kad 44 issue at high revs

[rlw]

Hi all,

I've got a bit of an issue with my one of my kad 44's on a targa 40. At around 3000 revs the starboard engine seems to hunt sometimes. Never use to be a problem.
Had turbo's replaces last year and had the issue later in the year. Ask a tech to look at it but could not replicate the problem during the test run.

Engines run fine at lower revs. Feels like the boat looses power then immediately surges back. This then cycles. Was wondering fuel but if I crank it up to wot is goes away. Was wondering if it was the supercharge cutting in an out but would have though the were disengaged at 3000RPM. Port engine behaves normal en the boat goes onto the plane well. WOT is a bit to low at around 3500 with a full tank. Was advised against dropping down a prop size as the boat ran well.

It seems to be a spot in the early planing range. Went out last weekend on the river, had the issue on the way back sweet as a nut. Only thing iI can think of is I had more revs on.

Be gratefull for some advise where to look as I would like to sort it before the summer holls in case we go out to sea.

Rob

 

[Yabs]

Hi Rob,

I had a very similar issue on my Targa 40, when I first got it (also Kad 44's). One engine would tend to fall back on rpm around the 3000rpm mark, just in the area of Supercharger to Turbo handover (I think the Superchargers cut out about 2800rpm). Mine was solved by replacement turbos. A boost pressure check at the time identified slight pressure discrepancies between the two engines. Does seem strange as you have replaced Turbos already.
What size props are you running? You should be achieving 3700 - 3900rpm at WOT.

 

[rlw]

Hi yabs, I am running C4 props which are original but I think these add to the problem as the boat does not get to WOT. What props do you run?

 

[Yabs]

Hi Rob, my props are C3, on DPE drives with a 1.68 ratio. Originally it was fitted with B4s but I could only make about 3600rpm. The C3 propellers made a massive difference. I get 3800 - 3900rpm about 24-25 knots cruising at 3400rpm and 31 knots at WOT.

Regards
Yabs

 

[rlw]

Thanks Yabs, I was leaning towards this but the local tech told my to renew the turbo's first. Now for some C3 props at a good price!

 

[volvopaul]

Thanks Yabs, I was leaning towards this but the local tech told my to renew the turbo's first. Now for some C3 props at a good price!

You will find its more likely the worn turbo fan on the exhaust side and corroded housing . Why do people make wild guesses , you need to test the boost pressure first under load before you start spending money guessing what could be wrong . If the boat has its origin props then why change them for a lower size? It's the engine that is at fault not the props.

 

[rlw]

Hi Paul,

Turbo's were replaced last year as the old ones indeed were down on boost pressure. (brand new ones) Engines ran fine with full boost but did not achieve WOT.
Hence the leaning to C3 props. Later that year the surging appeared. I had a volvo tech come in but could not replicate the problem when he was there. Tested more last weekend and I think the problem only occures 3000 -3300 reves. Looses revs for a split second then bounced back up. You can feel the boat loosing power.
I agree regardles of the props there is an engine issue. However as I was not getting WOT even with the new turbo's I was wondering if I was adding to the problem somehow. I was mainly hoping to gather some more ideas so I can test and hopefully have a more constructive session when I get the engineer in.

Rob

 

[rlw]

Hi All,

Had a session with an engineer from the local VP dealer on friday . After extensive testing we narrowed down the powerloss to a very specific rev range 3200-3300. At 3000 RPM the boat runs fine. Also at WOT. Straight accelleration to WOT is fine to however if we bring the engine RPM to the 3200-3300 range it starts hunting. The engineer reversed the throttle cables on the EDC control to see if the problem followed but it remained so the controls should be OK. Seems convinced it is an electronic problem but has never come across this. Now checking with volvo. Next step would be to replace the ECU but at this stage he is guessing so would be interested if VP or anyone on the forum has come across something similar. The only long shot that I can offer is that it could have started last year after a software upgrade when checking out the boost pressure. Not sure if this is realistic though. He did have a case on a KAD 43 where the stop solonoid was triggered but the engine cut out completely. It does feel like the engine cuts out for a split second an then goes again. Any thoughts on where to go next would be appreciated.

On the plus side I now know all works if I stay out of that specific rev range. Do want to get it sorted though.

 

[tinkicker0]

Before spending big bucks I'd be looking at the lift pump and filtration first if it were my boat.

 

[AdeOlly]

I have had a very similar problem twice on my boat. I'm running KAD300s rather then 44s, so not sure if the electronics are the same. First time the issue was nothing more than a dodgy turbo boost pressure sensor feeding duff info to the ECU and causing the engine revs to yo-yo around. This did not raise a error on the EDC. Failure of these is not uncommon I was told, and due to corrosion caused by condensation.

The other problem I had on my kad300s was intermittent loss of power at 3000-3200rpm with revs dropping back to 2600, then surging back a few seconds later. That also turned out to be electrical (throttle pot). IMO always validate the electronics before taking anything to bits!

 

[rlw]

Throttle pot seems to be OK as we reversed the controls and the problem stayed with the engine. Tech thinks boost sensor is ok but on the list to replace if nothing else is found.
Latest feedback from Volvo is that it could be the lift spring in the stop solonoid. Will also push to have the fuel system checked just in case.

 

[volvopaul]

Throttle pot seems to be OK as we reversed the controls and the problem stayed with the engine. Tech thinks boost sensor is ok but on the list to replace if nothing else is found.
Latest feedback from Volvo is that it could be the lift spring in the stop solonoid. Will also push to have the fuel system checked just in case.

Some years Back this problem reared its head to the point the topic was used on the EDC kad 300 trading course as a question in the end of week exam. I'd be looking at the spring and plunger for sure as it weakens the fuel suction pulls down the plunger stopping fuel getting to the head of the pump. Simple fix if it was that and by the sound of it it could be.

Have you pulled injectors for test?

 

[rlw]

Hi ¨Paul

Sound like we may be on to something. The injectors were done last year or the year before so they should be ok unless there has been an issue.
There was a very small amount of water in the filter but not enough to cause trouble according to the engineer. Will be checking out the tank.

 

[nick5798]

Hi I know this was a few years back but I am having the same issue do you know what the outcome was. Many thanks

 

[volvopaul]

Hi I know this was a few years back but I am having the same issue do you know what the outcome was. Many thanks

The answers are in this post . Start with wear on the turbo

 

[nick5798]

Even though the turbos had been recently replaced over a year before