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| Lost 10mph Volvo Penta 8.1L Gi https://www.smwebhead.com/phpBB3/viewtopic.php?f=11&t=23381 |
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| Author: | alanderson74 [ Sat Jun 08, 2019 12:18 pm ] |
| Post subject: | Lost 10mph Volvo Penta 8.1L Gi |
Any thoughts as to what could cause a 10mph top end loss? Engine is not mis-firing or stumbling, starts right up, idles smooth, full throttle RPMs are between 4200-4300 rpms. Slow to plane, it used to get up and out of the hole quickly...and RPMs only slowly pick up. Feels like the boat’s dragging or really weighted down. No water in the engine compartment. Top end is usually somewhere around 48 mph but we can’t get over 36 mph. Oil pressure’s fine, new oil, running perfectly besides the power loss. Steering feels stiffer than usually and possibly there’s a loss of responsiveness/directional control while reversing. Thoughts on possible issues to troubleshoot please... TIA |
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| Author: | Raft61 [ Sun Jun 09, 2019 4:35 am ] |
| Post subject: | Re: Lost 10mph Volvo Penta 8.1L Gi |
Is the power trim working? I had faulty rams once and even though I could hear the trim pump working nothing was happening. Also when in reverse, the leg would lift and reduce the amount of control I had. |
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| Author: | alanderson74 [ Sun Jun 09, 2019 10:49 am ] |
| Post subject: | Re: Lost 10mph Volvo Penta 8.1L Gi |
During our testing yesterday we tested trim tabs and drive trim - both functioned normally What about a prop issue - being a duo prop, could something be stuck somewhere we can’t see without removing the prop? My son did get a rope caught in the prop the last time out? Do duo props suffer from “spun prop”? I believe I saw somewhere that they are solid... ? While testing yesterday the throttle did not give the engine additional power from the half way engaged point to full throttle. There was no discernible increase in power or RPMs from the half throttle to full throttle. Fuel pump possibly bad? Although engine starts right up, is completely smooth... no stumbling or stalling. In neutral the engine responses as it should, easily achieving 4000+ RPMs upon throttle engagement. We thought shifter cables? Not sure because in neutral the engine responds. These items lead me to believe something to do with prop/drive - whatever is accepting the power provided by the engine. Could it be low drive fluid? Is there a way to check that while in the water? |
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| Author: | Flyer51 [ Sun Jun 09, 2019 2:46 pm ] |
| Post subject: | Re: Lost 10mph Volvo Penta 8.1L Gi |
Is this the original fuel pump that came with the boat? If so this is a known issue and there has been quite a bit written on the subject. If it is the fuel pump it can leave you stranded before long. Prop removal is relatively easy. When I first read your post I was thinking damaged prop. A simple visual inspection should help. Also be aware that a fouled hull can easily cost you 10 mph and made it difficult to get on plane. |
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| Author: | Raft61 [ Sun Jun 09, 2019 6:25 pm ] |
| Post subject: | Re: Lost 10mph Volvo Penta 8.1L Gi |
Absolutely a fouled hull could be the issue and props certainly need to be checked. You can’t check the transmission oil while in the water. Being a 2008 model, I assume you have a DPS or OS drive and not the XDP (composite) drive? The XDP’s were prone to problems particularly with 8.1 engines. |
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| Author: | TX H210SS [ Sun Jun 09, 2019 10:59 pm ] |
| Post subject: | Re: Lost 10mph Volvo Penta 8.1L Gi |
How is low speed to rpm ratio...if going 30 at 3k before, is it the same. If you are getting higher rpm at specific speed that suggest you may have prop hub or related issue if hull condition is same. Other possibility as I had was the filter at the fuel regulator valve which is mounted on fuel rail along top of intake manifold. They had a secret notice this filter should be removed and replaced with stainless washer insert which takes 2 minutes and pair of needle nose pliers. Mine was clogged which prevent sufficient fuel flow. Of course reason was the paint debris from interior of fuel pump which went out shortly afterward and needed replaced...that was a 650 part cost but it would whine and was obvious fuel pump |
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| Author: | alanderson74 [ Mon Jun 10, 2019 9:12 am ] |
| Post subject: | Re: Lost 10mph Volvo Penta 8.1L Gi |
Thank you for your responses - I'd assume it is the original fuel pump - although the boat has had 3 owners so I not certain about that. The fuel pump replacements I looked at yesterday were in the $1500 range, although researching was difficult with spotty data connectivity out there - are they really that expensive?? A helpful slip neighbor poured rubbing alcohol in the fuel filter to see if it could possibly be clogged - planing was better, still slow but have new VOLVO fuel filters on the way. This weekend I'll have the hubby check the filter at the fuel regulator - do you happen to have a part number so I can order a stainless washer replacement? I have the DPS-A 1.78 drive... Electric trim is working. |
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| Author: | alanderson74 [ Mon Jun 10, 2019 12:36 pm ] |
| Post subject: | Re: Lost 10mph Volvo Penta 8.1L Gi |
Would you mind pointing us in the direction of where the filter is at the fuel regulator valve in this exploded diagram? Is the filter requiring the stainless washer insert part# 16 in the diagram? https://www.marinepartseurope.com/en/volvo-penta-explodedview-7747720-23-22095.aspx 
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| Author: | zims1993 [ Mon Jun 10, 2019 1:18 pm ] |
| Post subject: | Re: Lost 10mph Volvo Penta 8.1L Gi |
The fuel pump assy's can be had for around $250. Check our this page as Troy is a very great person to work with www.mancavemechanic.com |
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| Author: | alanderson74 [ Mon Jun 10, 2019 6:36 pm ] |
| Post subject: | Re: Lost 10mph Volvo Penta 8.1L Gi |
Speak of the devil - I've been emailing him about this today lol |
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| Author: | Misterfu02 [ Mon Jun 10, 2019 9:33 pm ] |
| Post subject: | Re: Lost 10mph Volvo Penta 8.1L Gi |
You said you had a mooring line caught in the prop? You probably spun a hub. Not sure about the DP but on SX's you can mark the hub and prop with a paint pen or something and see if it spins. Highly doubt it's the fuel pump if it's running good. It'll make a screeching sound and the boat will run like crap if it's the fuel pump. |
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