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A motor that has no battery but runs off an ECU is actually one of the more complex circuits to design. When you have a battery, it typically acts as a huge capacitor, smoothing out the voltage to all the devices that use DC power. Without a battery, you no longer have the benefit of a low impedance, slow changing ground ensured by that battery. If the impedance of that ground changes quickly (as in a poor mechanical connection anywhere in the ground circuit or a corroded connection on the ground - both incredibly common on sport vessels), you can get what's called a load dump: one of the most difficult-to-design scenarios in electronics. It is a more complex variation of the kickback I described that is inevitable with all DC motors/solenoids: it is a system-wide immediate inductance change that results in very large voltage spikes throughout your DC supply system (which runs your ECU - and can kill the devices on your ECU).

To prevent possible load dumps, the preventive fix is the exact same fix I have documented many times here on ifish. Install a central grounding bus bar. Make sure all your negative wires connect to that grounding bus bar. And then connect one fairly large (say 10 awg) wire from that bus bar to a weather -protected connection to your hull above the water line that will not corrode: typically somewhere high in your splashwell. The bus bar ensures that all your currents will sum to zero (Kirchoffs law) and that the potential at the bus bar can be connected to your hull to ensure you will have zero electrolysis on your hull. In your case, with no battery, that hull connection is the closest thing you have to a low impedance 'protective earth' to help prevent current flow in the event of a load dump.

So this goes back to my earlier post: you very likely have something wrong in your ground wiring. And the diode that is supposed to stop your fuel pump DC motor from creating a large voltage spike is either non-existent, bad, or you have a poor connection right between the diode and the ECU that is preventing the diode from doing its job. Lots of technical blather here that comes down to a simple rule of thumb: almost all weird/intermittent electrical behavior on a vessel comes down to some kind of ground problem. And a central ground bus bar with all negative wires connected to it - and the hull connected to the bus bar at one spot will fix your problems. As soon as you vary from this prescription of using one central negative bus bar, the electronics get very complex: jumbled ground wiring is a problem waiting to happen.
 

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How are these new portables with battery less efi getting away without running a dedicated ground?
Had my new efi yammie f25 that was clamped on, never had any issues. It had electric start that I used half the time, battery was not bussed to the hull, it was a floating ground.

My current motor is bolted and is grounded via the bolt to transom, but I do run all the grounds to the battery still and just recently ran a dedicated ground from batt to hull from there. This eliminated noise from my trolling motor too.
 

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There is grounding on your boat (wiring that has current flow) and bonding on your boat (wiring that ensures various parts of your boat are at the same potential - to prevent electrolysis). When you install a central grounding bus bar, you don't have to understand the difference: the grounding and the bonding will all work great if they are all connected to that central bus bar. With a single bus bar, all grounding and all bonding can occur at the same location: as soon as you start connecting your ground wires willy-nilly thinking 'it's all the same', you may or may not have created a formula for electrolysis. Every metallic system on your boat should get individually bonded to that central grounding bus bar: this ensures every item (the motor, the hull, downriggers, and any other metal in contact with the water) is at the same potential - which ensures your zincs(anodes) are at the slightly different potential (due to galvanic action) that makes sure your zincs bear all the brunt of the electrolysis and not some other metallic object (like your hull) on the boat.

So yes you can run a floating ground system with the battery-less efi motors. They work fine on glass outboard boats (assuming no downriggers and no electric trolling motor). But with an aluminum hull, you need to make sure the hull and motor are bonded with wiring (NOT the fasteners holding the motor to the transom - that frequently is a very poor electrical bonding connection) to make sure your hull and motor are at the exact same potential - and therefore your hull does not suffer from electrolysis. Keep in mind that ABYC rules require there be no more than two wires on any fastener so piling up your grounds at the battery connections almost always breaks that rule: the central ground bus bar is ideal for numerous reasons (grounding, bonding, maintaining the no-more-than-two-wires-per-fastener rule).
 

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I'm in fresh water here, do I still need to worry about electrolysis? My experience has always been with diss similar metals, so this is new.
I'll be looking for a buss bar this month.
 

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Electrolysis is usually not a problem in fresh water unless you moor your boat near other boats. Since moorages frequently provide shore power, there is a high probability you may end up mooring near an improperly wired nearby boat that is making the marina 'hot'. When you moor a boat, it is especially important to know your own boat is properly wired in order to minimize the damage caused by the nearby 'hot' boats.
 

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I agree you need a new shop. You can easily troubleshoot the fuel injectors and the high pressure fuel pump and know if they are bad before replacing them. I think you've been getting ripped off. You shouldn't have to pay for the parts if they didn't fix the problem.
 

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Hello, I had to be towed today. Found my high pressure fuel pump not operating, on my 2014 25Hp EFI. Troubleshooting myself, I found over 14volts going to a new fuel pump, but yet it doesn’t operate. If I supply battery voltage directly to the pump connector it pumps. Verified all wiring to be good. Then I thought, maybe we have a bad ground. So, I connected the connector back to the pump, but I added a wire on the ground side of the pump to the motor. Pump and motor works great. Not sure why Mercury would run it’s grounds back to the ECU, instead of grounding it’s components the the engine ground. Let me know if you think this is a legit repair? I really don’t want to go through the same problems other have gone through, and who knows maybe this fix will help others.
 

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For something that touches fuel, I would not engineer a new ground. Use it as designed and find the open in your ground circuit.

