1996 Volvo Penta 5.8 FSI won’t run on water

Hello,

I will go ahead and apologize if this issue has been covered in a previous discussion. I am new to this site and I am still learning how to use it.

So, last fall I purchased a 1996 Chris Craft concept 21 with a Volvo 5.8 FSI powering it. My issue is that on the trailer hooked to muffs it runs perfect. The rpm’s bounce just a tad at idle but nothing major. When you put the boat in the water it idles and runs perfectly on smooth water but as soon as the boat starts to rock it coughs, sputters, sometimes backfires, and has a very hard time restarting. On a plane it runs perfectly in any type of water conditions. Also, it has a tough time getting on plane when it’s acting up(obviously) but if it can overcome the sputtering it clears up. Putting it in neutral and reving the engine to around 4K can sometimes fix the issue but not always.

Things I have replaced: distributor cap and button, spark plugs, fuel filter, and have cleaned the throttle body. I have filled the tank with a high level of sea foam and let it run for a while. I have not ran a compression, fuel or vacuum test yet but since it runs perfectly on the trailer I can’t see it being that.

If someone could help that would be great, Thanks!

I've got a 1995 5.8Fsi and I have not run into the situation your describing.

If it were my boat, and I knew it was fine on the trailer, and fine on smooth water, and fine on plane, and the only time it really acted up was when the boat was being bounced around...

First thing I'm checking is all connections and looking for a short. Make sure all connections are tight and wiggle every piece of harness and connector you can find.

Second thing I'm looking at is the fuel system. There is a fuel cooler on the back of these. The book calls it a "reservoir". There is a needle valve and float in it. I have heard that the float can get messed up and dump excess fuel into the motor. I can see that happening if your float is bad and you are in some chop. There is a rebuild kit out there for these. You might want to search this forum for "reservoir" and you can probably find my other posts about these and the part number to the rebuild kit. I have not experienced the problem yet, but I do have a rebuild kit on hand for when I finally do. These rebuild kits can be very rare and hard to come across.

Here is the part number for that rebuild kit. 3850374 Unfortunately, none on eBay right now, and that's the only place I know where you can find one. Someone has to list some NOS (New Old Stock) ones. These are long out of production.

Chris Rohde said:

Here is the part number for that rebuild kit. 3850374 Unfortunately, none on eBay right now, and that's the only place I know where you can find one. Someone has to list some NOS (New Old Stock) ones. These are long out of production.

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Thank you for the response and info. I will begin checking the things you listed and start looking for a rebuild kit of my own Incase that is the issue.

Will update on what I find out with it.

Thanks