5.7l Mercruiser Starting Problem - Help!

Quigs

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Just when I thought I got all my little boating problems out of the way, yesterday I decided to make the most of the good weather and venture out for a bit of fishing.

Anyway, my boat always starts first time, without fault. However yesterday when I went to start, it almost fired but then just turned over and over. With a little advise from the marina guys, I opened the throttle to full, tried again and it eventualy started, almost although it had flooded.

Gave it a few minutes, tried again, no problems, did the same again, no problems, so felt safe to set off. Out fishing we moved around to a few various places and once more it happened. Didn't want to start until I put her in full throttle.

So, anyone with experience of this, is there an easy fix or do I now send in the engineers to tinker at more expense?

Thanks in anticipation.
 

jimmy_the_builder

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Do these have the oil pressure switch low down on the block? My 4.3 merc had this, and a dodgy connection to the sender had the same symptons that you are desribing. Clean the connection up and problem solved. (Apparently the purpose of this oil pressure switch is to allow the engine to turn over, but won't let it start until sufficient oil pressure is present to allow safe operation).

Cheers
Jimmy
 

RobWales

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Sounds very much like a flooding problem and one which I was more than a little familiar with on my last boat (same engine) only way I managed to solve it was a replacement carb=big bucks I'm afraid!
One thing you MUST check ASAP is that if she has been and is still flooding you will get petrol pissing into the combustion chambers running down passed the compression rings and diluting your engine oil = big big bucks!!!!!

Rob
 

Quigs

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EEEK - How can I check for dilution? I did forget to mention its the EFi model, not the carb model! Does that makes any difference?
 

ExcaliburII

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Wouldn't have thought oil dilution from a flooding carb would be a major problem - when the engine is running any excess petrol will get burnt; effectively it will just be running very rich with all the usual symptoms (hunting at low speed, big increase in fuel consumption, etc). Main problem will be difficulty in starting, but once the engine is running and up to temperature, any small amount of petrol in the oil should boil off very quickly. Bear in mind you'll be adding a max of a couple of ccs of petrol to at least 5 or 6 litres of oil. If more than that is getting past your piston rings, petrol in the oil will be the least of your worries /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif

Anyway, as it's an efi, it won't be a carb-related problem /forums/images/graemlins/confused.gif
 

Fire99

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Since its and MPi model, my 1st port of call would be an electrical connection (like the oil pressure switch mentioned earlier) especially since when running there are no adverse performance issues.
 

ExcaliburII

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If it's some sort of electrical/interlock switch type of problem, I would expect the symptoms to appear under normal running as well. For example, if there's something in the electronics that won't let the engine run if it hasn't got enough oil pressure and there's an intermittent poor connection on the oil pressure switch, every time the connection wobbled when under way I would expect the engine to stutter or cut out. Evidence appears to be that once it's running, it's fine. Edit: unless there's some clever electronics that only monitors the oil pressure when starting, perhaps.

I don't have any experience of failure modes of efi units, but gut feeling is that the symptoms given are unlikely to stem from that.

If there is a ballast coil arrangement on the ignition coil (ie it runs normally with a resistor in circuit which is shorted out when the starter is engaged to compensate for the drop in battery volts caused by the current drawn by the starter motor), it may be worth checking that out. If the ballast resistor is not being bypassed properly, the spark may be a bit weak when starting, which would certainly fit the symptoms. Could be that applying full throttle richens the mixture and helps it catch more easily, then once it's going all is sweetness and light again.
 
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