Unusual MEFI -> N2K Gateway issue post engine pulls

echandler1971

I'll try to take all the details and make them short and sweet
1. 2 house batteries - parallel, have their own +- busses
2. House neg bus connects to port engine
3. Port engine connects to starboard and therefore, for starboard to make a path to house, it needs to go through the port engine.
4. N2K network off of house
5. Helm dependent on N2K data for RPMs and engine info - not much analog
6. Starboard engine data cuts out after starting engine. It cuts back in if I trim up or down
7. Both engines were pulled and put back last month.

This is a different grounding setup than I had. I was able to do some rewiring with the engines pulled and the grounding was terrible, so I replaced it all and changed the logical routing as stated above.

I've done a lot of narrowing down.
1. I connected the port engine MEFI gateway to the starboard engine and got the same results - it's not the gateway
2. It's not a connection/wiring/connector problem - paths are good and I can get data just by trimming up or down (odd, I know)
3. I get data all of a sudden if I'm trimming up or down, and then the data goes away again
4. I get data when the engine isn't yet started but it's keyed to pre-start
5. I get engine data (rpms) for a few seconds after start, and then goes blank

My theory is that the N2K gateway isn't feeling the ground from the starboard engine enough, and when it's running, there's something that causes the pathway to have "issues." And trimming possibly changes things? I cannot fathom how all that would interplay, but yet, trimming "fixes" it

So the question:
Is it ok to wire in a ground loop from the starboard engine to the house negative bus? Therefore, each engine would have a connection to house, AND, to each other via the crossover between them. The point being having a shorter path to the house may be all I need to make the gateway functional again (to be tested obviously). I hear negative stuff about ground loops, but nothing definitive other than "it can cause demons to pop up."

thanks

echandler1971

Drum roll please……………..

it was the trim position sensor. I disconnected it and magically the data returned! I don’t really use the TPS so I can deal with it at the end of the season. I either have the trim all the way up all the way down, as I use the trim tabs instead  

LaRea

It almost sounds like something's pulling down the supply voltage for the N2k network.  You didn't make any changes to the network, right?  

echandler1971

My network is fine. The port engine reads fine. It's only the starboard.  I just tried the loop - made no diff. Even switched to linking only the starboard to the house neg buss (pulled port engine off). No diff. It's not the ground from what I can see. Still, trim makes it work while I'm actuating. It makes no sense.

davidbrooks

Do you have a tool to be able to read your ECM? Rhinda? It doesn't sound to me like it's a grounding issue for the N2K network as it's working on one half of your systems that are connected to it. When I was first setting up my 2003 there were a few Gremlins that I had to figure out. The first one was that each engine had to be properly coded as port or starboard. I would double check and make sure that when they replaced the engines that they put the port engine back in port etc. Make sure that each engine is still coded properly. If all of that is still good then the other item you might consider is that the wire connected from the engine to the gateway could have some broken terminals or the wires themselves in that bundle could have gotten messed up. I found myself standing on that wire more than once and realized that I could have been causing some of the issues by putting undue wear and tear by just not having it properly routed.

Lake_Bum

Sounds like somehow the trim is grounding it out when not under power (trimming).  Is there any point where the ground is in contact with it?  

echandler1971

Lake_Bum said:

Sounds like somehow the trim is grounding it out when not under power (trimming).  Is there any point where the ground is in contact with it?  

The engine is well grounded. What I might try is to disconnect the trim motor just to see what happens and work backwards from there. The thing is, the port engine has all the same setup and a new transom assembly, but it's data is good and stays good. This is just all around weird.
That said, I re-read what you wrote and I'm going to do a continuity test between the new transom assembly and engine. Still, TA shouldn't have anything to do with this, but then again, here we are.

LaRea

Does the N2K network have an ethernet gateway?  You could hook it up to a laptop running CANview and check the data.  

echandler1971

LaRea said:

Does the N2K network have an ethernet gateway?  You could hook it up to a laptop running CANview and check the data.  

