evinrude 100 electrical issue

[fishdog4449]

got the motor for free from a friend,said it ran, but a diode(thats what he called it, not really sure what it is) in the control box gets hot and starts smoking. not good. I didn't try to start it, but oiled the cylinders and tried to turn it over. it turns over slowly and the starter gets stuck occasionally. the diode does indeed get very hot very quickly as do the battery cables. Here is the pic of the diode, I was thinking I should replace battery cables first then inspect all wires for shorts or stripped insulation. any other ideas guys! Thanks!
Also, what should compression be for these crossflows? I'm gettin 90psi exactly on all four.

 

[HighTrim]

Re: evinrude 100 electrical issue

You did not mention a year or model number?

If your compression results are within 10 percent of one another, all is well.

The heat in the wiring is from resistance. As you said, look for cuts, nicks, abrasions, or crunching when you flex it. Also polish all connections and re tighten. Make them shine!

 

[F_R]

Re: evinrude 100 electrical issue

That diode is called a "blocking diode". It's a long story, but it's in the shift circuit. It prevents the shift circuit from feeding the ignition circuit. If that happens, you can't turn the motor off. It obviously is burned up and needs a new one. Offhand, I don't know why it burned up, so check things out before putting a new one in to burn up also. Something is screwed up for sure. Is the battery installed with correct polarity?

 

[fishdog4449]

Re: evinrude 100 electrical issue

Sorry bout that its a '72 Evinrude 100hp 90degree v4
The diode is connected on one end to the key switch so that makes sense. I have a second set of controls which does the exact same thing. Neither diode is burned out, as soon as it got hot I disconnected battery. The batt was connected right way. In FWD, diode doesn't get hot. Crank it and shift to neutral and in about 2 seconds it starts to heat up. The motor shifts just fine though.
Is there anyway I can test the solenoids with a meter (by wires going into lower unit) to see if they are alright?

 

[fishdog4449]

Re: evinrude 100 electrical issue

Figured out the slow cranking problem, replaced battery cables and it cranks very fast. Decided to run it in FWD to make sure it ran well before I spent to much time working ont he diode problem. started from cold in 2 seconds and ran perfectly. water pump needs repaired but pumped enough to run it for a few minutes on the stand. ran a can of seafoam through and compression came up to 105 on all four, up from 90. the motor shifts fine and runs fine in all gears, but in reverse and neutral the wire leading from ignition to diode heats up. I'm sure if I left in running in neutral for a while the diode would heat up to, but the wire heats first. I inspected every inch of wiring and all the wires look great. they are all in perfect shape and most ignition components look brand new.

it appears as though a repair was performed on LU because VERY new wires lead down to LU and are spliced to the green/blue shift wires.

looks like it has a brand new switchbox, starter solenoid, coil, plug wires, and internal harness.

but the problem remains, any ideas??

 

[F_R]

Re: evinrude 100 electrical issue

There is something screwy going on there. It sounds like you have a short to ground in one or both of the blue/green wires. It is drawing too much current. The resistance of the solenoids should be 5-6 ohms. But you say it shifts OK, so it isn't the solenoids. I am very suspicious of those patched wires!!

The blocking diode normally will get warm when in neutral or reverse, but not hot hot. Yours looks like it is getting hot hot since it burned or melted the epoxy off it.

Also, the shift is fed by another circuit when running. It is fed by the alternator as well as the key switch feed. That takes much of the load (and heat) off the blocking diode. So, that brings up another question: Is your alternator working?

But even so, it should not be melting the blocking diode. Otherwise they would all melt down everytime somebody left the key turned on when not running.

EDIT: My prediction: Those wires going down to the lower unit are not inslulated well enough. They go through water on their way down there. Electrical current is leaking off through the water to the housing, a partial short circuit and cause of excessive current draw in the shift circuit.

Prediction #2: On top of that, your alternator probably isn't working. But that remains to be confirmed.

Now to rest my brain after thinking about this so hard.

 

[fishdog4449]

Re: evinrude 100 electrical issue

Wow thanks F_R!
You guys are great.
The covering didn't melt what happened was the previous owner cut the insulation off the diode in order to see it to determine what it was. Actually, I have only ran the engine in Neutral and Reverse long enough until the diode gets warm because I didn't want to ruin any other components; the PO told me that the diode actually started smoking when he ran it.
I have the manual now, so I will run an alternator test tomorrow as well as let it run longer in N and see if the diode gets hotter.

When I pull the LU to replace the impeller, I will double check the wires, but they look brand new going down into the LU from the powerhead so I'm not sure.

EDIT: When I re-watched the video of the engine running, I noticed that RPM dropped when I briefly shifted into reverse. Not sure if that has anything to do with the possible alternator problem or not, just puttin it out there.

 

[F_R]

Re: evinrude 100 electrical issue

Reverse gear puts a bit more load on the hydraulic pump that does the shifting. Most people aren't sharp enough to notice the difference.