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.
motor runs for one minute and then stops
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Originally posted by seattlesailor View PostThe 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.
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.Jeff
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S/V Bunny Planet
1971 Bristol 29 #169
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Originally posted by BunnyPlanet169 View PostRespectfully, 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+ !
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Originally posted by seattlesailor View PostFuse 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.
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
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Originally posted by JOHN COOKSON View PostThe 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
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....Jeff
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S/V Bunny Planet
1971 Bristol 29 #169
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Originally posted by BunnyPlanet169 View Post.
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....
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
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Originally posted by BunnyPlanet169 View PostAhhh! 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....
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Great, this again??
Originally posted by hanleyclifford View PostUndoubtedly 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.
Remember, 3% max voltage drop. Anything more is indeed sloppy, poor and substandard engineering/installation.
Originally posted by hanleyclifford View PostClearly the 5 amp fuse is not adequate for your installation.Last edited by ndutton; 07-05-2016, 06:24 PM.Neil
1977 Catalina 30
San Pedro, California
prior boats 1987 Westsail 32, 1970 Catalina 22
Had my hands in a few others
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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
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Originally posted by ndutton View PostA 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.
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Originally posted by hanleyclifford View PostThe 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?)
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.Jeff
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S/V Bunny Planet
1971 Bristol 29 #169
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Originally posted by BunnyPlanet169 View PostHanley - 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.Last edited by hanleyclifford; 07-06-2016, 04:37 PM.
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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.Neil
1977 Catalina 30
San Pedro, California
prior boats 1987 Westsail 32, 1970 Catalina 22
Had my hands in a few others
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