Engine issue

[cem]

Been a while since I have posted so I thought I would open e season with a question about a problem we have

Looking for ideas as to what the problem could be with our engine, up to 6kts no problem between 8 & 15kts we get a popping noise, miss fire, sounds like a car back firing but not as loud, ( initially it was loud)

Engineer (one of the better ones at cobbs quay) has looked at it, the boat had been serviced and de winterized, they then found it needed a new distributor cap and ignition sensor, took it out for a test run and called me to say all is ok...... It's not!

Yesterday we had a run out problem happens maybe only 4 or 5 times, today it was almost worse than it was when we discovered the problem , so I am £250 down and the problem is as bad is it was

Anyone got any ideas what could cause this

Engine is a 5l V8 mercruiser

 

[jpw]

Hi CEM,
I had exactly your symptoms with a 5.7 Merc V8. Turned out to be a burnt valve.

I would suggest that before you spend any more, you have a compression test done. Hopefully you will get 8 even compressions and can then rule out 'my problem' which involved a head off job...

Good luck
James

 

[beejay190]

Been a while since I have posted so I thought I would open e season with a question about a problem we have



Engineer (one of the better ones at cobbs quay) has looked at it

so I am £250 down and the problem is as bad is it was

Sorry to read of your problem.


Who is this engineer then ? Should I use him or avoid him ?

 

[dustywings]

I had the same problem years ago and spent ages trying to get to the bottom of it . Eventually turned out to be the coil, a new one cured it instantly.

 

[mtb]

If you can run the engine at night under load you may see electrical sparks re ht side of things breaking down
The old fashioned way to test the high tension side of things would be to disconnect the ht leads and see if it causes the spark to jump, if you do try this be sure to have insulated tools
I reckon the loud cracking is a spark jumping to earth
cant see it being a burnt out valve or pinking due to pre ignition or carbon build up
cheers
mick

 

[Drewster]

I had the same problem years ago and spent ages trying to get to the bottom of it . Eventually turned out to be the coil, a new one cured it instantly.

This is more likely to be the fault totally agree

 

[cem]

Thanks for the reply guys, I am hoping it is not the burnt valve! That sounds like it could get expensive

Not going to name the engineer especially as I have not been able to speak to them as yet, happy to pay for the work to be done and they will feel the wrath if they try and screw me around, but until they have had an opportunity etc etc

When all is sorted (or not) I will give em a name check

 

[gordmac]

If it misfires under load but runs ok not loaded it is probably an electrical problem, plug leads or cap, possibly coil. Has it got electronic ignition? Generally you wouldn't hear anything with an electrical problem, visible if reasonably dark. Popping noise could be a burnt valve but it isn't loud like a backfire. Backfires are unburnt fuel burning in the exhaust, fuel can only get there if it isn't burnt in the engine.
A compression check would be worth doing, even if it only gives you peace of mind. Easy to do yourself but I wouldn't think a mechanic would charge much.