RE: Issues with Mercruiser 5.0 LX 4 Barrel Carb

[BusinessConnected]

Good Evening from Melbourne, Australia.
I've got a Bayliner Ciera 2355 which is new to me this Summer.
(Mercruiser LX 5.0 4 Barrel Carb with Alpha One Gen 2 Leg)

Initially ran fine but managed to seem to have some Foam Stuck in the Propeller after running for 3 hours on a Local Freshwater Lake (Lake Eildon) and wouldn't REV Past 2500rpm.

Subsequently I diagnosed the issue as a dodgy Fuel Mechnical Fuel Pump.

After an afternoon of Swearing I managed to replace that Pump and Engine was Idling really well etc.

Took Boat out on Sunday, Started First Go without Issue. Struggled to get on the Plane.. Felt like Full Throttle was only 3000rpm or so.

After I managed to get on the Plane throttle seemed to come good, would Rev to 4000rpm which I would back off down to 3500 or so.

Anyhow after about 10 minutes of that I heard a distinct change in Engine Note.. a sort of whirring.. subsequently shut down engine and could see signs of overheating. Bit of "Crackling" coming from the Block etc.

Got towed back to Boat Ramp, after 45 minutes of Towing the Boat would Start and Idle but not shift into any gears etc.

Anyhow have managed to get the Boat Home again now and have done some troubleshooting

• If I don't start the Engine for 24 hours or so... It will initially start and idle.. somewhat poorly but will run.
• After Running it won't start again... makes sounds as if its almost turning over but doesn't go any further.
• Have Removed Water Lines from the Exhaust Manifold and Riser on Both Sides and Water will flow through these correctly.
• When The Engine Started this Morning it ejected a sort of Carbon Gunk Build Up that sort of flaked apart in my hands,
• I can't see any evidence of Impeller on Alpha Working... I believe Leg is only around 3 years old so I have ordered a Service Kit for that.
• I have disconnected Main Fuel LIne to Carb and confirmed that it is delivering Fuel when Cranking, and I've also replaced Fuel Filter again.

Any other obvious troubleshooting steps at this point in time?

 

[stresspoint]

welcome from fellow Aussie , ( Perth ) ,
i would start by removing the outdrive , check the pump impeller and then for obstructions in the water passages / hoses to the motor.

it sounds as if you may have overheated the motor ? is there any sign of water in the oil , if not a head gasket may have blown between cylinders hence rough idle , a compression test will tell the story .

 

[BusinessConnected]

welcome from fellow Aussie , ( Perth ) ,
i would start by removing the outdrive , check the pump impeller and then for obstructions in the water passages / hoses to the motor.

it sounds as if you may have overheated the motor ? is there any sign of water in the oil , if not a head gasket may have blown between cylinders hence rough idle , a compression test will tell the story .

I definitely believe there is an issue with the Impeller.. I've order that from marineparts ex Brisbane and it;s on its way down for a changeover.
I've tested the flow around the Engine with the Water Pump Hose Removed and Running a Garden House into the Disconnected Hose... Results in Water Flowing around the Block etc... So it doesn't necessarily appear that any Water Passages are blocked per se..

I'm intending to replace both the Engine Water Pump and Impeller when they arrive.

 

[Scott Danforth]

any new to you boat needs to have the raw water pump (whole pump) changed, the u-joints inspected and the gimbal bearing and bellows changed.

the engine circulating pump hardly ever goes bad

if this is a saltwater boat over 7 years old, time to inspect the exhaust manifolds and elbows as well.

 

[BusinessConnected]

Boat has been Fresh Water from what I have been advised... Hasn't had a lot of outings in last 4-5 years. I've been advised the Leg was replaced under Insurance Claim 2 Years ago.

 

[Scott Danforth]

Boat has been Fresh Water from what I have been advised... Hasn't had a lot of outings in last 4-5 years. I've been advised the Leg was replaced under Insurance Claim 2 Years ago.

every year the maintenance schedule requires the drive to be pulled, the alignment checked and the gimbal bearing and u-joints inspected. doesnt matter if the boat is new or 2 million years old.

additionally, since the boat sat is exactly why you need to do all the PMs the prior owner didnt do. like oil changes and impeller changes.

make sure to find all the missing pieces of your old impeller.

 

[stresspoint]

i miss lake Eildon, it must be pretty busy up there since the Murray got floods.
that said , do that compression test to address that rough running.
the 5.0 is a robust motor but the head gaskets are a weak point when they get heated from lack of water flow.

? did any smoke come from the riser elbow rubbers.

 

[stresspoint]

can you please explain this occurrence in more detail. >>>> the Boat would Start and Idle but not shift into any gears etc.

 

[BusinessConnected]

So when the Boat overheated, I could see Smoke Rising from the General Surrounds on the Engine... their didn't seem to be any particular place it was coming from.. just seemed like Burning Oil type Smoke from everywhere.

When I first attempt to Start the Boat after 24 hours or so... it will Turn over and run at idle etc... When I attempt to shift in Forward or Reverse it will immediately Stall/Shut Off.

After this point I'm unable to Start the Motor again... it will crank and you'll get around 1-2 seconds of apparent running but nothing else.

 

[Scott Danforth]

So when the Boat overheated, I could see Smoke Rising from the General Surrounds on the Engine... their didn't seem to be any particular place it was coming from.. just seemed like Burning Oil type Smoke from everywhere.

When I first attempt to Start the Boat after 24 hours or so... it will Turn over and run at idle etc... When I attempt to shift in Forward or Reverse it will immediately Stall/Shut Off.

