Mercruiser 5.7L 350 EFI Alpha One Gen II Bogging Down

[jrivera]

Hello All......

Someone please give me some advice....

I have a 1999 Mercruiser 5.7L EFI Shortblock 350 and here is my problem....

The boat starts up right away with no problems and it idles great! From idle thru full throttle the engine is bogging down and will not go over 2k RPM's while its in the water..... The crazy thing is, while its out of the water with the water muffs hooked up, it revs up to 6k RPM's with no problem whatsoever..... I have replaced the fuel pump, fuel pressure regulator and fuel cooler and fuel filter. I have also replaced the spark plugs and coil. I also had the compression checked out and all cylinders are right around 160 which I was told was excellent..... The boat was sitting for 3 years when I purchased it..... I also replaced the Manifolds and Risers as well as the starter and alternator.... What could be the possibilities..... PLEASE HELP!!! THANK YOU!!!!

 

[njmedic3306]

Re: Mercruiser 5.7L 350 EFI Alpha One Gen II Bogging Down

I am not an expert but here is my initial response.

1. I have seen motor problems act up only when the motor is under a load. Everything from cracked blocks to carb problems.

2. As far as your problem I would focus on the carburetor. It sounds like maybe a float is sticking or a needle valve is gummed up. ESPECIALLY if the boat was last run 3 years ago and it still has the same gas (without stabilizer). My buddy works on marine motors and says Ethanol is horrible to carburetor.

Maybe other can chime in.

 

[NHGuy]

Re: Mercruiser 5.7L 350 EFI Alpha One Gen II Bogging Down

EFI engines are managed by an electronic control module. You may want to have the ECM scanned, there could be a stored code to lead you to the solution. Possible crank sensor problem, but don't go out and buy parts without a diagnosis. That's just guessing.
How is your battery state of charge?
The last post didn't see your "EFI" system, there is no carburetor to check. But he does have a point about fuel age and condition. It must be fresh and clean, as must the filters.

 

[jrivera]

Re: Mercruiser 5.7L 350 EFI Alpha One Gen II Bogging Down

Ok, so today I opened up the Fuel Injection Throttle body thinking it could be the fuel injectors and noticed a bunch of rust and cracked o-rings so I replaced both injectors and all gaskets and o-rings, pretty much rebuilt the entire throttle body and brought it into the water, had the same problem!!


You mentioned maybe cracked heads..... I noticed today while the boat was out of the water, hooked up to water muffs, when I gave it gas, brown water was blowing out from the exhaust instead of clear water, I also noticed that brown liquid about twice while riding in the water..... Do cracked heads cause that to happen?

I was also thinking maybe the TPS was bad..... could a bad TPS cause loss of power while on the water but none while off the water??

 

[jrivera]

Re: Mercruiser 5.7L 350 EFI Alpha One Gen II Bogging Down

EFI engines are managed by an electronic control module. You may want to have the ECM scanned, there could be a stored code to lead you to the solution. Possible crank sensor problem, but don't go out and buy parts without a diagnosis. That's just guessing.
How is your battery state of charge?
The last post didn't see your "EFI" system, there is no carburetor to check. But he does have a point about fuel age and condition. It must be fresh and clean, as must the filters.

Ok, I have probably cycled about 50 gallons thru the engine already and there was only a little bit of fuel in the tank, when I bought it. Some of it looked a little gel like so I put in a can of seafoam. I put a second fuel filter before the main fuel filter to see if any of that gunk was going through the lines and it was not.

I think its going to be either the crank sensor, cracked block or TPS sensor. By the time Im done fixing this engine, it will pretty much be rebuilt!!!

I will also get the ECM scanned, great suggestion!!

 

[jrivera]

Re: Mercruiser 5.7L 350 EFI Alpha One Gen II Bogging Down

***Bad News Update***

I installed the new TPS sensor today and when I went to crank her up, she would not crank..... I pulled out a spark plug, and low and behold, there was water in the cylinder...... As I removed each and every spark plug, there was water in each cylinder!!!!! That must have been that brown liquid coming out of the exhaust yesterday!!! This whole time, that must have been what it was, maybe started off w/ a small fracture and finally gave up yesterday.....

Could that be a bad head, block or head gasket?

I am taking out the head today to bring it to a machine shop to have it tested. If the head is good, than im thinking its going to be the block and not the head!

If the heads were bad this whole time, why did I get a good compression reading through all of the cylinders??? Im confused.....

Any suggestions???

 

[6meter]

Re: Mercruiser 5.7L 350 EFI Alpha One Gen II Bogging Down

Do a leak down test before you tear it apart.

 

[jrivera]

Re: Mercruiser 5.7L 350 EFI Alpha One Gen II Bogging Down

How do I do a leak down test when theres water already in the cylinders?
I guess what Im trying to figure out is, what will a leak down test tell me, if theres water already in the cylinders?

Thanks again!

 

[zbnutcase]

Re: Mercruiser 5.7L 350 EFI Alpha One Gen II Bogging Down

My suggestion? Take it to a MARINE service professional!

 

[jrivera]

Re: Mercruiser 5.7L 350 EFI Alpha One Gen II Bogging Down

I dont want to pay those outrageous charges from a Marine shop.
Its a regular car engine except for some minor differences. I will just take my chances with advice from this forum and my awesome mechanic. I will still come out better in the long run bc I will know exactly what is being done and I wont be ripped off by crooked marine shops! We have pretty much trouble-shooted every possible option and tried every alternative and have came to the conclusion that its the heads or the block. I have a set of heads and blocks sitting at my mechanic's place in case that is what it is!
It really cant be anything else bc we have changed everything on that engine, except for the head and block!!!