350 mpi swap from v6 carb

[jdubslopro]

Hey guys I have a Mariah shabah 202 that I rebuilt my carbed v6 (raw water cooled) in due to water ingestion/bad bearings. The motor got water in it again right after the rebuild so I bought a freshwater cooled horizon 350 mpi and just rebuilt it. Now I need a little help finishing up.
First, there is a water port on top of the intake manifold (not the one where the water manifold/thermostat housing goes) that my original motor didn't have. I'm running my original water pump (the guy that sold me the motor kept the freshwater closed cooling system for his boat).
It also has a fuel cooler that I need to plumb into the system somehow, but I don't know the proper way to make it work with my setup. I'm thinking of taking the hose to the exhaust manifold and running it to the fuel cooler and then back to the manifold, as the hoses appear to be the same size.
Also, there is a vacuum line from the fuel pressure regulator that I'm not really sure where it goes...there's no vac ports on the I/m.
Finally, read somewhere on this forum about the shift interrupt switch (this motor came from a bravo drive) that I would have to wire to the ecu (white wire) to prevent drive damage while shifting. If someone could point me to exactly which wire that would be very helpful. Also any insight or advice to the first couple things would be great.

 

[Bondo]

Re: 350 mpi swap from v6 carb

Hey guys I have a Mariah shabah 202 that I rebuilt my carbed v6 (raw water cooled) in due to water ingestion/bad bearings. The motor got water in it again right after the rebuild so I bought a freshwater cooled horizon 350 mpi and just rebuilt it. Now I need a little help finishing up.
First, there is a water port on top of the intake manifold (not the one where the water manifold/thermostat housing goes) that my original motor didn't have. I'm running my original water pump (the guy that sold me the motor kept the freshwater closed cooling system for his boat).
It also has a fuel cooler that I need to plumb into the system somehow, but I don't know the proper way to make it work with my setup. I'm thinking of taking the hose to the exhaust manifold and running it to the fuel cooler and then back to the manifold, as the hoses appear to be the same size.
Also, there is a vacuum line from the fuel pressure regulator that I'm not really sure where it goes...there's no vac ports on the I/m.
Finally, read somewhere on this forum about the shift interrupt switch (this motor came from a bravo drive) that I would have to wire to the ecu (white wire) to prevent drive damage while shifting. If someone could point me to exactly which wire that would be very helpful. Also any insight or advice to the first couple things would be great.

Ayuh,... Welcome Aboard,.... Got the serial numbers of the new motor,..??

The path yer takin', ain't gonna be easy, nor cheap,... I don't believe the 'puter can be grounded out like that,...

I believe ya need a Different 'puter...

The fuel cooler is plumbed as the 1st thing on the In-comin' water line...

Switchin' to raw water coolin' is gonna be a Major issue,... May not be able to pull it off,...
Due to the 'puter again...

 

[jdubslopro]

Re: 350 mpi swap from v6 carb

I'll have to check and see if the water intake line is the same id as the fuel cooler line. That'll make sense. I know the computer thing's been done to convert bravo to alpha, there's another member on this forum (Don, maybe?) that wrote in some other threads about it. Another way to do it would be simply to run a relay to interrupt power to the ignition coil, which I'm fully capable of doing, but I remember reading here somewhere about the "right way to do it" was to connect to a wire going to the "puter" as you call it.
Are you from nor'east as am I? (Western MA)
The serial tag reads M011557 meaning I believe it's 0M011557 as mercruiser leaves the first digit off the stamped tags. I've been using mercruiserparts.com for visual references.

 

[Bondo]

Re: 350 mpi swap from v6 carb

Are you from nor'east as am I? (Western MA)

Ayuh,.... Born, 'n raised in Downeast Maine,...

Now in exile here by the outlet of the Sweetwater Seas,...

 

[jdubslopro]

Re: 350 mpi swap from v6 carb

Ok I figured out where the vacuum port goes, and I mounted the fuel pump on top of the port side motor mount, looks exactly where it goes. The water line appears to be the right size to go inline with the raw water inlet. I'm thinking I can just remove the brass elbow on top of the intake manifold and substitute a plug, as water will enter through the top of the manifold from the water manifold. I've figured out all the wiring (I think) except for four wires. There is a black and a tan/white wire that both end in female bullet-style connectors, coming from the starboard side of the injector harness that carries the water temp plugs and manifold pressure sensor. There are also two wires (black and grey) that end in a two-terminal plug that extends from the port side injector harness, looks like it will reach to the power steering pump (which will be mounted at the top of the port side as it was on my v6) but I don't recall having a sensor on my PS pump.
My major issue lies within converting from a port-side mounted push-style throttle cable to a pull-style starboard-side mount throttle rotor. I rotated the throttle body 180 and it almost looked like it would work, except the bracket that the throttle cable attaches to wouldn't clear the mercathode, and it was facing the wrong direction. If I have to buy a different throttle body for this to work with my application, then so be it. Or will I have to swap out my hand throttle at the helm? Kind of at a loss with this one.
Finally, there is a threaded hole in the block, port side, to the top left corner of the freeze plug directly adjacent to the oil filter/oil pressure sensor (at around cylinder #7. Is there supposed to be a water plug in this hole? Or a sensor?

