Volvo KAD300 surging 2700-2950 rpm

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East090

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Hi, I have a problem with my starboard engine (KAD 300), I have a Targa 34 with twin KAD 300's. The Port engine runs fine, but when I accelerate the boat when the starboard engine gets to about 2800rpm, its stagnates and then starts surging, gradually increasing to around 3000rpm. The after about a minute or 2 it jumps to 3100rpm and acts absolutely normally, wining to around 3600 WOT, its a little weaker than the Port engine but not a massive difference. If I bring the starboard engine back to below 3000rpm when i try and accelerate it goes through the same process of surging before acting normally. No smoke and no unusual noise, when sat at 3100rpm on both it runs at 32kts so what i would normally expect. Hull and props all clean, it happened before i pulled it out for usual yearly maintenance and problem remains now back in.

Any thoughts/help would be greatly appreciated, engines have done 770 hours and its a 2005 boat, always well maintained.



Many thanks.

Steve
 
East090 said:
I'd guess the turbo is knackered and you are not getting a clean switchover from supercharger to turbo. That is usually at about 2700. If you can get the turbo spooled up enough ,it would run, albeit not properly, and not a clean acceleration. When you throttle back to 2700-2800, you are back in the same problem area between the supercharger working and the turbo not really working! Tho you suggest it is at a bit above 2700, or so that it surges? If one turbo has failed the other will be about to , so get both of them sorted.
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Could be a fuel restriction but given the particular engine revs when the problem occurs it's most likely tired turbos.
One engine may seem OK but it wont be far behind. The relatively good news is turbos for KADs are not too expensive and fairly easy to swap.
The exhaust housing corrodes way and the tips of the exhaust impeller shrink back so the turbo looses boost pressure with age.
 
I had thought about the boost pressure sensor, not sure where it is and how easy it is to swap over with the 'good' engine, to test that? Is it worth trying, if so is it easy to find and do?
 
I think the inlet manifold pressure sensor is built into the ECU unit that is part of the fuel filter mounting etc. It is connected to the inlet manifold by a small diameter plastic pipe - which are generally very reliable etc.
I wouldn't recommend swapping the ECUs over or trying to get the sensor itself out of the ECU - that's a lot of work and complication to unravel.
The engine behaviour you describe is very typical of all KA(M)D engines. If you can find a friendly service engineer with a VODIA diagnostic box they can read out all the pressures etc.
 
East090 said:
Hi, I have a problem with my starboard engine (KAD 300), I have a Targa 34 with twin KAD 300's. The Port engine runs fine, but when I accelerate the boat when the starboard engine gets to about 2800rpm, its stagnates and then starts surging, gradually increasing to around 3000rpm. The after about a minute or 2 it jumps to 3100rpm and acts absolutely normally, wining to around 3600 WOT, its a little weaker than the Port engine but not a massive difference. If I bring the starboard engine back to below 3000rpm when i try and accelerate it goes through the same process of surging before acting normally. No smoke and no unusual noise, when sat at 3100rpm on both it runs at 32kts so what i would normally expect. Hull and props all clean, it happened before i pulled it out for usual yearly maintenance and problem remains now back in.

Any thoughts/help would be greatly appreciated, engines have done 770 hours and its a 2005 boat, always well maintained.



Many thanks.

Steve
Click to expand...
Worn turbo on the exhaust fan side it's not delivering enough boost so the super charger cuts back in .
You could have a slipping prop on one of the drives too .
 
First thing I would check is the main belt from the crank up to the waterpump, as when the compressor cuts in it loads the main belt causing it to slip if its not tight then the revs fall and rise as the compressor loads and unloads the main belt.
 
volvopaul said:
Worn turbo on the exhaust fan side it's not delivering enough boost so the super charger cuts back in .
You could have a slipping prop on one of the drives too .
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Thank you, I think the drive clutch is just about gone on that drive as its an extremely 'soft' engagement when I go to drive from neutral, I also had signs of water in the drive oil so I as the drives are coming off this winter I was getting it fully serviced and clutch replaced... could that be causing the issue? Or have I got the meaning of slipping props wrong? Sorry I hadnt thought it could be conected to the drive issues.
 
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