After this point I'm unable to Start the Motor again... it will crank and you'll get around 1-2 seconds of apparent running but nothing else.

pull your drive, then try

take a compression reading. a good motor is 150 psi in all 8 cylinders. a worn motor is 125psi or below

shove a garden hose in the hole in the bellhousing for cooling water

 

[crazy charlie]

So when the Boat overheated, I could see Smoke Rising from the General Surrounds on the Engine... their didn't seem to be any particular place it was coming from.. just seemed like Burning Oil type Smoke from everywhere.

When I first attempt to Start the Boat after 24 hours or so... it will Turn over and run at idle etc... When I attempt to shift in Forward or Reverse it will immediately Stall/Shut Off.

After this point I'm unable to Start the Motor again... it will crank and you'll get around 1-2 seconds of apparent running but nothing else.

Pull the oil fill cap on the valve cover and look for water in oil foam before you go any further.Charlie

 

[stresspoint]

So when the Boat overheated, I could see Smoke Rising from the General Surrounds on the Engine... their didn't seem to be any particular place it was coming from.. just seemed like Burning Oil type Smoke from everywhere.

When I first attempt to Start the Boat after 24 hours or so... it will Turn over and run at idle etc... When I attempt to shift in Forward or Reverse it will immediately Stall/Shut Off.

After this point I'm unable to Start the Motor again... it will crank and you'll get around 1-2 seconds of apparent running but nothing else.

it sounds like the oil pressure switch is stopping the motor from starting , however , can you try again with the " shift interrupt" switch disconnected (to rule that out) and report back.

 

[BusinessConnected]

it sounds like the oil pressure switch is stopping the motor from starting , however , can you try again with the " shift interrupt" switch disconnected (to rule that out) and report back.

Thanks for all your replies.
I'm just waiting on a number of parts etc to be delivered including my Compression Test Gear (My Old Set was Broken in a Move).

I will post a reply once I have an update.

 

[Scott06]

After this point I'm unable to Start the Motor again... it will crank and you'll get around 1-2 seconds of apparent running but nothing else.

based on this symptom i would cycle the man overboard kill switch on and off. If it is cut off, engine will just catch during cranking but have no spark in run… crank , just catch, then die

 

[BusinessConnected]

So I've had the Right Side of the Engine off today...
Flappers are completely gone.. even the housing that Holds them in place has melted and damaged.
Exhaust Manifold itself looks ok, but risers have a significant crack on them.

At this point I'll be moving on to Compression Testing... but thought I'd show some progress.


I'll be replaced the Manifold/Riser on both sides.
I assume I probably need to drop the Alpha Leg from rear of boat to be able to ensure all the contaminated Flapper Bits etc are gone?

 

[stresspoint]

So I've had the Right Side of the Engine off today...
Flappers are completely gone.. even the housing that Holds them in place has melted and damaged.
Exhaust Manifold itself looks ok, but risers have a significant crack on them.

At this point I'll be moving on to Compression Testing... but thought I'd show some progress.


I'll be replaced the Manifold/Riser on both sides.
I assume I probably need to drop the Alpha Leg from rear of boat to be able to ensure all the contaminated Flapper Bits etc are gone?

you will need to remove the bull horn as well to check for debris.

 

[BusinessConnected]

Hello Guys:
Todays Updates... I've had an inspection camera down both sides of the Exhaust Y Piece/Bullhorn and they appear clear.

I've flushed the Bull Horn with Water and Flow is good out the rear of the Alpha Drive Unit. Not saying this is definitive, but its the best I can do at Home currently.

Compression Test Results however are a little bit more disappointing.
Right Side (Front Front of Boat)
Cylinder 1 : 130PSI
Cylinder 3: 50PSI
Cylinder 5: 120PSI
Cylinder 7: 120PSI
Left Side (From Front of Boat)
Cylinder 2: 110PSI
Cylinder 4: 110PSI
Cylinder 6: 115PSI
Cylinder 8 :120PSI

Obviously they are a little low to begin with, however Cylinder 3 is the big concern.

Just in terms of Testing Method to confirm I did the Compression Test with
- All Spark Plugs Removed
- Ignition Leads Isolated in Seperate Plastic Zip Lock Bags Cable Tied
- Carb etc was still connected so Some Fuel was exiting Exhaust Manifolds at Cylinders 7 & 8

(As Both Exhaust Manifolds/Risers are currently removed)

 

[stresspoint]

you need to figure out why the engine got that hot and stayed hot long enough to smoke the motor component's so badly..? was the foam wrapped around the front of the lower gearbox blocking the water intake holes.

i am surprised there is not water in the oil from that overheat on a SB chev, so in a way you have dodged a built and the motor is rebuildable without the need for extensive crank work.

 

[BusinessConnected]

you need to figure out why the engine got that hot and stayed hot long enough to smoke the motor component's so badly..? was the foam wrapped around the front of the lower gearbox blocking the water intake holes.

i am surprised there is not water in the oil from that overheat on a SB chev, so in a way you have dodged a built and the motor is rebuildable without the need for extensive crank work.

Stresspoint:
I believe there is an issue with the Impeller on the Leg because there isn't any flow.. We will be rebuilding that tomorrow..

Can't see any signs of water that I can see..

 

[Scott Danforth]

Cranking psi is listed at 150 psi in the factory manual. Your compression numbers have a motor that will run, barely, however be down on power. I would pull the motor and plan on replacing. A 5.7 will bolt right in if you choose to upgrade