motor runs for one minute and then stops

[seattlesailor]

Fuse is off the coil like on Moyer's marine wiring schematic. The only difference with the schematic is that the existing wiring we replaced had a two prong connector at the OPSS, one going to the starter and one going to the pump. Once the fuse was blown we could still run the motor for a minute with the starter as mentioned in my initial post.

[seattlesailor]

The fuse I installed is the 5 amps fuse from the kit not 10 amps.

[BunnyPlanet169]

The only difference with the schematic is that the existing wiring we replaced had a two prong connector at the OPSS, one going to the starter and one going to the pump.

Hmmm. 'Going to the starter'? I don't understand this.

The fuel pump circuit should only be Coil + --> Fuse --> OPSS --> Fuel Pump.

It there is another power take off from the OPSS AFTER the fuse, that's what's suspect.

[hanleyclifford]

Respectfully, I disagree. IMO, it is perfectly good engineering in having a large, protected wire to coil +, and then short branch circuits from there.

There are a several loads in close physical proximity to coil + that are only normally energized from IGN on the starter key switch. Coil, E.I., fuel pump, alternator excite.

I actually installed a small terminal block next to my coil yesterday for exactly this reason. Too many terminals to hang off the coil+ !

Undoubtedly you can get away with that but you should know the potential for voltage variations is greater than if you had separate circuits. The question then becomes: what is the problem with voltage variations at coil +?

[JOHN COOKSON]

Fuse is off the coil like on Moyer's marine wiring schematic. The only difference with the schematic is that the existing wiring we replaced had a two prong connector at the OPSS, one going to the starter and one going to the pump. Once the fuse was blown we could still run the motor for a minute with the starter as mentioned in my initial post.

Bet I know what the problem is!
The wire going to the starter is worn and rubbing against the engine block somewhere. This is where the short to ground is. Let the wire loose at the starter solenoid and pull it around the engine and inspect it. I've been through this exact drill. Kept me guessing for awhile.
The wire from the starter that is co joined with the lead to the fuel pump bypasses the OPSS so the fuel pump operates while the engine is being cranked.

TRUE GRIT

[BunnyPlanet169]

The wire from the starter that is co joined with the lead to the fuel pump bypasses the OPSS so the fuel pump operates while the engine is being cranked. TRUE GRIT

Ahhh! I get it, thanks. I bet you're correct.

Is this really necessary? I would have thought there was enough fuel in the carb bowl to start, and oil pressure builds quickly while cranking anyway....

[JOHN COOKSON]

.
Is this really necessary? I would have thought there was enough fuel in the carb bowl to start, and oil pressure builds quickly while cranking anyway....

No, the bypass wire to the fuel pump wire from the starter is probably not necessary for the reason you mentioned.
This wire is shown in the wiring diagram for a late model engine with an electric fuel pump so it was a standard feature back then. I don't have a scan of the wiring diagram on this computer so I can't post it. I have the original A4 owner's manual so I know it's there. Perhaps there is a scan of it in the Drawings and Schematic section.

TRUE GRIT

[hanleyclifford]

Ahhh! I get it, thanks. I bet you're correct.

Is this really necessary? I would have thought there was enough fuel in the carb bowl to start, and oil pressure builds quickly while cranking anyway....

In 25 years of running these engines up and down the coast I have had only one instance where the normal cranking was not able to develop enough oil pressure to engage the OPSS (s) for ignition and electric fuel pump. This occurred after 10 hours of hard running north on the Chesapeake, head wind just as I entered the basin at Chesapeake city. I coasted to the anchorage and the engine started after ten minutes. I do not recommend putting the fuel pump on the "R" terminal for the same reason I recommend keeping the sea valve closed until the engine is running.

[ndutton]

Great, this again??

Undoubtedly you can get away with that but you should know the potential for voltage variations is greater than if you had separate circuits. The question then becomes: what is the problem with voltage variations at coil +? . . . . . . IMO mixing ignition, pump, alternator on the same circuit is sloppy engineering.

A properly engineered circuit tolerates all connected loads regardless of their sum with no more than a 3% voltage drop. If you're experiencing more than 3% you need to re-read and understand the many posts on this forum describing voltage drop in detail, then rewire the substandard circuit according to established protocol. Alternatively, if you're unwilling to wire the circuit properly you can certainly add more and more circuits. A properly sized single circuit is far less complicated than several circuits with several oil pressure switches and much easier to troubleshoot due to its simplicity.

Remember, 3% max voltage drop. Anything more is indeed sloppy, poor and substandard engineering/installation.

