Starting Issue - Twin 1988 Merc 4.3's

[PosessionSound26PC]

Let me first thank @San_Diego_SeaRay for the help he provided on my previous issue with my 1989 Formula 26PC - starting issues due to bad/corroded starters and slave solenoids. Previous post here:

Starting Issue After Unrelated Mech Repairs

I have a 1989 Formula 26PC w/ twin Merc 4.3 and Alpha I's. Long story short: starboard engine froze up, shop where I store boat said new motor needed, buddies and I decided to do it ourselves w/ rebuilt motor so prepped by tearing stuff off (exhaust, electrical, etc), decided to look for the...

forums.iboats.com

I finally got the boat on the water late last year for a test run and ran into two more problems. After letting the motors warm up at dock (all gauges seemed fine), we headed out in the no-wake zone while I kept an eye on the gauges. Maybe 10 minutes later, I noticed the Port motor starting to overheat and I shut it off after a while and limped back to the dock on Starboard. I can troubleshoot that on my own this winter (thermostat or failed impeller?) but while trying to winterize the motors, I ran into the following starting issue:

(I have brand new batteries and starters for both motors, and ignition wires and starter slave solenoid for starboard only)

Started starboard motor, let it warm up. It started/turned-over strong. Sounded good. I remembered I had forgotten to grab the fogging oil and shut off the motor so I could go get it. Came back and for the life of me, I could not start that motor again. It turned over strongly - no sign of battery or starter motor weakness, just no ignition...

Decided to move on to Port motor - I thought maybe the batteries HAD weakened so maybe having Port turning would let me start Starboard. Successfully started Port - again, it turned over strongly and there was no sign of weak battery.

Now here's where it gets weird for me: while Port was running, I attempted to start Starboard again. As soon as I turned the key, Port immediately died. I haven't had a chance to look at the wiring schematic yet... I know there is a 50A circuit breaker but since the Starboard starter works, I assume that isn't the problem... There's a 20A fuse somewhere at the key but again, the starter turns over so assume that isn't it... Coil?? What would engage with the key to ground out the Port motor while running? I should mention that this was repeatable - attempting to start Starboard kills Port every time.

 

[stresspoint]

i could be wrong so a guess would be a bad ground or grounds to the motors.
it would be a matter of taking them all off and cleaning them as it is very hard to speculate not being able to view your set up.
weird stuff can happen because of a single bad ground in boats.

also you may want to take a quick look at the key switch wires to check for corrosion, thinking maybe feedback /draw from one switch to the other..

 

[PosessionSound26PC]

i could be wrong so a guess would be a bad ground or grounds to the motors.
it would be a matter of taking them all off and cleaning them as it is very hard to speculate not being able to view your set up .

also you may want to take a quick look at the key switch wires to check for corrosion..

I checked all grounding when I had my starter issues earlier last year - all good from what I was able to tell/measure with ohm meter. Will check the key switches for corrosion - that seems possible.

 

[PosessionSound26PC]

I should correct my original post - I think I have the 1989 motors, not 1988. I say this because the Merc manual shows my style of ignition amplifier (sort of pyramid shaped mounting bracket) on the "1989 Models - On" schematic.

 

[Bt Doctur]

How many batteries do you have ? Some are wired with the motors connected together

 

[nola mike]

Is that with key in run position, or start? Sounds like you're grounding the port ignition system. Guessing you screwed up the wiring somewhere with the solenoid/starter replacement. What are the common electrical points between the engines?

 

[PosessionSound26PC]

How many batteries do you have ? Some are wired with the motors connected together

Two batteries, one electrical system. I can start either engine with either battery.

 

[PosessionSound26PC]

Is that with key in run position, or start? Sounds like you're grounding the port ignition system. Guessing you screwed up the wiring somewhere with the solenoid/starter replacement. What are the common electrical points between the engines?

Hi Nola Mike, I'm pretty sure that was with key in START. I had Port running and went to start Starboard, cranked it and watched Port die. I changed out both starters and the slave starter solenoid for Starboard only but that was before I put her in the water in November for the test run - both motors were running for at least 20 minutes prior to Port overheating and us limping back to dock. Also, when I went to winterize both, Starboard started right up and and then wouldn't start again - something seems to have failed at that time but I'm not familiar with what part of the ignition system is downstream of the starters such that turning the key allows the starter to work but not the ignition system... Can something be grounded/shorted in the ignition circuit and still allow the starter to work? Coil? Ignition Amplifier?

I don't have a schematic for the wiring connecting the two motors so not entirely sure about common points. I have one of those Perko battery switches and usually have it on ALL. I also have an inverter for charging both batteries using shore power. Based on earlier electrical tests, both motors are connected to the same ground/neg and I can start either motor from either battery so assume common positive as well.

I'm heading back to the boat on Wednesday and will try some more troubleshooting - any thoughts are appreciated.

