Volvo Running Rough

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alb40

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A friends boat has a bit of a problem with its engine: A volvo A260A - 260hp 5.7 V8 petrol jobbie.

The problem is it is running very roughly. It will start fine, but in gear, it will vibrate alot as if its only running on half its cylinders, and misfire at anything above about half throttle, with lots of popping noises and eventual dying. It wont tick over very well either, but does run on a fast idle, albeit roughly as said before.

Out of gear, it coughs when ticking over, so that rules out prop fouling. Ive checked all the wiring connections, plugs, dizzy etc. and cannot find anything out of the ordinary.

It ran fine on its last run a couple of weeks ago, so has anybody got any idea on what else check up on?

Points / condensor can be ruled out BTW, as it has been fitted with electronic ignition.

Thanks

Alex /forums/images/graemlins/confused.gif
 
Thanks Alb for your comment on my post above, appreciated. I would look at timing ? - check vacuum advance pipe to dizzi - if thats perished or leaks it won't help. New plugs works wonders - made mine go (eventually) although their sods to get at. Might be worth checking for water in the fuel as well as a general once over for blocked jets etc. although my limited experience with big V8 car engines is that these things are so big any bits of muck just go straight thu - hosepipe like. Too rich / lean ? check a plug for colour. My monies on it being a spark / leccy problem though.
Good luck !
 
Thanks Alec. Ill check that too.

Ill be helping out with the repair of the steps down into the boat, so we will pop the inspection cover off the tank while we're down there.
 
Would suggest first find the cylinders that are not firing, run for a v.short time and get somebody else to touch the exhaust manifolds at each outlet. The yelps will tell you which are hot (Good) and which are not. if 2 are next to each other in the firing order suspect cracked dist cap.
 
I don't think you will find vac advance on any marine petrol engine as you never get high enough vacuum for it too work, ( I did a post on this some weeks ago).
First check its not something basic like water in the fuel, and check that the carb is delivering enough, you can look down the venturi and see if the acceleration pump squirts extra fuel when you snap the throttle open, also you should see if the is fuel being delivered from the carb jets as you take the revs up. stand back though just in case it backfires through the carb or you could need new eyebrows!
If you are sure the fuel is OK then check you don't have an air leak on the carb mounting, its unlikely to be a leak on the inlet manifold gasket but you can check as it would have vacuum on the breather hoses instead of pressure.
Are compressions OK and are the plugs the right colour, pale brown, if they are white then its too lean, if black or sooty then too much fuel, if only a few are discoloured then I would suspect ignition components, you say that the dizzy and leads are OK, I assume you checked the rotor? The other thing of course is the coil, if I remember Volvo use a ballast resistor coil where the coil normally runs on 8-9v but under cranking it gets the full 12v check the voltages at the positive terminal cranking and running. It could be the coil is getting too many volts and overheating and breaking down.
You could just swap the coil to eliminate it.
One other thing is the engine worn, we had one once which had so much blowby gas from the crankcase that it literally gassed itself and wouldn't idle, if we removed the breather hoses where they attatched to the flame trap it picked up and ran better, but it was knackered. Seen this on a couple of VP petrol engines.
Hope this helps.
 
Thank you for your comments.

The engine is totally worn out - up until last month when it was last used, it was running very well.

It seems alot of investigation and trial and error will be required. Ill start with fuel...

Cheers,
Alex.
 
In addition to Spannermans suggestions, I have seen a few V8s with broken valve springs (or even stuck valves, normally take more than 2 week though) which can cause misfire and popping.
 
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