Yes, I have an ethernet GW, but the issue is moot in that regards. The Port engine GW is supplying N2K data with no issues. Furthermore, the foxmarine gateways have a bluetooth option to connect to their phone app, bypassing N2K, and the app isn't seeing data either, but only from the starboard side. The N2K network itself is fine. The issue is the MEFI data signal from the engine.  Recall that I also connected the Port engine gateway to the starboard engine and go the same missing data problem. I also connected starboard's to the port engine and the data issue went away (as expected). So, it's not an N2K issue - but it still could be a ground issue.

davidbrooks

I am going off the assumption you are running Merc's. If that isnt the case then ignore.  When you say you connected the port engine MEFI to the starboard gateway exactly what did you swap?  In my setup there were wires from both engines that connected into one junction box.  Did you try completely disconnecting the working engine.  Use ALL of the wires or components to the non working engine to see if that resolved the issue??   On mine i had an issue where the engines were interfering with each other and there wasn't a way to "Factory reset" anything without sending it back.  If you have digital trim sendors then your trim reading is coming from your ECM.  That is how it is on my current setup.  On my last boat i only had analog and had to put in seperate N2K sensors on the trim.  That doesn't sound like your situation.  If that is the case then it would either be bad harness from the ECM to your gateway or bad gateway.  I don't think this is a grounding issue.  These gremlins are frustrating.  I went through a very similar situation and spent hours trying to diagnose what was going on.  You also have the option to call Mercruiser.  They will walk through the process to read out power and impedance on each pin.  That was a little frustrating for me as the guy on the phone was at a level that was 2-3 levels above my education in using that multimeter.  He was throwing instructions at me and i kept asking him to explain it differently.  In the end.  I sent the parts back for replacements and it all started working.

echandler1971

davidbrooks said:

I am going off the assumption you are running Merc's. If that isnt the case then ignore.  When you say you connected the port engine MEFI to the starboard gateway exactly what did you swap?  In my setup there were wires from both engines that connected into one junction box.  Did you try completely disconnecting the working engine.  Use ALL of the wires or components to the non working engine to see if that resolved the issue??   On mine i had an issue where the engines were interfering with each other and there wasn't a way to "Factory reset" anything without sending it back.  If you have digital trim sendors then your trim reading is coming from your ECM.  That is how it is on my current setup.  On my last boat i only had analog and had to put in seperate N2K sensors on the trim.  That doesn't sound like your situation.  If that is the case then it would either be bad harness from the ECM to your gateway or bad gateway.  I don't think this is a grounding issue.  These gremlins are frustrating.  I went through a very similar situation and spent hours trying to diagnose what was going on.  You also have the option to call Mercruiser.  They will walk through the process to read out power and impedance on each pin.  That was a little frustrating for me as the guy on the phone was at a level that was 2-3 levels above my education in using that multimeter.  He was throwing instructions at me and i kept asking him to explain it differently.  In the end.  I sent the parts back for replacements and it all started working.

These are VP. I have 2 FoxMarine gateways connected to N2K off of the same multi tap. One runs over to port with its cable and the other, stb. As an experiment, I simply took the port’s mefi Fox cable and dragged it over to the starboard engine. I had the exact same cutout issues as the Fox device normally used for that engine. Therefore I ruled out the FoxMarine devices and N2K. 

I’m going to mess around a little bit with grounding though today. I’m gonna run just a jumper between the Grounding stud of the starboard engine to the metal case of the starboard FoxMarine . I also have the yet unused oil, pressure leads, which may be a combination of hot and ground, which may suffice for the same. I don’t think it’s the grounding, but there is a possibility that possibly the ECM is not properly grounded now after reinstall.
The other new thing I discovered when I took her out at high speeds, the trim does not make the day come back when the engine is at high revs. Otherwise, the engine still functions fine. It’s strictly a data issue.