2007 wakesetter cylinder 8 misfire under load

[Wrex0215]

I figured I'd get some other opinions seeing as I've been getting my butt kicked by this thing for over a year now. 2007 21 VLX with a monsoon 340 with 615 hours on it. Boat spits the service required message and shortly after that the engine fault, cylinder 8 misfire- mechanical system not responding properly code rolls in and puts the boat into limp mode. Only happens when its working hard under load (ballasts full, surfing with at least 5-6 people on board). The kicker is sometimes it will run perfect for a whole day and then the next day no dice. I have noticed when its about to act up the RPMs starts slowly dropping off not allowing the boat to keep up with whatever speed the cruise control is at before it drops right down into limp mode.

The person who owned the boat before me took it to the local Malibu dealer twice for the problem and they couldn't solve it however it was winter so they couldn't lake test it. The plugs, wires, cap, rotor and fuel filter(x2) have been replaced. I put a new injector in it and it ran great for a day and half after which hasn't happened since. I've read that a bent shaft or damaged prop could throw off the knock sensors enough to throw the code but those have since been replaced. Compression in all the cylinders are good and close.

I've heard the gen 2 in tank fuel pumps are only rated for 500 hours so upgrading to a gen 3 fuel pump may be next on my list although i'm hesitant because the current fuel pump still pushes 45psi at the fuel rail and it wouldn't make sense as to why it runs good sometimes. Not to mention they aint cheap. I currently have the boat in a million pieces seeing as its not surfing season in Canada for another couple months. I have the current fuel pump sitting on the bench, the screens on the bottom look clean and the inside of the tank also isnt bad. A couple specs here and there but clean for the most part. I am planning on giving it a proper clean out when i get home from work in a week. 

Another thing i've heard about is the lower intake gaskets on the 5.7 vortecs failing and oil making its way into the intake. There was a small oil puddle on the intake plenum when i pulled it off but i've been told to expect that with these motors? I will prob end up doing these gaskets unless I'm missing something obvious. 

I know it could be a timing issue i just dont have a diacom to check cam angle and i thought that would have been something the dealer looked at the second time around at least. 

I'm also not closing the door to it being an electrical/voltage issue . The thing came fitted with 3 batteries, a pile of speakers and a sub. I cant remember what the battery terminals looked like last year but when i cleaned them up a couple weeks ago there was a fair amount of corrosion.

Sorry for the long write up! Any input would be greatly appreciated. 

 

 

[csleaver]

The fuel pressure seems low at 45 PSI compared to the recommended 55-62 PSI on the Indmar fuel pressure chart.  That could cause a misfire problem. 

You should also check the cam angle and make sure it is between 700-710 at 1200 RPM to prevent misfires.

[skurfer]

^What he said. When plugged into Diacomm, the cam angle should be 705  + or - 5 above 1,200 RPM's. Start there. 45 PSI isn't good enough but make sure you have a fluid filled or digital fuel pressure tester!

Other than that. Test all those batteries, sounds like a wiring nightmare.

 

[Wrex0215]

Thanks for the feedback! A wiring nightmare is an understatement.

New fuel pump is on the way if that doesn't solve it I'll be biting the bullet and ordering the diacom. 

[Wrex0215]

Figured I'd put out an update just in case anybody is having similar issues. I replaced the fuel pump and all 3 batteries and I'm now at 50 hours on the season code free!

Thanks again.