Mercury 200 EFI ECU question?

[puncho]

I took my boat over for service today, I have twin 200 EFI Mercury's, model year 2000. I was told that the ECU in the port motor has a short in the plug connection that goes to the wiring harness. What caused this bad connection was a result of the ECU plug unscrewing itself from the wiring harness. The Mercury dealer said that motor vibration had caused it to unscrew itself and was causing an arching in the connection pin which controls the fuel pump. They recommended that I replace the entire ECU, even though the motor still runs. They said that an ECU with a short could cause the engine to have a complete failure from not getting enough fuel etc... They also went on to say that Mercury had improved the wiring harness connection and ECU connection so that this would not occur in newer models. does this seem like good info? The motor which is said to have a bad ECU has run fine, now and then it seems to lose it's prime at idle. A quick squeeze of the fuel ball and the problem is solved. I don't mind paying $1,500 for a new ECU, but would like to know what you think. Any help would be greatly appreciated. thanks

 

[JB]

Re: Mercury 200 EFI ECU question?

Hi, Puncho.<br /><br />Welcome to iboats. <br /><br />I think this belongs in the Merc Troubles Forum. I will move it there for you.<br /><br />Good luck.

 

[rodbolt]

Re: Mercury 200 EFI ECU question?

hello<br /> it cant be shorted<br /> if it was the wire smoke would have been released<br /> the loss of prime is usually due to lack of periodid low pressure fuel pump maint. rebuild the low pressure pump. should be done every third year or so as a maint item.it is possible to seperate the wire from the connector and hardwire around it. in fact I have done it a few times. its a better option sometimes than ecu replacement cause if one pin is burned so is the other. if the high pressure pump fails or quits the engine dies so quick as to be almost imediate. wont be much slowing down. this can be observed with an analog voltmeter on the pump terminals and a fuel rail pressure gauge. hook it up and watch for voltage fluctuations and fuel pressure fluctuations. this aint voodoo nor black magic. <br /> without anymore running problem descriptions and based on the only problem is occasionally running the vapor seperator out of fuel I would say find a dealer that can handle EFI problems before they create one for you. if the VST has no fuel from the low pressure pump it runs out of gas. remember its kinda rare for the high tech to fail. normally its the low tech. squeezing the fuel primer has absolutely nothing at all to do with the ECU or anything else on that motor other than to refill the vapor seperator tank. period.<br /> good luck and keep posting

 

[puncho]

Re: Mercury 200 EFI ECU question?

rodbolt, thanks for the reply. The engine does not lose prime that often, just once and awhile, maybe like once every 3 months. Is it safe to say that either the ECU will fail all the way or could it have a shorting out problem that would intermittantly cause it to arch at the plug pin connection?

 

[rodbolt]

Re: Mercury 200 EFI ECU question?

an open may cause an arc. you really need to learn the difference between a short and an open if you wish to play. like I said. nothing you can do with the fuel primer bulb will affect anything electrical on that motor. believe it or not.<br /> if the connector is in decent shape do as I do and tape it after connecting it. if the pin arcs odds are it will momentarily shut the pump off. if that pin is actually the pump wire.<br /> if you have never rebuilt the low pressure pumps now is the time. they move almost 20 gallons of fuel an hour at WOT. they work they little hinnies off. rebuild them as a periodic maint issue not when its a dead motor issue.but this is only based on about 30 years of experience and more training than I care to remember sometimes. how and why did they dissasemble the connector? what were the symptoms that prompted them to look at the ECU connectors?

 

[puncho]

Re: Mercury 200 EFI ECU question?

That pin is the wire for the pump. The two mechanics were running my boat trying to figure out a rattling noise that I have been hearing over the last 200 hours. They did a complete compression check on both motors and everything checked out fine with powerhead. During a sea trial they stoped both motors and were unable to get the port motor to restart. After they removed the motor cover they said they found that the ECU conection to the wiring harness had unscrewed it self and that this was why the engine would not start. they screwed the connection tight after inspecting the pins and descovered that the pin that controls the fuel pump was blach from arching. The boat runs now, but they said there is no way to know if the ECU is damaged or not. He said the ECU could now have a short as a result of the lose connection. They recomend that the ECU be replaced.

 

[rodbolt]

Re: Mercury 200 EFI ECU question?

at a 50% mark up I bet <br /> that is normal for that part. does the engine exhibit any other symtoms of poor running other than the occasional loss of prime? and the fuel pump wire should be on the output side of the ECU so I would not worry to much.

 

[puncho]

Re: Mercury 200 EFI ECU question?

No the motor runs fine, I have never had any problems with that motor. I originally brought the boat in because I thought I had a problem with the charging system. Turns out the charging system was working fine, but they found this supposed problem with the ECU. The service manager even told me that, I could still use the boat with old ECU but that in the future it could fail. If I don't change the ECU could I damage the engine? could a damaged ECU cause the motor to run lean on fuel and blow a powerhead? What is the risk of total motor failure from not changing the ECU. Thanks

 

[rodbolt]

Re: Mercury 200 EFI ECU question?

hello<br /> in my opinion its not likely<br /> if the motor still turns up and runs correctly then the ECU is not damaged. they are fairly tough. normaly when they fail the fuel or ignition quits. I have never seen one with a partial failure. but I guess its possible. now running the VST lean due to a bad low pressure pump can destroy a powerhead. stupid ECU cant tell that the high pressure pump is out of gas. course the engineers never counted on lack of maint or air leaks or bad antisiphon valves. were it my money I would repair the fuel system from the VST back to the tank.. secure the connector at the ECU and black tape it to prevent it from vibrating. use of dielectric grease on reassy will prevent arcing.

 

[puncho]

Re: Mercury 200 EFI ECU question?

rodbolt, Thanks for all of your help. I went down this morning and talked to the mechanic, and wanted to see the ECU connection harness. The pin is a little black, but it does look like it needs to be replaced IMHO. I am going to put the dielectric grease on the connection pin and do as you said. When I pressed the mechanic and asked a lot of questions, I think he figured out that I had been talking to someone in the know, his attitude changed about replacing the ECU. He did not tell me I was crazy when I said I did not want to change the part, so I probably made the right call. Thanks agin for all the help.