1996 Mercruiser 5.7 V8 LX EFI starting issue

I will continue trying to get to the bottom of this and think we can all say now that after the tests carried out yesterday voltage supply is likely the issue. All four batteries (marine grade leisure batteries) were replaced last year and have a 3 yr guarantee so no worries there to replace. Would there be a difference between a leisure battery and a normal heavy duty car type battery ? Anyway I will get onto changing it and checking terminals etc..

I think we’re almost there.
 
has anybody suggested removing battery connections and scraping the lead posts along with cleaning their clamps and greasing and refitting?
 
I am with Qbuoy on this I think. The one thing you have not done as far as I can see is trying the 'hard to start engine' with a known to be good battery which I would say is the first thing to prove before worrying about anything else.
Just because you bought it last year doesn't make it known to be good.
In my experience the cross over switch on an old boat may not give the full oomph from the other bank. Longer cable routes and seldom used switch contacts I suppose.
 
Last time I was at the manual you need at least a 110ah and serious CCA for these engines. Leisure battery would eventually not suffice at this. I think you may only just be getting by with the link out just now. But I’d urge you to think poorly of that port battery and bypass that entirely.
 
Noted on the port battery..... and the 110ah my intention is to try a brand new 110ah heavy duty same as the one fitted in my 4x4
 
Hi again all.......problem solved

Just to let you all know the conclusion with my starting issue as stated in post #1 it is a very logical one and with my limited electrical experience I think I would of been a long while finding it, however I did call in a reputable company with an electrical engineer and the problem was sourced and fixed in aprox. 20 mins. As advised by a lot of people on the thread to remove and clean terminals, check battery strengths , trace cables for kinks and loose connections etc. this was all done and all in excellent condition. Once the engineer arrived I was quite surprised he didnt want to hear the problem or witness it for himself, he simply understood my issue with the explanation I had gave him. he carried out a few tests and discovered the ground on the port engine was bad.....very bad. I explained that all terminals had been removed and cleaned from batter bank to starter motor. a couple of more ground checks later he asked me to fire the engine and hey presto away it went first time on the key. I obviously asked what the issue was and he said I had missed the large black ground wire attached to the back of the port engine which was literally corroded badly. So there you have it guys a bad ground, but Ill be honest , if you knew about that wire it would be an easy fix , but if you didn't (like me) its a major headache. I guess now I could offer someone else with that same problem some advice, and my advice would be that if you are not electrically minded or dont understand electrics .....bring in a motor electrician. I would have loved to solve this myself but with literally no electrical understanding at all I was blindfolded, the proof in that is that it took 20 minutes for the engineer to find and fix it. By having this thread and conversation on this site it could help someone at their wits end as I was.


I would like to reach out and thank every one of you for your help and supportive comments throughout this post to help me get to the bottom of this painful experience.
 
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