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What would cause voltage fluctuation throughout my 86 Ski Eliminator?

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Eliminator

I have a 1986 Ski Eliminator that I've been restoring. New engine, carb, MSD EI, starter, coil, solenoid, oil pressure sending unit, temp sending unit... you get the picture. The boat starts right up and idles great. However, none of the gauges, tach, lights, or bilge pump were working. I quickly discovered that the ground wire from the engine to the dash was totally melted and grounding to several of the + wires under the dash. I believe this is because the wiring harness was coiled up in the bilge, with a splice going to the bilge pump. I think it got wet. Anyway I replaced all the ground wires throughout and the red + wires to the guages, and blue + to the lights. All other wires seem to be intact. Now with the boat running I have working temp gauge, fuel gauge, batt gauge, lights, bilge, and blower. Unfortunately my oil pressure (New sending unit) pegs out, and my tach doesn't work at all. I have tried wiring the tach signal wire to the designated output on the msd ignition module ( voltage here fluctuates between 4.5v and 2v can that be right?) and I also tried connecting it to the - side of the coil. Still nothing. Ive also tried bypassing both the + wires and grounds directly to the battery on both guages. Still no joy. When the engine is not running all the positive leads everywhere match the voltage from the battery. But when it's running the voltage fluctuates between 12.5v to 9v through the system. Even at the battery. Could this be the alternator? I hate to go buy a new one without some helpful advise. If anyone can help me I would really appreciate it!

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Woodski

@Eliminator:  Alternator question - I would find a local starter repair shop, they should be able to test your alternator for output.  Could be the regulator.  When it drops low, are you running some ancillaries (blower / stereo?).   Tach issue - have you connected a different tachometer to it, or a test tach which you may be able to borrow / rent from a local auto parts store if you don't have one.  The MSD website may have some troubleshooting guides on output signals.

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Eliminator

Thanks Woodski. I ran around today to a few places in town but nobody has a way to test it because its marine i guess. I did get some input from a guy at napa who mentioned the voltage regulator as well. When i turn the ignition to "on" i lose 1v at the auxiliaries, but maintain 12.4v at the battery. Thats with everything off. Then when i start it the voltage jumps pretty actively from 0.5v to 14.5v, everywhere from the battery to the bow light. Im amazed its running at all. Ive checked and rechecked all grounds, and can't find anything lose. The voltage regulator built into the alternator is the only thing left I can think of. Also I did use a test tach last night and have the same results... no tach. 

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braindamage

Call msd tech support about the tach. I have an old Jeep that required a conversion module for my stock to work.

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Woodski

With the engine running, 2 items - could the vibration be causing a short / open on one of the circuits and/or now that the alternator is spinning it is doing that very thing.  Maybe a good car dealership or classic car restoration place would have a test bench.

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Eliminator

Braindamage: I think you might be right about calling MSD, as the rpm signal comes from the ignition module. 

Not sure if that will help the voltage or not.

Woodski: Rather than calling around wasting time, or driving around wasting gas... (I kinda live in the boonies). I ordered a 105v three wirr alternator from DB Electrical for just $55 last night. If it doesn't do the trick then I have a spare... never hurts to have spare parts. I getting a good collection.

But I just thought of something guys. I just recently installed a new solenoid as the old one stuck while bridged. The new one grounds to the mounting bracket whereas the the old one do not. In other words the are a tad dissimilar. Do you guys think that might cause a voltage flux?

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braindamage
6 hours ago, Eliminator said:

Braindamage: I think you might be right about calling MSD, as the rpm signal comes from the ignition module. 

Not sure if that will help the voltage or not.

Woodski: Rather than calling around wasting time, or driving around wasting gas... (I kinda live in the boonies). I ordered a 105v three wirr alternator from DB Electrical for just $55 last night. If it doesn't do the trick then I have a spare... never hurts to have spare parts. I getting a good collection.

But I just thought of something guys. I just recently installed a new solenoid as the old one stuck while bridged. The new one grounds to the mounting bracket whereas the the old one do not. In other words the are a tad dissimilar. Do you guys think that might cause a voltage flux?

Yep. I was just commenting on the tach about calling msd. That’ll have nothing to do with the voltage drop.

I doubt the new solenoid is the source, but maybe. I would think this would show up as not engaging the starter.

i think you have a bad or intermittent ground , or you have a bad voltage regulator. I hope it’s the latter cuz the former is a major PITA. Trust me, I have an old Jeep and tracing down the source of grounding issues will drive you to drink!  

I’m not sure, but does a ‘bu have a floating ground?

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Eliminator

Yeah I wasn't too optimistic about the solenoid either I just know it wasn't the same as the other one. 

I've gone over the entire boat checking every ground I can find. Searched for warm wires or accessories. Rewired about 40' of new wires. I was able to get several things working that weren't before... lights, fuel gauge, temp gauge, voltage meter, bilge pump, even the clock. Now I'm just missing the tach input, and the oil pressure gauge pegs as soon as I start the engine. I have that new alternator on the way too. So I guess we will see if it's the voltage regulator. That seems to be pretty much a unanimous opinion. Along with ground issues. It's such a beautiful boat, and I'm so close to having it 100% again. Thank you for helping me figure this thing out!

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justgary

Disconnect the alternator electrical connections completely and then run the engine to see if it is causing your voltage problems.  I bet it's ok.

I think you have a loose wire in the Cannon plug where the boat harness meets the engine.  Disconnect the plug, clean it out, and *gently* spread the male contacts with a small blade.  I usually apply a small amount of grease at each contact before I reconnect the plug. 

Also check your main ground lug at the back of the engine, probably on one of the heads.

Is the alternator you bought a marine-rated one?  Please tell us yes....

Regards,

- Just Gary

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Eliminator

Just Gary, Thanks for your input! As a matter of fact, late last night I tried exactly that. I unplugged the alternator completely and unfortunately the voltage still fluctuates. And yes I absolutely got a marine alternator. Just another spare part I suppose. And by the way I discovered that Napa actually sound me a automotive oil sending unit! So ordered another one of those. That should fix the oil pressure gauge. So I'm just down to the tach (gonna call MSD on that), and the voltage issue. I will go over the main grounds again and apply some grease at each end like you suggest. I'm determined to figure this thing out! Thanks again...

Another Gary

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