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Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 16097
Experience:  Degree in Marine Technology. Gas and diesel marine mechanic.
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My 90hp etec keeps blowing engine fuse. I believe the problem

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My 90hp etec keeps blowing engine fuse. I believe the problem started when I attempted to start without any fuel. After suppling fuel the problem still existed. I checked the earth cable from the battery to the ignition switch and the copper wires are black at the battery but copper at the ignition switch. I have bled the air out of the fuel system but the problem exists.
Hello, my name is XXXXX XXXXX I will be helping you today. I have a question back to you. If you turn the key just to run, and not start, does the fuse blow then? Or does it only blow when you turn the key to start?
Customer: replied 4 years ago.

The fuse blows when ignition is in on position

Gotcha Dave. Step 2 is to disconnect the high pressure fuel pump. Just disconnect the pigtail to it. Pop a new fuse in and try it, let me know if the fuse still blows.

Customer: replied 4 years ago.

The motor is 400klms away. I would like some options before I make the trip. Lets say the fuse still blows.

Basically you unplug everything. If the fuse still blows the harness is shorted. If it does not blow then you start plugging things in 1 by 1. (The ECM, Harness connections ect ect) until the fuse blows. Then whatever you plugged in last in the culprit. However, it is more than likely the fuel pump causing the issue. Fuel is a coolant, and if you run the engines dry on fuel, the fuel pumps heat up and burn out. It's not different than if you have an electric hot water heater for your house. If you plug it in, and there is no water in it, the heater elements burn right out. Does that make sense?

Customer: replied 4 years ago.

Yes it does thanks. So i should source a fuel pump because initially it was winding over before the fuse blew. Is there more than one fuel pump? Thanks

There are 2 fuel pumps on the engine, but only 1 is electric. The other is mechanical and has nothing to do with the fuses. The fuel pump would be the first thing I would look at given what you said happened to the engine. Personally I would not buy a new fuel pump until I confirmed that unplugging it keeps the fuse from blowing. It's a 230 dollar pump is US dollars, and often times you can not return them. (my system tells me your from AU, and I am in the US and everything is in US dollars to me.)


That should do it. Feel free to fire away if you have any more questions on this.

Thanks in advance, and good luck!


Customer: replied 4 years ago.

Hello, After disconnecting the fuel pump the problem still exists. I have identified the fault in the ignition switch. When the rectangular plug which houses the ignition wires is connected with the key in the on position a click sound is heard within the throttle control seconds before the fuse blows. Thanks

Your very welcome Dave. Thank you and happy holidays!


Customer: replied 4 years ago.

Hello Jason, You have not answered my question. I do not wish to rate a poor response until I have to.

Customer: replied 4 years ago.
Relist: Incomplete answer.
I have not received an answer to my problem


You have me confused. You wrote "I have identified the fault in the ignition switch."

That tells me you found the problem, No??

Customer: replied 4 years ago.

Hello Jason, sorry for the confusion, I disconnected the fuel pump and the fuse still blows. A clicking sound is heard within the throttle control before the fuse blows. I did not mean to say I have identified the fault but trying to provide clues for you to help solve the problem. Where else apart from the fuel pump could cause such a problem? Only the engine controls are connected to the battery. The connections to the battery are clean and secure. I have to tow the boat 200 klms on a rough dirt road if I cannot solve the problem.

The way you wrote your previous response it was written in such a way that you inferred you narrowed down the problem to the keyswitch. Thats not the case then.


Have you disconnected the EMM yet? (the engines computer) and tried it? I wrote to do that in an earlier response of mine.

Customer: replied 4 years ago.

Yes I have and the fuse still blows


Step 1 is to replace the keyswitch to make sure that is not shorted internally. If that is not it, then there is a short in the harness. In order to keep from having to have an endless supply of fuses on hand. What the next step is, is to get a digital multimeter and set it to continuity. Stick 1 end to battery ground, disconnect the harness at the keyswitch. And see which wires are shorted to ground. Your ability to find it is going to depend on how good you are with a multimeter. This is where it tends to get over most folks heads. But feel free to reply back with further questions.


Customer: replied 4 years ago.

Hello Jason, I have tested the key switch. Continuity = Key Off: Bw/By Key On:Pu/Rb Key Start: Pu/Rb/Yr Does this help you?

Are you getting continuity between black and purple or black and red?
Customer: replied 4 years ago.

When key is in off position continuity between black/white line and black/yellow line. When in on position between purple and Red/blue line wires. When in start position between purple wire, red/blue line wire and yellow/red line wire.

When testing the harness, continuity between black/white line wire and yellow/red line wire and purple wires.Continuity between yellow/red line wire, black/white line wire, purple wire and the red wire.

Black/white is your ground. The only thing that should have continuity to is the black/yellow with the key in the off position. That would be the stop circuit. If you have contiuity between the black/white and any other wire other than the black/yellow, then keyswitch is bad.
Customer: replied 4 years ago.

That is not the case. The key switch I think is reading correct but I am not sure about the harness. The earth wire has continuity with three other wires. Where would that issue lead to?

The earth wire should not have any continuity to any other wire in the harness by itself. Next step is to disconnect the harness from the engine adn see if it still has continuity or not.
Customer: replied 4 years ago.

When I test the female side of the harness plug behind the flywheel which continues down the lhs of outboard looking from the rear the black wire has continuity with the yellow/red wire.

Is that with or without the keyswitch hooked up?
Customer: replied 4 years ago.

Without the key switch connected

Thats going to be a shorted extension harness then. The start wire (yellow/red) is grounding out. You could try slicing open the harness with a razor blade very carefully and try to find where the yellow/red and black have rubbed together. But thats if you have more time than money, as it can be real time consuming. In the shop we would just replace the harness, as you never know what else might be shorting inside of it. Usually what you find is they have rubbed through a screw someplace, like rubrail screws. But you found the monkey.

