Mercruiser 5.0L MPI Not Starting, I was driving the boat at a slow pace and it slowly stalled/stopped

[Robertse]

Dear All, Rob from Australia. I have a SeaRay 270 Sundance with Mercruiser 5.0L MPI which is Not Starting.

I was driving the boat at a slow pace and it slowly stalled/stopped and I can’t get started again. It turns over but will not start. So I did the following:

• I checked and have spark (orange spark). Opened the distributor cap and cleaned the points under the cap with a wire brush. Also I just replaced the spark plugs with new plugs, as the old spark plugs were black as it may have been running too lean / rich. There is no water in the engine, it is dry.
• I have taken out the thermostat some months ago as it was running slightly hot in the past (at one stage it got up to 190-200 and I turned off the engine to cool it down). The thermostat is new and works, I will put it back in. This may be the reason it was running too lean / rich.
• Connected Fuel/Gas Pressure Gauge and cranked he engine, it had 40 Psi and after about 30 minutes It will slowly go down to 25 PSI. In the last 4 months I replaced both fuel pumps (low pressure and high pressure water cooled pumps).
• I did a compression test with the following results. Cylinder 1=150, Cylinder 2 =15 (Spark Plug was melted and bent, see the attached photo, this is new, never seen this before). Cylinder 3 = 115 and Cylinder 4 = 115, Cylinder 5=60, Cylinder 6 =150, Cylinder 7 = 100 and Cylinder 8 = 115.I know the compress is low, but it is the same results as it was 4 months ago, I have been driving the boat like this for the last 4 months and was going to take the heads off this winter, inspect and recondition them. However what is new issue is Cylinder 2 =15 (Spark Plug was melted and bent, see the attached photo, this is new, never seen this before).

I am not sure what else to check to get it going, or should I take off the heads now. Thankyou in advance.

 

[alldodge]

Key ON fuel pressure goes to 40 psi and with key left on or turned OFF it slowly goes to 25. If this is happening then the fuel pressure is fine

Does it ever try to start or nothing but just cranking?

With compression only good on 2 cylinders, it would be time to get into the motor and find out if it needs a rebuild or just the heads

I would try replacing the distributor cap because they can look great but still be bad

Pour contents of the fuel filter into a clear container to see if there is anything but clean gas

Need a scanner to see if there are any codes

 

[Scott Danforth]

with compression that low, I would be doing a leakdown test ASAP

 

[cyclops222]

Burned / melted sparkplugs ? Low compression ? Valves sticking open. Loads of black carbon stuck inside of cylinders. Orange spark.
Run it. Until it stops.
Done

 

[Bondo]

Cylinder 2 =15 (Spark Plug was melted and bent, see the attached photo, this is new, never seen this before).

Ayuh,....... That happens, usually from detonation,.....
I'm guessin' that piston looks about like that spark plug,....

 

[ESGWheel]

I am a little perplexed. Here is why > a motor needs 3 basic things to run: fuel, spark and compression. You have two of the three. And short of doing a rebuild of the heads or, more likely, the entire engine anything else is fruitless. That is No. 1 priority IMO and that you continued to run it knowing low compression these cylinders for 4 months prior to discovering the issue with no. 2 probably resulted in more damage. It was best to stop 4 months ago.

The idea of “running a boat motor to fail” is dangerous and never should be done. Note: ‘Run to Fail’ is a term that is used in some industries to capture the idea of no maintenance on their equipment until it simply does not run anymore. Then fix it. This is what companies do when cash poor. When boating your life depends on the integrity of the hull and the proper running of the engine amongst items, like seamanship.

So maybe I should say I am shocked anyone would run this way or think ok to keep running until failure.

More: your blacked up plugs, indicating a rich (not lean) condition, were a telltale that something was going wrong. And the melted plug indicates an extreme lean / detonation condition. Thus, post your engine rebuild you probably still have issues that, left unchecked, may put you back in the same condition you find yourself now.

 

[Buster53]

I used to have a boat with a Merc 5.0 and was having starting, idling issues. Replaced the idle control valve and all was good. About a $40 part. Check it out on YouTube videos.

 

[Bt Doctur]

show a pic of ALL the plugs, the one you show has severe detonation damage and the piston probably looks worse

 

[Robertse]

Key ON fuel pressure goes to 40 psi and with key left on or turned OFF it slowly goes to 25. If this is happening then the fuel pressure is fine

Does it ever try to start or nothing but just cranking?

With compression only good on 2 cylinders, it would be time to get into the motor and find out if it needs a rebuild or just the heads

I would try replacing the distributor cap because they can look great but still be bad

Pour contents of the fuel filter into a clear container to see if there is anything but clean gas

Need a scanner to see if there are any codes

show a pic of ALL the plugs, the one you show has severe detonation damage and the piston probably looks worse

Key ON fuel pressure goes to 40 psi and with key left on or turned OFF it slowly goes to 25. If this is happening then the fuel pressure is fine

Does it ever try to start or nothing but just cranking?

