350 mag mpi RUNNING POORLY HELP

[Therapydoc]

Have a 2001 crownline lpx 225 with captains choice. The boat really bogs down and spits and sputters with any load. Boat runs fine without load. Tried with and without thru hull exhaust and makes no difference. I did lose the impeller first time out this year but it's been replaced and boat runs at right temp. I've back flushed all lines and they are clear. Boat did overheat and kill itself when I lost the impeller.

There's no take off at all. The exhaust pops and it sounds like the motor misses out. Could this be a distributor cap or spark plug issue? Or no since it runs fine without load.

Checked fuel pressure and I'm good at all ranges with and without load. Gas is all from this year and I have seafoam in it and octane booster.

Help before I decide to just sell it and get rid of the headaches.

 

[harleyman1975]

Before I finished your thread I was thinking cap rotor plugs and wires.

 

[jkust]

Has your boat been repowered with a more modern MPI engine or is it an EFI model? MPI for the 350 Mag came out for the 2002 model year and was EFI prior.

 

[wahlejim]

I would also do a quick compression test on the engine, it will tell you a lot about any internal damage that needs to be addressed. Check yur oil for any water intrusion as well.

 

[alldodge]

I see from your other thread that Fun Times was helping you but did not come back to answer you last questions about the flame arrestor, so you started another one for that.
http://forums.iboats.com/forum/engin...-low-end-power

If you don't get an answer just make another post like "bump" this will put your thread back on top and may catch others eyes

Since your fuel pressure is good, and other items have checked out, and since the motor has overheated, I to would suggest a compression test

 

[Therapydoc]

Has your boat been repowered with a more modern MPI engine or is it an EFI model? MPI for the 350 Mag came out for the 2002 model year and was EFI prior.

The top cover says mpi is why i said that. Serial number is omo74390 if that will tell you. Does anyone have the mercruiser part numbers for the cap and rotors and wires? I looked at the perfpro and their numbers don't pull up anything at my local auto parts store.

 

[Therapydoc]

I would also do a quick compression test on the engine, it will tell you a lot about any internal damage that needs to be addressed. Check yur oil for any water intrusion as well.

Oil has always looked good. Not milky or anything

 

[Therapydoc]

With the rotor and cap, an auto mechanic suggested maybe the problem due to the increased heat makes it worse which is similar to what I'm having.

As far as a compression test, can someone tell me how to go about doing that? I'm guessing you go into one of the spark plug holes with gauge but after that I have no knowledge or what to do. Can it be on muffs or need to be in the water ?

 

[Therapydoc]

Got the cap, plugs, rotor and wires changed out yesterday. Fired up and sounded good at idle. Revved up to about 2k rpm before engine was warned due to being on muffs and it has. Winding kinda noise at higher rpms. Not sure if the rotor isn't down all the way or if it's the impeller trying to keep up with little water supply (I don't remember it doing it before when on muffs though). Going to double check all wire placement again tonight. Anything else you guys would check ?

 

[harleyman1975]

There is another guy with an 5.7 mag that is experiencing a whinning sound as well. his is coming from one of the fuel pumps. (there is a high pressure and a low pressure pump (on some engines).

 

[alldodge]

As far as a compression test, can someone tell me how to go about doing that? I'm guessing you go into one of the spark plug holes with gauge but after that I have no knowledge or what to do. Can it be on muffs or need to be in the water ?

To do a compression test you will need a compression test gauge. Remove the connectors off the coil, this will keep the distributer from firing. Remove a spark plug and install the compression gauge. Crank the motor over a few times and check the reading on the gauge. Your reading should be around 150 psi and no cylinder should be less then 10% of any other cylinder.
https://www.amazon.com/dp/B000EVU89I...S5D5TFZMZ02H8Z

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?

Noticed from your last post on your other thread you made the above statement. The thermostat should not be turned if it has not been removed. Turning it inside the housing without removing the top will damage it. To remove the thermostat you remove the two bolts (item 7) and then the housing (item 1) to gain access to remove the thermostat.
http://www.mercruiserparts.com/bam/subassembly/31746/4848/140

Was this the part you are discussing?

 

[Therapydoc]

For the thermostat yes. Except mine is different. I have the two top bolts that hold the housing in place but there's no bolts that hold the actual thermostAt in place. There's just two tabs that stick out. Not sure if they get squeezed and then it pulls out or how it works

On compression test, I found another post that says you put a paper clip between a and b ports on diagnostic plug since its electronic. Do I need to do that as well?

 

[alldodge]

For the thermostat yes. Except mine is different. I have the two top bolts that hold the housing in place but there's no bolts that hold the actual thermostAt in place. There's just two tabs that stick out. Not sure if they get squeezed and then it pulls out or how it works

Going to need a pic on this one

On compression test, I found another post that says you put a paper clip between a and b ports on diagnostic plug since its electronic. Do I need to do that as well?

IMO no,
No need to put it in base timing mode. If there is no signal coming from the distributor (two connectors removed) the injectors don't fire nor does the coil.

Forgot, do put throttle in full WOT position. The WOT position allows for max air to be pulled in during test and also keeps injectors from firing

 

[Therapydoc]

May have found one issue last night. Was scavenging around under the engine to make sure I wasn't missing anything or seeing any tiny leaks or cracks. Never knew I could contort my body like that but that's another story for a different day.

Found a vacuum line that goes up to the throttle body and down to fuel regulator that was not connected. Maybe that was part of my issue? Not sure what that causes exactly bc my fuel pressure was always good but fingers crossed.

 

[alldodge]

With the vacuum line off, the regulator will cause the fuel pressure to increase 3 to 5 psi. The line will cause a vacuum leak but both of those IMO will not cause what your seeing, the vacuum line is to small and the pressure increase will help with increasing rpm

 

[Therapydoc]

Compression numbers are not good. On the port side I have 180 and 185 in front and rear but middle are both at 0. On the starboard side I have the same in front and rear and middle ones are 40 and 60.

Where do I go from here? Pull the motor? Geez I dread that

 

[alldodge]

Looks to me like the head gasket was blown. You might be able to get by with pulling the heads and replacing the gasket, won't know until the heads have been removed. The 180 number is high (could also just be the gauge), suggest turn the motor over without the spark plug to see if water comes out of it.

 

[WIMUSKY]

Sorry Therapydoc, your thread cannot be deleted per your request.........

Before I went any further I would use another tester and check compression again...........

 

[Therapydoc]

I got another gauge instead of the cheap one and the numbers are good 160-170 on all holes. Time for another test drive.

 

[Therapydoc]

Everything is looking good. I took it out again today and haven't had any problems.