Engine hard starting after setting few hours

As a follow up to this....not surprisingly, my starting issue got progressively worse to the point even advancing the throttle 50% would either not work or the engine would start, die, and then be flooded/unstartable for hours. Had to limp back to dock 4 times in a row on 1 engine. But then it would start the next day. Although this year, the worsened condition now requires 50% throttle advance for cold starts also.

Fast forward...my mechanic/friend and I replaced the injectors and the engine coolant temperature sensor on my problem engine. In the process, we did tests to verify the fuel pressure regulator, iac, tps, and map sensors were all good. Further, on both engines, we're working with fresh oil, fuel filters, plugs, wires, caps, rotors, and pcvs. The moment of truth...fire up the bad (SB) engine and the problem is still there; needs a throttle advance.

We then swap ignition coils. Try to start. Same story.
We then swap the computers (ECMs)...and the issue switched engines!

So....does anyone have any experience with weird engine issues caused by the ECM?
Does it usually require replacement? Or is there some other common culprit in the form of loose connections, poor ground, corroded contacts? Any guidance how to attack this? If the ECM wasn't $3200, I'd just replace it.

Thanks!

Probably Mefi 3 ? There is repair service available for some of its failures. OBD Diagnostics is good.

Yes MEFI-3. And yeah, was planning to call OBD today. Will also call my dealer and Mercruiser to see if it can be re-flashed. Was thinking i should try contact spray on the pins and connectors in case of corrosion. Not likely the result of faulty ground (or other) wires, given the problem followed the ECM swap.

My buddy just had that same problem. He thought it was the ECM. Turned out to be a bad ground on the fuel pump. The engine is running like a top now. He cancelled the purchase of the ECM. Hope this helps.

Thx...That would make sense if the problem didn’t travel from SB to Port when i swapped the ECMs. SB is magically healed now and Port suddenly has the starting issue.