Clearly the 5 amp fuse is not adequate for your installation.

Sure it is and the fuse is doing exactly what it's supposed to do. Moyer Marine has sized the fuse in their kit @5 amps for good reason. The best any of us can do is follow the instructions included in the kit.

[seattlesailor]

Thank you all for all your contribution. I grabbed the A4 electrical schematic from Jeff response above (http://www.moyermarine.com/forums/sh...ring+schematic) and have a good idea of what I will do next. All your input is extremely valuable.

Michel

[hanleyclifford]

A properly engineered circuit tolerates all connected loads regardless of their sum with no more than a 3% voltage drop. If you're experiencing more than 3% you need to re-read and understand the many posts on this forum describing voltage drop in detail, then rewire the substandard circuit according to established protocol. Alternatively, if you're unwilling to wire the circuit properly you can certainly add more and more circuits. A properly sized single circuit is far less complicated than several circuits with several oil pressure switches and much easier to troubleshoot due to its simplicity.

Remember, 3% max voltage drop. Anything more is indeed sloppy, poor and substandard engineering/installation.

Sure it is and the fuse is doing exactly what it's supposed to do. Moyer Marine has sized the fuse in their kit @5 amps for good reason. The best any of us can do is follow the instructions included in the kit.

The 3% voltage drop mantra is arbitrary and violated everywhere with impunity. Read the source of it and you'll see why. Sizing of fuses should be based on actual load, not a recommendation, and we have seen what can come of studious attention to manufacturer's propaganda. (remember Pertronix?)

[BunnyPlanet169]

The 3% voltage drop mantra is arbitrary and violated everywhere with impunity. Read the source of it and you'll see why. Sizing of fuses should be based on actual load, not a recommendation, and we have seen what can come of studious attention to manufacturer's propaganda. (remember Pertronix?)

Hanley - I really don't understand where you're going here. Are you dissing the NEC and ABYC? These are well intentioned, and well supported fire safety codes.

3% is an excellent design goal, and inherent in that calculation is the circuit design current, ampacity of the wire, the temperature of the space, and ultimately the fuse requirements.

Numbers greater than 3% will work, no doubt for a while, but the risk is a runaway thermal reaction - as voltage drops, the current goes up, heating the wire, which increases it's resistance, which further drops the voltage, which increases current, which eventually burns the insulation and shorts.

I've burnt up extension cords doing just this.

I don't know why you'd want to recommend ignoring this.

[hanleyclifford]

Hanley - I really don't understand where you're going here. Are you dissing the NEC and ABYC? These are well intentioned, and well supported fire safety codes.

3% is an excellent design goal, and inherent in that calculation is the circuit design current, ampacity of the wire, the temperature of the space, and ultimately the fuse requirements.

Numbers greater than 3% will work, no doubt for a while, but the risk is a runaway thermal reaction - as voltage drops, the current goes up, heating the wire, which increases it's resistance, which further drops the voltage, which increases current, which eventually burns the insulation and shorts.

I've burnt up extension cords doing just this.

I don't know why you'd want to recommend ignoring this.

I do not recommend ignoring anything useful. However, of far greater importance than arbitrary goals is the design and propagation of an electrical system, "tree" if you will. The only good voltage drop is the intentional one, and we have seen here a number of unintentional voltage drops that had useful results. I follow the rule that no wire should be larger than the wire that feeds it. You would be surprised at how many violations of this occur. Similarly, no wire should feed more than one wire equal to itself, or any combination greater than itself. This is one reason why coil + should remain as clean as possible. There is a lot more to building a clean, safe and effective system than rigid adherence to arbitrary numbers. If voltage drop is a big priority (as it should be), here is a practical suggestion: start the system with the largest wire practicable for present and any future considerations. For me that means #2 cable coming off the batteries, both red and black, and ganging them up to a big buss bar before distribution.....maybe we should start a thread on DC system construction?

[ndutton]

Just when I thought I'd heard it all

Wow Hanley, just Wow.

Jeff, I admire you for trying to offer reason but you'll find the other side of the argument is belief based rather than proven physics and electrical engineering/design as set forth by the ABYC, NFPA and NEC and is not interested in anything those safety agencies have to say. Previously the belief based side has even advocated the ABYC is outdated and should be rewritten to align with the beliefs (don't hold yer breath waiting for that to happen).

Anyway, thanks for trying.

[seattlesailor]

I ran the motor fro many hours on a recent trip and the motor never stopped and ran very reliably.
Changing the pump with the moyer's kit and changing the fuel hoses was the right thing to do.