Feel free to reply back if there is anything else Dave. If not, please do not forget to re-rate me. Thanks again. --Jason

Jason and other Boat Specialists are ready to help you
Customer: replied 4 years ago.

Hello Jason, I have scanned the harness and found no place where it has rubbed through on a bolt or screw as you suggested. The motor has done 23 hours. Upon checking resistance at terminal A and terminal B of the starter solenoid which are subsequently the signal wires I found resistance of only 5 ohms which suggests a closed circuit and the cause of the direct short in the ignition system. Also the CPS resistance is out of spec. It should read 560 ohms but there is no circuit at all. What are your thoughts on these findings. Thanks

Dave. I thought you had the harness disconnected from the engine side this whole time. Did you not?
Customer: replied 4 years ago.

Upon checking resistance at terminal A and terminal B of the starter solenoid which are subsequently the signal wires I found resistance of only 5 ohms which suggests a closed circuit and the cause of the direct short in the ignition system

Are you talking about the 2 small posts on the solenoid?
Customer: replied 4 years ago.

No. The two posts are battery positive and starter positive. there is a plug below and between these which houses yellow/green wire terminal A (neg) and yellow/red wire terminal B (pos). I would not think I should be getting a reading of 5 ohms between these terminals.

Thats the actual wires for the electromagnetic coil inside of the starter solenoid. That will read low resistance.
Customer: replied 4 years ago.

The CPS sensor resistance reading is at least 4000ohms. The spec is 500 ohms. Could that fault cause a direct short when ignition is turned on?


No. The CPS may very well be bad, but that is not the issue. That is why we started in the beginning by disconnecting the ECM. That rules out the ECM and all of its sensors.
Customer: replied 4 years ago.

Could the neutral start switch in the throttle control which can only be checked from inside develop a short and cause this problem. It is the only switch I have not checked.

Dave. I had asked in the beginning here if the fuse blows when you turn the key to "Run", or if you turn the key to "start". You said "run". Is that still correct?
Customer: replied 4 years ago.

Yes the fuse blows when in the on position. There is no continuity between starter solenoid terminal B (yellow/green) wire and yellow /red wire at either neutral start switch and pin 32 at J!-A plug. On visual inspection the wires are not touching in the encapsuled resin type substance at the junction of these wires. There is a gap of 50mm between the wires. How did I manage to clock up 20 hours of motor use with this condition present?

If its popping the fuse with the key in the run position it has nothing to do with the yellow/red wire, as that is the start wire.


With everything hooked up except for the battery, and a good fuse in place, and the key in the run position. What is the resistance to engine ground on the purple wire?

Customer: replied 4 years ago.

Is that everything hooked up or J2 disconnected so access to purple wire is possible. If everything is hooked up how do I access the purple wire?

You can grab it at the keyswitch, up front.
Customer: replied 4 years ago.

Resistance between purple and ground is 134 ohms

Customer: replied 4 years ago.
Relist: Incomplete answer.
When the ignition is in run position and the resistance between the purple wire and ground is 134 ohms. What is the status of the ignition switch?
Customer: replied 4 years ago.

134 ohms

Customer: replied 4 years ago.
Relist: Other.
been waiting hours for an answer
Sorry for the delay Dave. We do this on the side, out of our houses. You are in AU, I am in Florida, USA. And we are probably 15 hours apart time zone wise. As I write this, it is probably middle of the night for you. At this point I would bring it in to the dealer to see if the the EMM is fried, or if there is a problem with the capacitor on the engine. We have gone as far as we can go with this one online. And it needs some hands on attention.
Customer: replied 4 years ago.

Hello Jason, the problem with my fuse blowing was when the engine was installed the purple wire was allowed to be hard up against the the ground post of the trim/tilt gauge. I used the motor for one trip travelling 120 nautical miles. The motor then sat for some months and the insulated lug managed to make contact with the ground post causing the overload. I am fortunate the problem began while on land and not at sea as I was out of radio contact at the most distant part of my trip. I falsely thought it was linked to attempting to start the engine without any fuel. I managed to obtain the manual online and now have a far greater understanding of component locations and tests required to test such components. I want to thank you for your efforts to help me solve the problem and are happy to rate your answers more than ok. Regards Dave

Hi Dave,

Thanks for the follow up. I knew it was in that purple wire someplace. If you scroll up and re-read our conversation starting from 11/29 forward I was having you test for continuity between purple and black. It looks like it was there and you just missed it the first time around.

Either way, I'm glad to hear you are up and running. And you are right, much better for it to happen now vs when your 20 miles offshore!



Customer: replied 4 years ago.

Hello Jason, When tested for continuity between purple and black there was no continuity. I am of the belief that sometimes continuity tests are not always effective. Is it not possible for no circuit to exist at rest but when voltage is applied there is enough power to overcome the delicate resistance that exists?


I see what your saying, but no not really. The way a continuity tests works is the actual meter applies voltage to a wires, and then it looks for that voltage on the other. lead. Resistance tests work the same way. Every brand of meter uses different voltages. But for example. I use fluke meters. And when doing a resistance or continuity test the way it works is the meter sends out about 8v on the negative meter lead, the positive meter lead then looks for that 8v. If the meter see's the full 8v, it knows there is full continuity with very little resistance int the circuit. Resitance causes drops in voltage. So if the meter see's less than 8v, it can convert what it sees into ohms, and give you a reading in ohms.
Customer: replied 4 years ago.

Hello Jason, I wish to close the question. I have already rated the answer as excellent. If I rate you again it is asking for the amount I have already paid. Dave