Poor acceleration and no low end power

Therapydoc

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Bought a 2001 crownline lpx 225br. 350 mercruiser with captains call. The motor runs well without load. Revs and reaches rpm without difficulty. When in the water it hesitates and pops and coughs when trying to accelerate or when planed if I put it all the way down it just coughs and pops.

I did lose the an impeller first time out this year and it disintegrated. I flushed the system and thought I got it all out but maybe I didn't. What all should I check? I did change the fuel water separator and put seafoam in the gas.
 

Fun Times

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Hi, welcome to iboats!

Is the engine carbureted or fuel injected? Engine serial number handy?

You may need to check your fuel pressure as it could be low but not low enough to recognize it while in neutral gear. Revving a engine in neutral typically won't show signs of low power issues like you'd notice under load/on the water or on an propshaft dynamometer.

Also how hot did the engine get and for how long at that temp? Did it run good after the new impeller then run bad or just run bad right after the overheat situation?
 
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Therapydoc

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The boat overheated when lost the impeller and it killed itself. Had to be pulled back to the dock. Wasn't hot too long I don't think. I was pouring water on it to cool it back down. Only had it out 3 times. First time ran decent but not perfect but had less load also. Engine is 350 mpi so injected. Serial OM430790 How do I check the fuel pressure? Also the temp gauge I think is partly faulty bc it goes up to about 175 as usual but sometimes it kind bounces down then always settles back to 175. I never have water in boat when we are done for the day so don't think the block is cracked. Could there be parts of the old impeller lodged somewhere that's keeping me from getting back pressure?
 
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Fun Times

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The boat overheated when lost the impeller and it killed itself. Had to be pulled back to the dock. Wasn't hot too long I don't think. I was pouring water on it to cool it back down. Only had it out 3 times. First time ran decent but not perfect but had less load also. Engine is 350 mpi so injected. Serial OM430790 How do I check the fuel pressure? Also the temp gauge I think is partly faulty bc it goes up to about 175 as usual but sometimes it kind bounces down then always settles back to 175. I never have water in boat when we are done for the day so don't think the block is cracked. Could there be parts of the old impeller lodged somewhere that's keeping me from getting back pressure?
Sometimes the engine has a tendency to die when they get excessively hot at low RPM. With the popping, etc. going on 'Just wanted to bring up the possibility of internal engine damage such as head gaskets or valves should fuel pressure not be the issue.

To test fuel pressure, you'll need to find an EFI fuel pressure tester gauge at say an auto parts store that typically will read as high as 100 PSI and connect it the fuel schrader valve located at the end of the fuel rail on top of the engine. It's item number 6, https://www.perfprotech.com/mercury-...0?umodel=20473

Your fuel pressure should be right around the 30 psi +/-4.

Be sure to check the internal workings of your thermostat inside the thermostat housing as sometimes the rubber from the impeller will get stuck in the thermostat passageway causing fluctuations in engine temp.

Engine notes: MERCRUISER 350 MAG BRAVO MPI.
Parts guide, https://www.perfprotech.com/mercury-...g/umodel/20473
 
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Therapydoc

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Sometimes the engine has a tendency to die when they get excessively hot at low RPM. With the popping, etc. going on 'Just wanted to bring up the possibility of internal engine damage such as head gaskets or valves should fuel pressure not be the issue.

To test fuel pressure, you'll need to find an EFI fuel pressure tester gauge at say an auto parts store that typically will read as high as 100 PSI and connect it the fuel schrader valve located at the end of the fuel rail on top of the engine. It's item number 6, https://www.perfprotech.com/mercury...and-fuel-rails/assembly/2691/110?umodel=20473

Your fuel pressure should be right around the 30 psi +/-4.

Be sure to check the internal workings of your thermostat inside the thermostat housing as sometimes the rubber from the impeller will get stuck in the thermostat passageway causing fluctuations in engine temp.

Engine notes: MERCRUISER 350 MAG BRAVO MPI.
Parts guide, https://www.perfprotech.com/mercury-marine-parts-catalog/umodel/20473

To test do I test it at idle or with throttle? If fuel pressure is good, then do you think it is internal components of engine? I guess I was thinking engine was good because it runs decent with minimal load or most load in front of the boat and runs good when prop not engaged. Kinda starting to freak out now. Will be testing the pressure tomorrow.
 

Fun Times

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To test do I test it at idle or with throttle?
You'll want to check it at all aspects as possible... Key on - engine off, idle RPM at home on the garden hose, 1800 RPM, and up to full RPM as possible while on the lake when convenient especially since it's happening under load. Also there will be a black rubber vacuum line running down to the fuel pressure regulator located on the port side of the engine down under/behind the front motor mount close to the oil pan...With the fuel tester gauge connected and engine running, disconnect the vacuum line to see if the fuel pressure goes up 3 - 5 psi indicating the regulator is regulating. See item number 21 next to item 15, https://www.perfprotech.com/mercury...and-fuel-cooler/assembly/2691/80?umodel=20473

If fuel pressure is good, then do you think it is internal components of engine? I guess I was thinking engine was good because it runs decent with minimal load or most load in front of the boat and runs good when prop not engaged. Kinda starting to freak out now. Will be testing the pressure tomorrow.
Unfortunately, everything is suspected until proven otherwise with testing......With the mention of an overheat puts additional possibilities of having internal engine damage until proven not too. First start with outer accessories like fuel pressure, spark, timing, heat, air flow in, exhaust flow out, then head into the engine internals unless it's obvious you have an internal engine issue by noise, etc.. Sometimes internal engine damage is hard to locate sometime not...Just depends on the situation.

I certainly don't mean to freak you out, just want you to be aware of all possibilities in case you have to do more testing to find the issue... Lets hope for the best.:encouragement:
 

Therapydoc

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Checked fuel pressure at idle and 1500 rpm and it's right at 30. So that's good. Goin Wednesday to check under load. I flushed the cooling system again and didn't find any other impeller pieces.

Could the flame arrestor being dirty cause my symtpoms? It's pretty dirty. Is it okay to run the boat without the flame arrestor to determine if that could be the issue?

The thermostat seemed stuck. Was able to rotate it with pliers and get it loosened again. How do you remove one of those to replace it? Do you take pliers and squeeze the tabs and then rotate or what?
 

Therapydoc

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Took the boat out again today and it's running good now. I emptied the gas tank and cleaned the fuel pick up and it was dirty. Run clean fresh gas people
 

alldodge

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Glad to see your running and closing both similar threads
 
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