken chain guides.