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Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 16114
Experience:  Degree in Marine Technology. Gas and diesel marine mechanic.
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Jason. I'm Steve. I have a 2008 mercruiser 5.0 mpi that

Customer Question

Hello Jason. I'm Steve. I have a 2008 mercruiser 5.0 mpi that runs good at low speed, but when applying throttle will not speed up quickly and smells rich. Starts okay. I have heard distributed cap could be bad. Water pump went out last week and engine got a little hot, but not too bad.
Submitted: 2 years ago.
Category: Boat
Expert:  Jason replied 2 years ago.
Hi Steve my name is ***** ***** I will be helping you today. Has compression and fuel pressure been checked yet? If not, those are the first checks.
Customer: replied 2 years ago.
No to both the boat was running fine, and it has not had plugs in a while so I thought I would start there. What should compression and fuel pressure be.
Expert:  Jason replied 2 years ago.
Compression needs to be 100 psi minimum, and all cylinders should be within 15% of eachother. When the engine was new compression was 180+ psi. If the engine has low hours I would expect to see a reading in the 160 to 180 psi range. Fuel pressure is 43 psi.
Expert:  Jason replied 2 years ago.
Was the engine running perfectly before it got hot last week, or did it still have running issues before that?
Customer: replied 2 years ago.
It ran great prior to getting hot.
Expert:  Jason replied 2 years ago.
If it ran great prior to it getting hot there is a good chance a head gasket let go on you.
Customer: replied 2 years ago.
Thanks. Not very encouraging, but I will start checking it out.
Expert:  Jason replied 2 years ago.
When an engine "smells" rich there are really only 4 conditions that an cause that.1. Low compression - When compression gets to low the cylinder can not burn all of the gas that enters that cylinder. And it can't burn it because it can't compress it. Gas has to be compressed to explode, and create power. But when it's not compression it will just burn no differently than if you spilled some gas on the ground and lit it on fire. 2. High fuel pressure - If there is more fuel entering the engine than the engine is calibrated for, again that will cause the cylinder not to be able to burn it all. 3. And EFI sensor issue - There are all sorts of sensors on the engine that read pressures and temperatures. If a sensor is not reading correctly it will cause the engines computer to call for to much fuel, when the engine doesn't need it. A good example of that is the temperature sensor. A cold engine needs more fuel than a hot engine. And when the engine is cold the computer will injector more fuel. If the temp sensor is bad, and always reading cold, even though the engine is hot, the computer will be injecting the amount of fuel for a cold engine. 4. Lastly a stuck open thermostat. If the engine has a stuck open thermostat it will never get hot. And cold engines to run rich.
Expert:  Jason replied 2 years ago.
However, if you try to connect the dots and see if the problem you have now is related to the engine overheating. You can draw a direct line and connect an overheating engine with a blown head gasket. So if the two are related, that is where I would be looking first.
Expert:  Jason replied 2 years ago.
But if you go through the rest of the list, there is no direct connection between an overheating engine and numbers 2, 3 and 4 on my list. The only way #4 could be connected is if when the impeller was changed the thermostat was removed and there was no thermostat in it.
Expert:  Jason replied 2 years ago.
Does that all make sense?
Expert:  Jason replied 2 years ago.
Did you have any further questions on this, or was there anything else I could help you with?