454 mag possible bad head gasket need some advice

[cableguy1979]

Ok so I bought a 1996 crownline with a 454 mag from a friend. I know the boat but I don't know what's wrong. First the boat was left open to the weather and the boat filled with rain water. It got in the fuel tank and after it was drain it was attempted to start. There was enough water in the boat to be up to the engine. The engine had water in the oil which I assume came in from the intake and past the rings, water in the fuel rail and water in the outdrive from sitting filled up so long. Guy swears it ran great no problems until it filled up. I rebuilt the VST and purged as much of the water out of the fuel system as possible with compressed air while having the shrader valve open and pressurizing the fuel system and turning over the motor. New filters, new oil and new plugs. Boat fires up and runs but idles around 1200 to 1500 depending. When I first start it it runs around 1200 but after I rev it it idles around 1500 and wont settle down back to 1200. I let it run for about 15 minutes twice. I pulled all the plugs and number #8 has water on it. I start the boat with the plug out and let it expel any water twice but still get water on the plug. I dont know if there is more water in the fuel rail but I think one cylinder with water on it is doubtful especially after 15 minutes of runtime. So i feel i need to start looking for a busted head gasket or can a exhaust riser gasket cause this? If i do a leak down test how could i tell? Seems to me if its the head gasket it will leak down no matter what. If the exhaust riser can let water in then should not leak down on compression stroke but when the exhaust valve is open it will let water in? I still don't see water in the oil as of yet but the condensation on the plug doesnt say there is enough water from that cylinder to have any milky oil yet.

Any clue what is causing the engine to idle so high? I hear a ticking lifter but not a cause for high idle. TPS, idle air? What do I test first?

Any help is greatly appreciated

 

[cableguy1979]

I bypassed the fuel tank by taking the fuel line off the tank and sticking it in a can of gas. This shouldn't cause a high idle right? I have the sending unit out of the tank as well but I read something about vacuum in the fuel system causing a problem like this. If this is possible can someone explain to me how?

 

[tpenfield]

OK, those boats that you get from 'friends' can be a challenge. Regardless, here are my thoughts . . .

Definitely do a compression test and a cylinder leak test and take specific #'s and information as to where you hear leakage from the cylinders.

Water in the cylinders of a running engine is never a good thing. If you were getting leakage from the exhaust manifold/risers, then it would most likely show up on the middle cylinders (3,5,4,6). The fact that you are seeing water in #8, may mean something different. Are you in an area where the winter temperatures drop below freezing? If so, have you considered that the engine was not winterized and may have a cracked head/block, etc?

As far as the high idle . . . Since you have a VST pump, I assume we are talking about the 454 Mag MPI engine (right?). A small air leak around the intake plenum will give you a high idle. So, check all of the hose connections to the plenum and the gaskets where the plenum mates to the intake manifold.

I would also pressure test the cooling system to check for engine block cracks. You'll have to block off the water intake and output hoses, but it may be worth your time to do so, given the TLC that the boat has not received.

As far as the boat, if it filled up with water that much, as you described, anticipate that the structure is now full of water, particularly the fuel tank bay. The boat may have a shortened life due to rotting of the structure. The fuel tank may fail due to corrosion. All these are bad things. So, take some time to check the fuel tank bay and other areas of the structure for water retention, etc.

 

[Bt Doctur]

Being a fuel injected motor the throttle is operated by a throttle position sensor . An electrical rheostat that varies the voltage signal going to the computer that tells the computer what to do.If the motor was that far under water it drowned and all wiring is suspect, all electrical connections and all electrical components