Dealership, if we don't know what it is, its the ecu.

And since we don't actually know how to troubleshoot anything, its often the ecu.

Hint. Its not the ecu.

 

A $1K experiment.

 

ECM was replaced and car did start, initially fixing spark issue, but was running rough.

Mechanic found that the fuel pressure regulator was leaking internally sending pressurized fuel back into the intake manifold through the breather/ recirculation hose on top of the manifold causing the fuel to pool in the cylinders and soaking the spark plugs causing a "no spark condition".
Cylinders were dried out and mechanic tested the system by routing the breather hose into a washer jug which allowed the vehicle to run smoothly.
He replaced the fuel pressure regulator causing the vehicle to run smoothly again without the cylinders getting flogged and drowned in fuel.

Car works again.

 

Did you ask for the old parts to be returned?

ALWAYS ask for the old parts. At very least, discourages them making up stories about parts bei bad that aren't.

Then you can swap them back and confirm they're actually bad.

What are the chances there were TWO separate issues that caused exact same symptoms, that occurred concurrently?

Maybe, and just speculating here, they changed ecu, THEN they actually started troubleshooting. Found actual issue, fixed it.

Whats weird is, you hear so many stories about cars serviced at dealerships that need ecu replaced, yet diy guys rarely run into bad ecu issues. Also, most of time they replace ecu, they end up finding something else wrong too. Hmmm.

They say car started after ecu swap, how do we know its true?

 

Given everything that OP tried within his own mechanical knowledge and know how, I'm actually more inclined to believe the dealer this time.

1. They got it started, which OP couldn't do.
2. The noted that it was running poorly and did something about it.

Could OP have fixed issue #2? Probably, but not without first fixing issue #1 to get the car started.

Congrats to OP, willing to share how much this set you back? $2500-$3000? Est $1100 for ECU and approximately 8hrs labor at $200/hr.

 

Correct, so all the old parts were returned with the car.
I'll check the ECM later to confirm if it's actually a brick or if it's usable for the future. It's not the worst part to have.

Correct, if I didn't replace the ECM I couldn't have gotten the car running again. Even if I did replace the ECM and the car was running rough, I probably would've run it even if it was running rough and not a sewing machine.
I try very hard not to fire the "parts cannon" at the car. : /

Est cost for a new Engine Control Module was $1100 (+ backorder time). A friend of mine had an ECM that wasn't the correct year for his vehicle but correct for mine. $0
Est cost for the Fuel Pressure Regulator was $170 (+ backorder time). I had a spare one from another one of my engines so I dropped it off in the morning. $0

I only paid for labor and yes it was about $200/hour but less than 8 hours. I'll note, the mechanic said he's owned three S2000's and from wha to could see in the parking lot, his S was pretty clean kept with some simple aesthetic mods. Always a good sign.

 

This might not have been the case for this guy, but something to check for if others have issues, but check your battery terminal connectors and make sure your battery is secured down tight. If there's any play at all in the connectors it could cause intermittent starting issues or no crank at all. Sometimes it'll seem like your immobilizer is messed up, but its the connectors. One of the cheapest things to check first.