Mercruiser ECM hour discrepancy-crazy puzzle for the experts

[hisa1111]

Hold on tight for this one. Same guy buying the 2002 Amberjack 290. Bay Test coming Mid-April. Here are the facts. Both engines are original 5.0 MPI and I verified the SNs on the blocks that match the original delivery document. Broker replaced broken Tach STB and it reads .5 hours. The STB engine has 504 hours per computer. Now... The Port Tach reads 504 hours BUT the engine readout shows 1000 hours. The broker found this out on their own and is trying to get the story from the owner. Original delivery date on boat 26-June-2002
Port ECM: W9000E41 4-25-2002
Stb ECM: VI00O6M1 7-15-2003
My bay test is in a couple weeks so my mechanic can compression test and see if the port engine shows that much more "wear". Is there any plausible explanation? OR should I run for the hills. The rest of this boat is amazing. Clean, B3s are great, Kohler Gen with 100 hours, etc, etc.

 

[LG111]

Maybe at one point the power to the port engine ecm had power to it that drove the hours up but not the tach. Still odd.

I have a simular situation but opposite. My tachs are the same at 900 now. But after adding VV Mobil on my engines I see all digital info. My digital hours are 526 on both engines. So how can that be unless 526 hours ago before me the ecms on both 8.1s engines were replaced. Or the tachs just run faster. I guess I may never know.

 

[KevinC]

Or maybe the ecm was replaced with an ecm from another engine? Does the ecm show serial numbers?

-Kevin

 

[PlayDate]

The ECMs have been replaced. The tachs have separate hour logging.

In regards to why.....lightning strike...bad owner wiring....a dozen things could have caused the previous owner to replace the ECUs. You may be able to track the ECUs back to the manufacturer with the serial number and see where they originally were sent to.

Even that won't help you make a decision.....a good survey with cylinder compression and oil analysis is your best bet.