With compression only good on 2 cylinders, it would be time to get into the motor and find out if it needs a rebuild or just the heads

I would try replacing the distributor cap because they can look great but still be bad

Pour contents of the fuel filter into a clear container to see if there is anything but clean gas

Need a scanner to see if there are any code

Thankyou confirming the Fuel/Gas Pressure is fine. It did start once for about 40 seconds. I will replace Distributor Cap, I will check the Fuel Filter as you stated. I take the Heads offs, inspect, pressure test and recond. I will inspect the Pistons, Bore, Cylinder Walls as see if I need to pull out the block and see if I need to install new pistons and rings. When I first got this boat last year, almost nothing worked (it was sitting in the water at stand still for 4 years). I had to replace or service, Alternator, Starter Motor, Fuel Pumps, IAC, Belt, Thermostat. Risers, Exhaust Manifolds, Impeller and Impeller/water pump housing ( it had a hole in it and leaking water) The Bravo 3 Leg/Gears Box was a nightmare (the worst state that I ever seen), I pulled it apart and replaced many components, welded and patch many holes casting, new bellows, gimbal bearing, gear cable, Hydraulic Lines. Windlass, fresh water pump, stereo..... And when I put it in back in the water 4 months ago, the transom gimbal ring snapped and cracked ripped the new bellows I just installed. Then I had take the boat out of the water to do an emergency replacements and replace the Transom Ring. This boat was my nightmare and never again will a buy a boat in this bad condition.... So to get the motor running for a few months (so the kids can have some fun) was a relief and blessing . I tried to run it to see if the values become unstuck, if not I knew I had to attend to the heads. Now I am hoping the cylinders are fine.

 

[Robertse]

I am a little perplexed. Here is why > a motor needs 3 basic things to run: fuel, spark and compression. You have two of the three. And short of doing a rebuild of the heads or, more likely, the entire engine anything else is fruitless. That is No. 1 priority IMO and that you continued to run it knowing low compression these cylinders for 4 months prior to discovering the issue with no. 2 probably resulted in more damage. It was best to stop 4 months ago.

The idea of “running a boat motor to fail” is dangerous and never should be done. Note: ‘Run to Fail’ is a term that is used in some industries to capture the idea of no maintenance on their equipment until it simply does not run anymore. Then fix it. This is what companies do when cash poor. When boating your life depends on the integrity of the hull and the proper running of the engine amongst items, like seamanship.

So maybe I should say I am shocked anyone would run this way or think ok to keep running until failure.

More: your blacked up plugs, indicating a rich (not lean) condition, were a telltale that something was going wrong. And the melted plug indicates an extreme lean / detonation condition. Thus, post your engine rebuild you probably still have issues that, left unchecked, may put you back in the same condition you find yourself now.

Thankyou for your reply and valued input, much appreciated . . When I first got this boat last year, almost nothing worked (it was sitting in the water at stand still for 4 years). I had to replace or service, Alternator, Starter Motor, Fuel Pumps, IAC, Belt, Thermostat. Risers, Exhaust Manifolds, Impeller and Impeller/water pump housing ( it had a hole in it and leaking water) The Bravo 3 Leg/Gears Box was a nightmare (the worst state that I ever seen), I pulled it apart and replaced many components, welded and patch many holes in the casting, new bellows, gimbal bearing, gear cable, Hydraulic Lines. Windlass, fresh water pump, stereo..... And when I put it in back in the water 4 months ago, the transom gimbal ring snapped and cracked ripped the new bellows which I just installed. Then I had take the boat out of the water to do an emergency replacements and replace the Transom Ring and bellows. This boat was my nightmare and never again will a buy a boat in this bad condition....I was hopping the value springs was just stuck and will inprove if the engine runs for a while. I should of did another compession test after using it for a couple of days, 4 months ago. Anyway to get the motor running for a few months (so the kids can have some fun in our summer was rewarding) it was a relief and blessing . I knew I had to attend to the heads. Now I am hoping the cylinders are fine...Thankyou again.. Peace

 

[ESGWheel]

Thankyou again.. Peace

Thanks for the soft reply to my sharp post. I read thoroughly your intentions as well as the significant tribulations you have undergone with a lot of empathy. And I re-read all prior to my post and realized I was merging your 4 months of a known issue with a recommendation to ‘run to fail’. I now understand that your intention was NOT to run to fail but my grave concern over such a tactic was already in full swing. The concept or suggestion to go boating until a failure (of engine, hull or another key element necessary for survival) is simply abhorrent in my book and I reacted strongly.

Make no mistake, this is learned concern. In my youth, with my 65 Goat (Pontiac GTO) I was incredibly reckless as the tire marks in a tunnel between Alameda and Oakland (California) can attest to. That I survived past the age of 16 is still a mystery to me.

I joined the US Navy (submarines) and the lessons of the lost USS Scorpion were drilled into us. Never again. To say the least I gained a strong perspective of safety and the merits therein and have lived my life with a value of safety ever since.

And interestingly, I have had the pleasure of visiting Down Under. Was in 1981 (I think) and our submarine pulled into Fremantle – a little south of Perth. Typical of the time, we had a shore phone (twisted pair) as part of the port logistics except in this case they delivered two phone lines. Two? Turns out one was dedicated to “Dial A Sailor” which, to our surprise, was being advertised full week prior to our arrival (submarine movements are supposed to be secret!). We had to station a dedicated watch with a flip chart to keep track of all the phone calls we were getting! I also remember two other uniquely Down Under attributes: Road Trains and that the memory of WW2 still prevails > I do not recall ever having to buy a beer as soon as I opened my Yank mouth and folks figured out I (we) were off the US submarine currently docked in Fremantle. Great times!

Keep posting, learning, do good and be safe. Cheers!