Sent from my SM-G781U using Tapatalk
 

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Pump and motor works great. Not sure why Mercury would run it’s grounds back to the ECU, instead of grounding it’s components the the engine ground.
This is ABSOLUTELY the wrong thing to do as a permanent 'fix'. What you did is a great troubleshooting approach and now tells you that you have something wrong in your ground circuit/wiring (as Joeer77 said) - which you now need to chase down. That ground NEEDS to come from the ECU so the pump current flows from the same source as the 'power' side of the fuel pump circuit in order to prevent any ground loops. As soon as you introduce ground loops, you will likely get very strange behavior and intermittent failures throughout your boat.

Grounding is one of the least understood subjects in electrical engineering: I have had long discussions with fellow electrical engineers on this subject and even they don't fully comprehend it. Very easy to get wrong advice and you will assuredly get wrong advice about grounding over the Internet since it requires a keen understanding of current flow, isolation, transmission lines and transients.

I have repeatedly advised everyone here to have just one ground bar on their vessel and run all of their ground wires to that single ground bar - because otherwise it requires a very good understanding of grounding and bonding to take any other approach. When I go aboard sport vessels to troubleshoot, I find improper grounding on close to 99% of vessels. And improper grounding is the source of the vast majority of electrical problems. People on the Internet will have strong opinions and will incorrectly cite references not realizing the subtleties.

In your case, I would rewire my boat to ensure there is only one ground bar and ALL grounds/bonds go to that single ground bar. All engine grounds should also go ONLY to that common ground bar (not daisy chained to battery negative terminals). And chase down the discontinuity on the fuel pump ground to your ECU. The proper way to fix this is to wire your boat correctly using that one ground bar, then determine if your ECU fuel pump ground is still open. People tend to ignore this advice since it is a lot of work to properly wire your boat - and convince themselves that it is OK to have a rats nest of ground connections since it is 'just ground'.
 
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Using ground for component trigger is quiet common. Looked over the service manuals I have, the ECU not triggering or closing circuit for pump is odd. It needs to see a crank signal from hall sensor on flywheel to know that motor is turning. This will trigger the pump, injectors and opens the circuit on coils to fire. The only other item that will trigger a fuel shut off is the lanyard kill switch if that circuit closes to ground.

For fuel operations it uses crank position sensor, oil pressure switch, engine coolant sensor and overall battery voltage. Only one of those will trigger fuel cutoff which is cps.
Manual also says disconnecting any of the above sensors will not stop the motor, except the crank position sensor. This is the one sensor if it fails, motor will not run. Other sensors indicating a failure or out of range reading will put motor in limp mode.

Do you have a tach in the boat? Cranking motor do you see the tach moving?
Crank sensor resistance is 300-350ohms
Did the flywheel jump or break the keyway, hey it is an item per manual to check.
Have you checked the kill lanyard connections? If that circuit is closed to ground it will also kill motor. This one is easy disconnect the lines will open that circuit, it could be as simple as the cutoff switch is bad too.
 

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I
This is ABSOLUTELY the wrong thing to do as a permanent 'fix'. What you did is a great troubleshooting approach and now tells you that you have something wrong in your ground circuit/wiring (as Joeer77 said) - which you now need to chase down. That ground NEEDS to come from the ECU so the pump current flows from the same source as the 'power' side of the fuel pump circuit in order to prevent any ground loops. As soon as you introduce ground loops, you will likely get very strange behavior and intermittent failures throughout your boat.

Grounding is one of the least understood subjects in electrical engineering: I have had long discussions with fellow electrical engineers on this subject and even they don't fully comprehend it. Very easy to get wrong advice and you will assuredly get wrong advice about grounding over the Internet since it requires a keen understanding of current flow, isolation, transmission lines and transients.

I have repeatedly advised everyone here to have just one ground bar on their vessel and run all of their ground wires to that single ground bar - because otherwise it requires a very good understanding of grounding and bonding to take any other approach. When I go aboard sport vessels to troubleshoot, I find improper grounding on close to 99% of vessels. And improper grounding is the source of the vast majority of electrical problems. People on the Internet will have strong opinions and will incorrectly cite references not realizing the subtleties.

In your case, I would rewire my boat to ensure there is only one ground bar and ALL grounds/bonds go to that single ground bar. All engine grounds should also go ONLY to that common ground bar (not daisy chained to battery negative terminals). And chase down the discontinuity on the fuel pump ground to your ECU. The proper way to fix this is to wire your boat correctly using that one ground bar, then determine if your ECU fuel pump ground is still open. People tend to ignore this advice since it is a lot of work to properly wire your boat - and convince themselves that it is OK to have a rats nest of ground connections since it is 'just ground'.
I've been following this thread trying to grasp the ground bar importance. My old fiberglass boat has a few rats nest grounding issues and some rather creative wiring for accessories. How does this work with a Glass hull vs an aluminum? I have duel batteries with an I/O and a kicker with electric start. (No EFI) . But would love to rewire this with a single grounding bar and clean up some messes.

Question: Do you run a ground wire from the engine block to this new ground bar ? or do you need a line to the outdrive itself for water bonding. Thanks, Kirk
 

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The beauty of a single ground bar is that you don't have to understand the difference between grounding and bonding. Just run everything that needs to be grounded or bonded to that bar - and it just works. If you are not sure what to do: run your wire to that single ground/bonding bar and you are golden. On a glass hull, you'll want to make sure you've bonded everything in contact with the water: run a wire from the I/O to the ground bar, run a wire from the engine to the bonding bar, run wires from each battery negative to the bonding bar, run your downrigger grounds to the bonding bar and so forth. It just makes things easy. Yeah it is a lot of wire but you will get a very reliable boat and a boat where electrolysis is minimized.
 

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Ben, Did this ever get solved?
 
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