Volvo penta ad31 power

  • Thread starter Thread starter CBC
  • Start date Start date
sogood said:
I have the same ptoblem, with A6 props. These were on the boat when I bought it. I tried A3's with no change except that the revs got slightly above the 2000 RPM I had been maxing out at. Everything has been refurbished, cleaned or replaced with no change. I feel your pain.
Click to expand...
What boat and engine is this ? If it’s similar, I’d be suspecting turbo or fuel issues
 
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.
 
sogood said:
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.
Click to expand...
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 ?
 
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 said:
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.
Click to expand...
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.
 
sogood said:
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.
Click to expand...
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 ?
 
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.
 
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.
 
sogood said:
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.
Click to expand...
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 said:
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.
Click to expand...
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.
 
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 very long overdue update to the above. I've used the boat occasionally with the issue present and then took it out of the water to do some repairs, antifouling etc. I put it back in the water only last week, determined to finally get to the bottom of my "low power" issue. I still felt sure it was fuel related, either volume or pressure. So today, as a step in that direction, I put a priming bulb on the fuel line, between the main fuel filter/water separator and the lift pump. I primed the filter and squeezed the primer bulb until it became hard, as per normal function. I fired her up and took off down the bay, hoping to see any sort of improvement over my usual 8mph max, thus assuring me that I was heading in the right direction. I throttled up and the speed increased, with the revs passing my usual 2k RPM, and continued to climb along with speed! I heard and felt the turbo kicking in, which had never happened before, as I never got to the required 2.5k RPM. I continued accelerating under I eased off at 22.5mph! This was at about 3kRPM. To say I was blown away would be an understatement. So now a more permanent fix is on the cards, by replacing the primer bulb with an electric fuel pump and an inlíne non return valve. I discovered a lot of owners on here were experiencing the same problem with low power and maybe this might prove to be a very cheap and simple cure. Happy days!
 
You must log in or register to reply here.

Share this page

Top