QBhoy
Well-known member
What boat and engine is this ? If it’s similar, I’d be suspecting turbo or fuel issues
Volvo penta ad31 power
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sogood
Active member
It's a Sealine 218 with an ad31, an a 290 dp outdrive. The turbo has been professionally rebuilt as was the fuel pump. New injectors, fuel tank removed and totally cleaned out, via new access panels on top. New filters etc. etc. etc. You name it I've done it! I suspect a leak somewhere in the fuel system so that it's sucking air. Trued it on a remote tank, no change, and for what it's worth, I have no fuel at all on the return line, which I've been assured isn't unusual at all.
James jameson
Member
Have the outdrive Gear ratios in the drives checked in boat instances ?
QBhoy
Well-known member
Ah. Lovely boats. I had a 4.3 218 for years.
Anyway…if you were sucking air…I think you’d know all about it. You’d probably need to bleed constantly. The injectors too I’d think.
I had an issue with fuel delivery on my 218. It would run seemingly ok at lower rpm…but as soon as I put some load on her and a higher fuel demand…it wasn’t happy. After messing around a little, it ended up being the non return valve in the fuel line getting clogged. I think the fuel isolation valve also had restrictions too. Could be the case for you too. Are you blowing black smoke when this happens or not ?
sogood
Active member
Géar ratio is correct. 2:30 or 2:32 as per volvo spec with the ad31 and 290 Dp combo. I checked it manually using the suggested method and it all checks out. I've not given up on it as I have a few minor things to check out.
sogood
Active member
Non return valve OK. No change when it was removed. No black smoke. Revs up to 4000 no problem when in neutral. Just not happy under load.
sogood
Active member
I only get about 7 knots max out of it as it stands.
QBhoy
Well-known member
Ok. Surely the very unusually pitched props then. The same ratios on an s25 sealine with a more powerful kad32 runs A4 props usually. A5 at most under the owners request. Been aware of other boats around the 24/25ft size with your engine and drive that also run a4’s. A7’s are just way too much pitch for certain.
QBhoy
Well-known member
Could be your fuel pump then. Wouldn’t pay too much attention to what it does in neutral though. Some engines will rev up to their max rpms in neutral, with only half their cylinders firing even. Silly of me to ask…but nothing to do with the outdrive trim position or similar ? Believe it or not…some guys have been known to only look at the gauge as a reference…and not what’s going on out the back end..not noticing that the outdrive isn’t all the way down and throwing water upwards out the back. She’ll never plane in that case ?
sogood
Active member
Mine is fitted with A6's. I ran it with A3's or A4's (can't remember which) but with no change to performance at all, despite being assured that it would cure all my ills.
sogood
Active member
Performance has been "measured" with outdrive in various positions, with only very minimal change in performance. Nothing of any consequence. Fuel pump has been professionally overhauled and rebuilt.
QBhoy
Well-known member
Yours isn’t likely a prop issue I’d be almost sure. Given the above. More likely a fuel issue or turbo/elbow issue I’d be sure. Have you made certain the fuel pump is good ? Injectors ok ? Fuel filter is set up with fuel flowing in the right direction? I worked on a nimbus with this engine recently. It had the exact issue you have. Went through the usual things…then noticed the fuel supply pipe was going into the outlet of the primary water separating fuel filter. Swapped the lines over…problem solved
sogood
Active member
I'll look at the fuel lines when I'm at the boat again over the next few days. Thanks for the input and apologies if I've hijacked the thread.
QBhoy
Well-known member
Yeah. Worth a look. The result on the nimbus was literally as you describe. Just hit a wall around 2000ish rpm. No black smoke from turbo to indicate it was over fuelling or likely getting enough fuel. That’s what gave it away for me. Normally if the fuel supply was healthy enough and hitting a wall for power…these things will belch black smoke indicating the issue is elsewhere and usually lack of boost/aspiration. Good luck.
sogood
Active member
Thanks. I'll keep you posted.
sogood
Active member
Just a thought but given that I ran the boat from a remote tank, fed directly to the lift pump, with no improvement, wouldn't that remove the fuel filter /water separator from the equation?
A_8
Active member
I would listen to this and it's an easy first check, take off the exhaust knee and use your fingers to try and spin the turbo, it should spin freely without much resistance.
sogood
Active member
Thanks for the input but as per a previous post, the turbo was removed and overhauled/rebuilt and is spinning freely.
stelican
Well-known member
Have you checked the turbo is spinning