 

[Bt Doctur]

I have one of those Perko battery switches and usually have it on ALL
Being a twin you should have 2 battery switches, Switch is never on all except for emergency starting. For safety,one motor should be stand alone. Meaning it has its own battery and nothing else. The other can be used as starting and house
I have a 28 coastal set up with 2 perko switches. "C"' of each switch to starter, #1 to battery for port and the other #1 to stbd battery . #2 of both switches connected together , can also be connected to a house bank
Normal positions are 1 and 1 . Emergency start for either motor, 'Both" "Both"
If a house battery is included it now gives you 3 or 4 batteries to start a motor

 

[PosessionSound26PC]

I have one of those Perko battery switches and usually have it on ALL
Being a twin you should have 2 battery switches, Switch is never on all except for emergency starting. For safety,one motor should be stand alone. Meaning it has its own battery and nothing else. The other can be used as starting and house
I have a 28 coastal set up with 2 perko switches. "C"' of each switch to starter, #1 to battery for port and the other #1 to stbd battery . #2 of both switches connected together , can also be connected to a house bank
Normal positions are 1 and 1 . Emergency start for either motor, 'Both" "Both"
If a house battery is included it now gives you 3 or 4 batteries to start a motor

I have only one Perko switch mounted at the transom. When I changed the starters, I did voltage and resistance testing checks - both motors have the same negative/ground and regardless of which battery was connected, both starters had voltage on their main lines (so same positve as well). The batteries are mounted in parallel and they act as one big battery at 12v, with one inverter for both. By "For safety" do you mean use one battery for starting/motors and one for house so that you don't accidentally drain your starting battery while playing the radio/cooking/etc.?

 

[PosessionSound26PC]

I think I've sort of figured it out - One or both of my alternators may not be working properly or the belts are too loose or something is not right with charging. I bought new batteries last summer, installed them, and have topped them off w/ my generator and inverter once or twice while finishing up the starter work. When I took the boat out in November, Starboard had good charging voltage according to the gauge - that was the motor I did most of the work on. I don't recall looking at Port... but the belts on both were a bit loose and they made some noise as we moved at low speed (no wake zone). We never got up to speed due to the overheat problem w/ Port. Boat sat around December and when I went to winterize everything started fine but maybe the batteries were already low for some reason and that's why Starboard wouldn't start and why it killed Port when trying to start it with Port running.

I charged the batteries again today for about 45 minutes and Starboard almost started up - I think it would have if I had hit the gas a little bit - it wanted to at first. Port started up just fine, even after Starboard gave up, and unlike last time, I was able to bump the throttle a little higher on Port and turn Starboard over w/o killing Port (though it still didn't start). I didn't have time at lunch to fully charge the batteries so I will have to go back and try again later this week.

But definitely weak batteries for some reason and Starboard has a harder time starting than Port for some reason...

 

[Bt Doctur]

First fix the battery cable wiring and add a second switch so that each motor has its own battery
NEVER run twins on "All" because your most likely "bucking" the alt feeds or 1 alt has been disconnected already.

 

[PosessionSound26PC]

First fix the battery cable wiring and add a second switch so that each motor has its own battery
NEVER run twins on "All" because your most likely "bucking" the alt feeds or 1 alt has been disconnected already.

Could you elaborate a little bit on "bucking" and what you mean by "disconnected already"? This is the way the boat was designed (one switch), would take a lot of work to re-wire everything - not sure I have it in me. With the current set-up, it is advised to run on one battery? That's perfectly fine, I can do that, just don't see the difference...

 

[PosessionSound26PC]

@Bt Doctur - I think I see where you're getting at. After a bit of research I think I am wrong about how my boat is wired - it is likely something more along these lines (diagram):

2 Motors, 2 Batteries, 1 Switch

I will have to confirm this next time I'm at the boat this week. If that diagram applies to my boat, I am still unsure how the shore power/inverter is connected - is it connected to only one battery and I've only been charging that one?? That might explain why Starboard is not starting... out of juice. If shore power/inverter is connected to both, I am at a loss why Starboard isn't starting. Will confirm the wiring and report back.

 

[PosessionSound26PC]

First fix the battery cable wiring and add a second switch so that each motor has its own battery
NEVER run twins on "All" because your most likely "bucking" the alt feeds or 1 alt has been disconnected already.

Hi @Bt Doctur , see my second reply below yours - wasn't sure if you get notified by a regular reply

 

[Bt Doctur]

No, you need 2 switches one for each motor, "Bucking alternators" means both outputs are connected together, meaning you have one big single .engine. Some 'disconnect" one alt output on the back of the alt. again one big single engine

 

[PosessionSound26PC]

No, you need 2 switches one for each motor, "Bucking alternators" means both outputs are connected together, meaning you have one big single .engine. Some 'disconnect" one alt output on the back of the alt. again one big single engine
View attachment 374475

Pretty sure the diagram I linked to above does the same thing - it keeps the alternators from conflicting with each other as long as you don't set the switch to ALL (which is only used for low battery / emergency paralleling). Each motor has its own battery, separate from the other, even though they share ground. My boat came this way from the factory (Formula) so I assume they know what they're doing . Unfortunately, I didn't know that and have been running the boat on ALL. I haven't owned it long and have only taken it out about 10 times so not sure how much damage may have been done or to what. From reading about alternators, it sounds like the only real damage is that it forces the voltage regulators to constantly turn on and off because one or the other has a higher voltage than the other one at any given time. This puts extra wear/strain on the regulators.

I am going to confirm I have the layout shown in the diagram I linked to later this week and I will also recharge the system and see how it behaves again. I assume that setting to ALL during charging will charge both batteries but maybe this is not a good idea? Do you recommend charging each separately?

 

[Bt Doctur]

IF you are wired according to your pic, all the switch does is combine the batteries on "ALL,BOTH' and does not have the house charging. House will only charge on #1 or #2 ,
ALL,BOTH combines all batteries together. THe engine starter cable is connected directly to the battery for each engine so the switch position has nothing to do with killing a motor while starting the other