Hi,

Ok you have me to thinking with you on this.
I haven’t noticed if I see the tachometer move its needle while cranking.
The starter doesn’t turn the engine over all that fast. I suppose maybe one or two hundred revolutions in a minute? On my 91’ 240 the first mark is @ 500 rpm.

Now it does not move until after there is a hitting cylinder and it all speeds up.
I tried it and no movement until after it hits.

I suspect during cranking the voltage in the whole system is down around nine volts. Not that it means anything except the IAC opens faster @ 12 volts. That doesn’t mean anything either.
I’m just putting that out there to think or troubleshoot with on other things for clues.

The ICU is the start man for the beginning of stuff being turned on.
The sequence is very fast with the System relay being the slowest animal in the chain. I
t’s because it’s still mechanical and it is a relatively high current switching device. Fuel pumps being number one.

You are not mentioning any flooding or smelling fuel after several attempts so that has my curiosity up a little.
The tachometer is not a reliable clue.
The sparks you are getting or not getting are apparently not reliable.
So we are back to the ICU’s job.
It sends two signals that the engine is turning over.
One to the spark coil electronic relay and one to the ECU that turns on the System relay that on a 240 is an orange wire tied to the AMM and on to the fuel injectors operated by the ECU by grounding their coils.

So back to the ICU and that electronic relay, that is located on a 240, behind the battery of all places can be cause an intermittent fault. It fires the coil to make sparks by breaking the coils 12 volt from going to ground just like the fuel injector works
The ICU moves the timing around from information from the ECU. So they are talking to each other so together they are partners.

The only outsiders are things on the orange power wires mentioned and the electronic relay out there with working with the ICU all by its lonesome. The ECU gets no feed back and therefore no error codes.

If your spark is intermittent, at best, then I would want to blame that hidden relay. I have only had one go bad but the harness to it can be another option to cheaply investigate.

Get into wherever they hid it on a 900 cars and service that harness connection.
Check out of harness length as they may be a ground. A 240 has a ground wire near there but I don’t remember if it is interconnected. It hooks to a screw on a fender so I’m get after that kind of stuff.
Good but Old American domestic vehicle thinking was to use rusting steel for an electrical circuit to save wire and labor.
My first exposure to green insulated wires started with Hondas first 50 cc scooters.
A joke among bikers, but sad one was, that Harley-Davidson had check with the Smithsonian to make changes on them. Even Washing them made them run better. 😊

This is summer time and that relay has a great big heat sink behind it for a reason.
Every ten years I try to service the heat sink with a special heat conductive paste used on transistors.

Of course that helps the small pins inside the connection.
Some claim just pulling it apart and replacing it cleans the pins if you are dead on the road. But behind the battery leaves it in the “out of site … out of mind” category.

It’s worth a cheap shot but if it is truly a spark issue then that thing is THE middleman.

Kep throwing out what you are doing. It can’t hurt to educate this 240 man.

Phil