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

R

Robertse

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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.
 

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Robertse said:
or should I take off the heads now.
Click to expand...
Ayuh,...... You might as well look to see how bad it is,.....
My guess is you need a new long block motor,.....

Yer thread is getting good traction over at iboats, 'n the verdict is not good,...
 
Looking at the plug and your fuel pressures. I will assume you were running lean and or too much timing.
Once you pull the head I am sure you will find piston damage. Prob melted piston to the 1st ring. Also, you might find some burned exhaust valves,
This may explain the overheat problem as well.
Replace the engine, drain and refill the fuel tank, and reset ign timing.
 
eclipseguy said:
Looking at the plug and your fuel pressures. I will assume you were running lean and or too much timing.
Once you pull the head I am sure you will find piston damage. Prob melted piston to the 1st ring. Also, you might find some burned exhaust valves,
This may explain the overheat problem as well.
Replace the engine, drain and refill the fuel tank, and reset ign timing.
Click to expand...
Thankyou for your reply. It only partly overheaded once reaching 190-200 and I quickly turn off the engine. I am hoping the pistion and wall/bore is not damaged. I have replaced the pistons and rings in these engines before, it is a pain pulling out the engine block and puting the engine back in the boat.
 
Robertse said:
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.
Click to expand...
Sorry for the late update. I put this project aside and re-started it this again the last 2 days. I pulled off both heads. I place the engine at Top Deah Centre before pulling the heads off. Before I pulled the heads off 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 discovered that piston 2; had a hole in it and slightly crack as the valve snapped and pieced a hole in the cylinder. I have attached photos (the photos was taken before I clean the bore and piston). Because it is a pain to put out the engine block, my aim is to tig weld the hole / crack while the cylinder 2 is in the block?

Piston 5, the valves are rusted close, and there is some minor pivoting in the cylinder wall which I will try to hone out. I am going to service the heads. It check that there is no play or knocking in the cylinder , The head gaskets was fine, not breaks, holes or damage. So my concern there is evidence of rust / water in Cylinders 2 and 5. How did water get into those specific cylinders while the head gasket was intact. What cause valve to break on cylinder # 2? Thanks in advance.
1763675999403.png
1763676044732.png
 
That also looks like there was water in that cyl for a while. Welding up that hole in the piston isn’t going to fix it. The cyl walls appear quite rusted. I think the block has to come out….
 
Water in cyl ….looks like there’s a hole in the cyl head…heads could be rusted due to salt water use….
 
Robertse said:
Sorry for the late update. I put this project aside and re-started it this again the last 2 days. I pulled off both heads. I place the engine at Top Deah Centre before pulling the heads off. Before I pulled the heads off 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 andThanks Cylinder 8 = 115.

I discovered that piston 2; had a hole in it and slightly crack as the valve snapped and pieced a hole in the cylinder. I have attached photos (the photos was taken before I clean the bore and piston). Because it is a pain to put out the engine block, my aim is to tig weld the hole / crack while the cylinder 2 is in the block?

Piston 5, the valves are rusted close, and there is some minor pivoting in the cylinder wall which I will try to hone out. I am going to service the heads. It check that there is no play or knocking in the cylinder , The head gaskets was fine, not breaks, holes or damage. So my concern there is evidence of rust / water in Cylinders 2 and 5. How did water get into those specific cylinders while the head gasket was intact. What cause valve to break on cylinder # 2? Thanks in advance.
Click to expand...

AllDodge said:
Most likely a clogged/bad injector and causing the cylinder to run lean, which in turn causes detonation
Click to expand...
AllDodge said:
Most likely a clogged/bad injector and causing the cylinder to run lean, which in turn causes detonation
Click to expand...
Thanks for the reply. Ok I will pull out and check the injectors, I run it without thermostat for a while do you think, that caused it to run lean
 
Robertse said:
Sorry for the late update. I put this project aside and re-started it this again the last 2 days. I pulled off both heads. I place the engine at Top Deah Centre before pulling the heads off. Before I pulled the heads off 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 discovered that piston 2; had a hole in it and slightly crack as the valve snapped and pieced a hole in the cylinder. I have attached photos (the photos was taken before I clean the bore and piston). Because it is a pain to put out the engine block, my aim is to tig weld the hole / crack while the cylinder 2 is in the block?

Piston 5, the valves are rusted close, and there is some minor pivoting in the cylinder wall which I will try to hone out. I am going to service the heads. It check that there is no play or knocking in the cylinder , The head gaskets was fine, not breaks, holes or damage. So my concern there is evidence of rust / water in Cylinders 2 and 5. How did water get into those specific cylinders while the head gasket was intact. What cause valve to break on cylinder # 2? Thanks in advance.View attachment 36513View attachment 36514
Click to expand...
1763700059625.png
 
louc said:
Water in cyl ….looks like there’s a hole in the cyl head…heads could be rusted due to salt water use….
Click to expand...
Thanks for the reply, The water jackets in the head was completely blocked, I had to clear them up, is there anyway I can I can check pressure test the head for internal cracks?
 
The water could have come in from the exhaust system which rusts like the inside of the engine. In salt water they should be replaced after about 7 years of use. If the heads are totally clogged with rust I’d take them to a machine shop & ask if they can be saved. The block, well from what I can see in the pics it needs to come out….
 
Sorry to say it looks like an end of life salt water unit. My experience in the salt had taught me that raw water cooled cast iron engines need consistent maintenance and at about 15 years the cyl heads may be close to rusting through, the block can last longer but if the exhaust isn’t replaced when needed, you get salt water in a few cyls, then valves start sticking and cyl walls start rusting. If replacing an engine in that environment I’d always suggest adding at least a half closed cooling system and with Merc’s upgrade to their dry joint exhaust.
In my case I had an overheat and about 3 seasons later I had to replace the head gaskets & found I had to replace the heads as well (cracked, and cooling passages were getting eroded). Water in a cylinder. But it turned out to be a blessing in disguise because if that hadn’t forced me to take it apart the original heads probably would have rusted through and hydrolocked the engine…In fact now I’m going out to the boat to inspect the inside of the elbows to see if they and the manifolds need replacing…
 
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