Help! 2006 Mercury 75hp four stroke EFI fried two computers??

[fishinmexico]

I have a 2006 Mercury 75 hp four stroke efi. It currently has 82 hours on it. I purchased the boat and took it out once for a 100 mile round trip ride with zero problems. I then took it out a second time and it started cutting out and died on me. I am in Mexico and the closest Mercury dealer is 5 hours away. I pulled the motor off the boat and took it down to the dealer. We found out that the injectors were staying open. He took the injectors out, sent it to the lab and had them cleaned. After he installed the injectors the same thing was happening. He looked around the motor for a ground but he did not find anything. The motors literally looks brand new. He put another used computer in and it solved the problem.

He said that he thought that maybe there was a ground in the harness. When I got back I mounted the motor and checked the harness. The harness also looks like it is brand new. I checked the battery cables and found that the old owner had extended the cables with a nut and bolt and taped it up with electrical tape. The wires were sitting in the bilge in some water. I figured that must of been the problem and mounted the cables up high in a dry cabinet. I hooked everything up and the motor ran fine at idle.

I took the boat out the other day to test it out. I made it a whole 300 meters and the boat did the same thing. When I got back I had a local mechanic come over and we found out that the injectors were staying open again in 3 cylinders. It looks like something fried the computer again??? Any help would be greatly appreciated on what could be doing it. Battery cables look good, motor looks brand new with the cowling off, harness looks new and so does the control. I did notice that when we were cranking hard on the motor that the negative cable did heat up a little bit.

 

[Fun Times]

Hi there, welcome to iboats!

Be sure the battery cables are clean and tight as a loose cable will cause the cable to become hot. It's not recommended to use wingnuts at the battery as they typically don't get the cables tight enough.

Be sure the charging system is not over charging the battery/electrical system.

Check the voltage going to both the good and bad fuel injectors and compare the two. Ohms check the wires between the fuel injectors and ECM.

Also just to be sure, In the following link below, try sending Mercury marine a message with your engine serial number to see if there are any service bulletins that may pertain to your situation of burning out ECM's. https://www.mercurymarine.com/en/us/contact/outboard-customer-assistance

http://simonmotorsports.com/ Might be able to repair your two ECM's

Hope you find something soon, good luck.

 

[craigrhoades]

I bought a 25hp efi fourstroke as part of a used boat package at the end of last winter and spent all spring trying to at least diagnose the source of its chronic cutting out, beeping and occasionally backfiring. Anyway, ended up I bought a repair manual. And as per the manual, if the problem is common across all cylinders, it's most likely the result of a bad or loose ground point. Turns out they were absolutely right. After a couple months of fuel system examination and component checking, I simply turned off the garage light, shut the door, started the motor, and spotted a tiny spark arcing across with the rhythm of its rough loping idle. Upon correcting the connection it went from rough as a cob to healthy and smooth. I'm not sure exactly how many ground points there are on one of these fourstroke efi's, but I can't overstress the adverse havoc a loose one can wreak. It'll literally cause all kinds of cutting out, beeping and backfiring. I just wanted to share this experience in the event it can help someone else.

 

[GA_Boater]

I bought a 25hp efi fourstroke as part of a used boat package at the end of last winter and spent all spring trying to at least diagnose the source of its chronic cutting out, beeping and occasionally backfiring. Anyway, ended up I bought a repair manual. And as per the manual, if the problem is common across all cylinders, it's most likely the result of a bad or loose ground point. Turns out they were absolutely right. After a couple months of fuel system examination and component checking, I simply turned off the garage light, shut the door, started the motor, and spotted a tiny spark arcing across with the rhythm of its rough loping idle. Upon correcting the connection it went from rough as a cob to healthy and smooth. I'm not sure exactly how many ground points there are on one of these fourstroke efi's, but I can't overstress the adverse havoc a loose one can wreak. It'll literally cause all kinds of cutting out, beeping and backfiring. I just wanted to share this experience in the event it can help someone else.

Thanks for the info. It's now part of the library.

Since this is an old, inactive topic, we'll close it.