View Full Version : Mefi Microsurgery and Cable tip for 99 Maristar

04-27-2014, 09:55 PM
Boat: 1999 Maristar Sport 230 with stock Indmar engine.
This is to document my experience with the MEFI 3 unit and the associated cabling. It's probably 10 years too late, but hopefully someone will benefit.

I need to give credit to at least two other posters who talked about similar situations that helped guide me to the solution. However, neither pointed to the cabling problem. One posted a schematic and the other posted a proposed solution (which i used)

Anyway, last summer on shakeout before my annual Lake Powell trip the boat did not start and so I brought it home. I'll not go through all my lengthy (unwanted) learning about the Indmar fuel injection system and consequent debug. The MEFI was dead. I learned very quickly that the MEFI 3 unit is obsolete and has not been built for many years. After removing the cables, I saw that the problem was that pin 1 on the cable receptacle had corroded off. Not good since that's the power supply pin to the unit.

Credit to another poster who soldered a bridge to another adjacent unused pin inside the MEFI and posted the solution. Here's some photos showing how it's done. However, this is not the root cause, nor is the placement of the MEFI the root cause. I'll show that in a reply to this post.

The technique is that you need to remove the back off the MEFI (carefully). Then you need to clean off the gel around the pin that is lost. Next solder a bridge from the pin that is lost to an adjacent unused pin. These are easy to recognize because there is no wirebond to the hybrid substrate. Use good flux and make a drop of solder on each ball quickly and carefully as it's a plastic housing. Then drop a small wire bridge and across the the two pins. Finally, you'll need to disassemble the cable connector and move the wire over to the position that replaces the corroded pin. In my case, I soldered a new wire so that both connections are hot. That way, if a different MEFI is installed later on, the engine will still run. Carefully re-glue and seal the MEFI (recommend starting the engine with the MEFI loose first) and then you're good to go for a while. In the interim, save your pennies. These are expensive and hard to find. I bought another as back up later and had it programmed.

Here's the overview:


Here's pin area in the upper right:


Here's a closeup photo of the bridge I soldered

Looks a little better farther away


Next post will discuss the cable problem that caused this mess.

04-27-2014, 09:59 PM
These are always good.. I have MEFI 1 - and have a spare!

Table Rocker
04-27-2014, 10:02 PM
Wow, impressive work. Glad you found your solution.

04-27-2014, 10:20 PM
Ok, so I obtained new connector hardware. This was so I could replace the corroded pins and add the extra pin to my current connector. I obtained the connector HW and a backup MEFI from the same place but I'll need to ask the MODs if I can post the name of the company.
Anyway, I received the new cable connectors and noticed that they came with a bunch funny blue plastic plugs. These were not present in my cable connectors on my boat so I was puzzled as to their purpose. And then the light comes on .... There are a number of modifications to protect the MEFI or relocate it to a dryer point. On my boat it's located right under the junction of the sun platform and the back seat so water can drop right in. However, this connector design has been used for a long time in the automotive industry. I had several underneath my Yukon for years and they didn't get wet. If you don't build it correctly it won't work. The plugs are essential pieces to sealing any unused pin locations. On the MEFI units only about 1/2 of the locations are used. These unused locations will provide a direct channel to the pin area of the MEFI if not plugged.

Here's a shot of the pieces of the connector.


Here's a shot of the "fix" that was done years ago to "protect" the MEFI. The fix is the plastic cover installed and the MEFI is below. I'm sure it helped a bit, but not much.


Here's a shot of my connector on the boat (No plugs !). What you have in this case is a direct channel to the pin area of the MEFI unit.


So, these plugs aren't too hard to take apart, but I just pushed the plugs through from the outside. The correct way is to disassemble the plug and put them in between the outer shell and the cable guide. That make a completely water tight connection. However, this works well and I checked after about 50 hours and the connection is dry.

Here's my "plugged" connector. Anyway, my suggestion to anyone who owns boats circa 1999 is to pull apart the MEFI connector and make sure the plugs are installed. If not, get some. These are key to the design of the connector.


Hope this helps someone. This connector design does work and is completely waterproof when CORRECTLY assembled.