 

[jdubslopro]

Re: 350 mpi swap from v6 carb

Edit: found that second plug goes to the fuel pump.

 

[thumpar]

Re: 350 mpi swap from v6 carb

You are going to need a different drive or at least a different upper because of the ratio. I don't think you will be able to overcome the difference with a prop.

 

[jdubslopro]

Re: 350 mpi swap from v6 carb

I'll cross that bridge when I get there...but I'm hoping a 23p will do the trick. This motor is used with both alpha and bravo drives, albeit with a lower gear ratio, but I ran a 19p before. Well just have to see!

 

[QC]

Re: 350 mpi swap from v6 carb

Bondo has mentioned the 'puter . . . You need to know that the Closed cooling/Freshwater cooling system is setup with a higher temp thermostat, runs hotter because it can which is actually good. Bad for raw water cooled, AND the ECM ('puter) is now programmed to run with the hotter coolant temp. Do some searching and reading here, but this is a significant issue. The higher temp is bad for raw water cooled, and the ECM won't control the engine correctly if you run the lower temp thermo intended for the raw water setup.

Check for Alpha cooling system diagrams for the 300 MPI, that should answer the fuel cooler question. I can't get to my files now ('puter issues) but they are in the proper service manual.

 

[jdubslopro]

Re: 350 mpi swap from v6 carb

Drive lube level indicator...ok got all the wires figured out! Where is the warning buzzer normally located? I assume at the helm under the dash, but previous owners probably disabled it, there was a lot of hacked wiring when I bought it...

 

[Bondo]

Re: 350 mpi swap from v6 carb

I'm thinking I can just remove the brass elbow on top of the intake manifold and substitute a plug, as water will enter through the top of the manifold from the water manifold.

Ayuh,... The water flows Out of the intake manifold,....

You'll probably need a different T-stat housin', as yer's has No place for the in-comin' raw water...

The controller can be switched from pull to push...

'n yer Still not gonna be able to make the 'puter work anywhere near Right...

 

[jdubslopro]

Re: 350 mpi swap from v6 carb

If need be I can pick up a used freshwater cooling system...I thought it would be ok to run it as-is. I don't run in saltwater, would it be ok to just drop in a higher temp thermo? I believe the one in there is 170 from the original setup.

 

[jdubslopro]

Re: 350 mpi swap from v6 carb

Could you elaborate on changing the controller from push to pull? I looked into it a little last night, I found where a guy had put an LS1 in his boat and ran the throttle cable from the front of the block in order to control his throttle in the correct direction. I'm not opposed to this if I can find a way to make it work, but I'd like to do it the "right" way.

 

[Bondo]

Re: 350 mpi swap from v6 carb

Could you elaborate on changing the controller from push to pull? I looked into it a little last night, I found where a guy had put an LS1 in his boat and ran the throttle cable from the front of the block in order to control his throttle in the correct direction. I'm not opposed to this if I can find a way to make it work, but I'd like to do it the "right" way.

Ayuh,... Take the controller apart, 'n you'll see some holes to make it push, or pull the opposite way...

yer ignorin' the other REAL issues yer lookin' at....

 

[jdubslopro]

Re: 350 mpi swap from v6 carb

I'm going to give the guy that I bought the motor from a call and see if he's willing to part with the closed cooling system. I realize that a closed cooling system is able to withstand higher temperatures under pressure without boiling, so I'm going to do what I can to do this properly.

 

[jdubslopro]

Re: 350 mpi swap from v6 carb

I did some research, it appears the older carb models run a 143 degree tstat while mpi run 160. The newer ones all run 160 (including carb models). I'll double check to see what thermostat I actually have (thought it was 170 but I could've been mistaken). If I run into issues with it then I will convert to FWC. Thanks for the insight guys!

Edit: looked into it and the mercruiser oem part is a 160 tstat

 

[jdubslopro]

Re: 350 mpi swap from v6 carb

My only remaining issue now is the threaded hole next to the oil filter. If someone could help with that it'd be a great help. It's not the block drain as there is already a plug there. If its another drain hole ill pick up another plug and well...plug it up

 

[jdubslopro]

Re: 350 mpi swap from v6 carb

I was just re-reading all the responses, and I noticed you (bondo) mentioned "no raw water inlet". Since I'm using all my original external parts from the v6 including water pump and tstat housing there is the raw water inlet. Can't beat the deal I got on the new setup either...$400 and my v6. Plus rebuild kit ($550) and misc parts I'm only about $1200 into this project. Well, that and I spent $400 rebuilding the v6 in futility...

 

[QC]

Re: 350 mpi swap from v6 carb

Edit: looked into it and the mercruiser oem part is a 160 tstat

You need to check MPI plus Closed Cooling

 

[Howard Sterndrive]

Re: 350 mpi swap from v6 carb

there has to be an easy way to tell the ecu that the engine is hotter than it really is.
easier than going to closed cooling anyways.