strange electrical starting fault

1eyedjim · 23 March 2015, 12:19

Hello

wondering if anyone could give me some help on a strange fault i am getting on one of my boats

It has a Mercruiser 5.7 v8 and alpha 1 leg.

starts up well and runs lovely, turns over slightly slower though than my dads with the same setup but 5L engine.

i have been taking the boat out and it runs as it should, i just need to tweak the interrupt switch on the engine as occasionally it stalls when going into reverse. it has 12.5v when off and 14 when running but when coming in to dock if the boat stalls it will start but if it stalls again then it turns over really slowly and wont start. i then turn it to run on both batteries and it spins over rapidly.

this happened Saturday, i got the boat moored up turned it to the battery i had the problem with and it wouldn't spin over hardly. then left the boat for half hour tried again and you would never know there was a problem.

has anyone had this before? i have now changed both batteries twice and the issue is still there so no im wondering if the battery cables are breaking down and giving high resistance after running the boat. i will be changing these next week anyway as they are solid and cannot bend them plus are what came on the boat and being a 1996 its probably not the worst idea to replace them.

the batteries fitted are about 3-4 months old

if anyone has any advice it would be good to hear.

yam man · 23 March 2015, 12:33

Check all connection ie earth an positive are clean . An if interruption switch is holding when going in to gear sound like a shift cable fault . Also is the battery cable the right size could be loosing voltage due to load

Poly · 23 March 2015, 12:35

if its not the battery, then the cable between the battery and the switch is a possibility - but so is the switch. These 1/2/both/off switches are notorious for failing (corrosion?).

1eyedjim · 23 March 2015, 13:12

cheers for the quick replies,

Yam man - earth has been cleaned about two weeks ago, i believe the battery cable is correct as was from the factory. the shift wable was replaced 12 months ago but the boat has not had much use since, could it just be it needs using or that the cable is no good?

i didnt think to much about the switch, i took it apart and its in a place where it isnt wet and tbh looked the cleanest part of the boat but will bear this in mind.

thanks for the help, glad i seem to be on the right path and always good to have it confirmed.

cheers

Jim

jambo · 23 March 2015, 13:24

Don't know if it helps but I had trouble starting a few years ago and it was the cables from OB to battery which was in the consol and in the cables were routed under deck trunking I renewed and what a difference. For the price of cables worth a try.

Sent from my iPhone using RIB Net

Lee argyle · 23 March 2015, 18:07

Bypass the current + & - battery leads and cutout switch with some jump leads, If the problem disappears you've narrowed down the fault

jyasaki · 25 March 2015, 16:18

Or wire in a temporary voltmeter at the motor. Sounds like a low voltage condition when cranking.

jky

1eyedjim · 27 March 2015, 23:48

What sort of thing would cause this?

jyasaki · 28 March 2015, 16:58

Low voltage at the motor while cranking, most likely. Once you verify that (and make sure it isn't the actual battery dropping voltage), you need to work back towards the battery and see exactly where it's dropping.

jky

steco1958 · 28 March 2015, 20:38

Sounds like you may have a loose/high resistance connection, this could be either + pos or - Neg, cables.

Check all connections first, undo and clean, remember to grease each connection.

Bigtalljv · 28 March 2015, 21:01

Another vote for connections and cables.

I rebuilt and old truck and put in a new wiring harness and had issues with it dying while driving and not starting sometimes. Turned out the barrel on the crimp to the main feed was cracked but the heat shrink held it in place most of the time.

When testing it id see the voltage come and go as I tugged on the cable and it wiggled the busted connection. Ended up actually piercing the cable in a few spots as I thought it must be broken internally before I realized the pulling and pushing made the voltages change.

I also had ground issues as I'd painted and powder coated every surface including those they used as grounds.

Jason

Festinghouse · 28 March 2015, 21:17

personally i think you have two problems, one is cutting out maybe due to running a bit lean? the other i think could well be starter motor brushes. i had similar slow starting and turning over issues, but because it would work at times i wrongly assumed that the starter was fine. was only when it packed in turning over all together that i took it off and once stripped i found two of the four brushes were knackered

Nightfisher · 10 April 2015, 07:24

You might check: Starter (use a draw tester (s/b 175 Amps max), or Engine Timing (not advanced enough) or Running hot.

Quote:

Originally Posted by 1eyedjim

Hello

wondering if anyone could give me some help on a strange fault i am getting on one of my boats

It has a Mercruiser 5.7 v8 and alpha 1 leg.

starts up well and runs lovely, turns over slightly slower though than my dads with the same setup but 5L engine.

i have been taking the boat out and it runs as it should, i just need to tweak the interrupt switch on the engine as occasionally it stalls when going into reverse. it has 12.5v when off and 14 when running but when coming in to dock if the boat stalls it will start but if it stalls again then it turns over really slowly and wont start. i then turn it to run on both batteries and it spins over rapidly.

this happened Saturday, i got the boat moored up turned it to the battery i had the problem with and it wouldn't spin over hardly. then left the boat for half hour tried again and you would never know there was a problem.

has anyone had this before? i have now changed both batteries twice and the issue is still there so no im wondering if the battery cables are breaking down and giving high resistance after running the boat. i will be changing these next week anyway as they are solid and cannot bend them plus are what came on the boat and being a 1996 its probably not the worst idea to replace them.

the batteries fitted are about 3-4 months old

if anyone has any advice it would be good to hear.

1eyedjim · 20 July 2015, 13:12

just to put this to bed if anyone reads it in the future,

i replaced the battery cables and now it runs like clockwork so was just bad cables

jyasaki · 20 July 2015, 16:22

Thanks for the resolution report.

jky

Nightfisher · 26 July 2015, 07:52

Did you consider overheating? Take-it you have a working temp gauge..just seems that type of problem that solves itself after cooling down points toward an overheat condition or possibly the engine timing is too far retarded? Good luck.

1eyedjim · 27 July 2015, 01:43

Boat has been used for last few months since changing cables and not missed a beat

Not overheating as gauge sits perfect where it should and ignition was changed and I set it up bang on and checked a few times

The cables was knackered when they came off. Brittle as anything and the lug that went on the starter had cracked

As I said above. It's been fixed so not looking for anything else