Engine problem (bit long)

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KevB

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A Large beer for anyone who can shed some light. It's driving me crazy.

I have two kad43's which are in excellent condition and serviced less than 15 hours ago.

Here is the problem.... The first couple of trips after the boat went back in the water from it's winter lay up everything was fine, no problems at all. Then a couple of weeks ago on the way to Yarmouth from Chichester (the forum get together), a couple of miles off Yarmouth (sea choppy and third full tank of fuel which had been in since early december and during winter lay-up) the engines started to lose power pulling no more than 3000 rpm. My initial thoughts was that it was just one engine but it's both. I slowed down and had a look around including looking to see if I had picked something up on one of the legs but nothing out of place. Started engines and everything seemed fine for the last part of the journey.
Left Yarmouth a couple of days later and again everything seemed fine until I was approaching chichester harbor when the same happened again.
At this time we were fairly low on fuel so filled up when back in chichester (so full tank of fresh fuel).
Since then the engines wont rev past about 3000rpm when in gear and more often than not wont go past 2600.

These are some facts and what I have tried...

There is no sludge or water in the water separators.
Cleaned secondary fuel filters.
Replaced primary fuel filters (even though the ones on there were less than 15 hrs old).
Checked for blockage on the fuel tank breather pipe incase a Vacuum was being created in the fuel tank.
The engines will run to max revs when in neutral
When first opening throttles in gear the engines rev as normal the boat gets up on the plane as normal, the engine revs are climbing 3500, the boat is leveling out but within about 20 seconds both engines note changes and they start 'hunting' and the revs slowly drop down to anything between 2600 and 3000 rpm.
Anything below 2600 and everything is fine, they sound perfect but go above and they start 'hunting'.
If I slow down to tick over and wait 30 seconds and open the throttles again all the above is repeated, they rev fine then slowly reduce revs.

I've tried each engine individually and they both pull the same amount of revs @ about 2650.

Now here's the weird thing. If I turn sharp to the left the engines revs increase a bit, say about 200rpm. If I turn to the right they decrease by about 500rpm???


I'm totally confused. If it was poor fuel then why would the boat pull away fine then slowly loose revs? the same goes with blocked filters etc....

Each engine has a separate pickup from the fuel tank so the only thing in common with both engines is the tank and the fuel.

Any suggestions welcome.
 
try running with the fuel filler cap removed to totally dis-count poor venting. use some arrangement to stop water getting in temporarily, or get a permit from the harbourmaster for speed trials in emsworth channel ( easy enough)

are the fuel pickups both on one side of the tank?
 
From previous posts on the PBO forum, I wonder if this might be of help.....

PBO

Certainly something to try before shelling out loads of dosh.

The whole thread is HERE
 
Hi Andy,

I've checked the tank breather and it's clear. I did run with the fuel filler cap off and it made no differnce.

I feel it is fuel starvation but can't pin point where or how.
 
Well, the tree I'd be barking up is fuel starvation. This tree has two branches:
1. partial blockage in fuel supply somewhere common to both engines.
2. air being sucked in with the fuel supply somewher common to both engines

Of those two I'd start with looking how air might get in. Filter seating etc
If you have a slight air leak, say around a filter seal, then it might only be provoked to suck in air when a large amount of fuel is being sucked by the engines, creating a strong vacuum. This putative leak could conceivably get better under a sharp left turn and worse under a right turn
 
Could be a partial blockage from the fuel pick up pipe in the tank. Suggest you get your dinghy pump and blow air back through the fuel line, should be able to hear the bubbles coming out in the tank. Sometimes there's even a filter in the tank pick up, hope that's not the case as it can be a [--word removed--] to change.

As for why it makes a difference when you turn one way or the other, again it could be the partial blockage falls away but then gets sucked back up again.
 
RustyKnight,

Thanks for the link.

I can only guess that maybe the problem is with the fuel intake pipes in the fuel tank. But I'm having problems convincing myself it's happen to both engines at the same time. (each engine has seperate pickup)
 
OK

I'd try to avoid relying on the presumption that 'it's both engines, the only common factors are the tank & the fuel, so it must be one of those...'
I fault-found both electrical & mechanical awkward bu**er problems for a living & soon learnt that unlikely coincidences occur with quite surprising frequency.
 
any chance of rigging a temporary supply for testing that doesn't use the fuel pickups? or beg/borrow a suitable pump & prove that the pickups allow adequate volume of fuel to be drawn same/more than max fuel use of one engine?
 
If the fuel stuff appears OK, then you ought to look at the air supply ....

Have you checked the air intake filters ??

Turbo's/Compressors running OK ??

Next one to check out is the exhaust bend to see if there are any restrictions there ... gunk builds up where the cooling water meets the hot exhaust and restrictions there may cause too high back pressure in the exhaust system ...
 
I agree. The man who doesn't tighten up the filter on the port engine sufficiently, thereby allowing an air leak on that engine might not tighten up the filter sufficiently on the starboard engine either.....just an idea
 
Don't forget to add to the list of Facts:

This first happened during that rough trip to Yarmouth for the forum meet and it came on suddenly but cleared the next day on the way home. Well until you reached Chi Bar.

Get your fuel tank cleaned out by one of those pro cleaners, there were some large bits in your primaries and there could be some even larger bits in your tanks.
 
Thanks to all for your suggestions (Vagabond excluded and I'll be posting a picture of you high and dry shortly).

I've checked seals, bled fuel system for air, tightened nuts, cleaned and changed filters. Checked for blockages in breather, air filters were changed less than 15 hours ago. Engines are only 4 years old and used regularly (600 hours). The only thing common to both engines is the fuel and the tank. Fuel is clean and no signs of sludge in primary filter. I think I'm telling myself as others have suggested that the problem coincidently is with the fuel pickup and happened to both pickups at the same time....
 
I would take off for inspection one of the engine filters.

I would check that it is full of diesel and not only half full.

I would tip into a clear jam jar and wait for 10 mins to see what settles.

I suspect water has semi emulsified in the bottom of your tank.(certain fuel additives can do this and even if you havent put anything in, the fuel could have been treated before you got it).

You can unscrew your pick ups and wedge them half way up your tank so out of the muck. Then try.

Can you get a thin pipe into your tank to suck from the bottom ?
You should be able to get in from the Fuel sender or pick up but you need the lowest point.

The emulsified water will rest at the lowest point and be held by baffles which could explain the tight turns .
 
i am unhappy that it is fuel. Cos it's so exact. I wd take off air filters and try that. Fuel blockage isn't on/off as decribed is it? - the moment the fuel is blocked the thing uuurrrrr slows down a lot - it doesn't click back on song below 2600, imho.
 
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