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5.7L Mercruiser EFI Conversion


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I just purchased a 1990 Malibu Euro f3 with the 5.7L Mercruiser engine and want to convert it from cabureted to EFI.  Are there any suggestions on what kit is best to install?

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22 minutes ago, 23LSVOwner said:

Personally, if I was going to go with an aftermarket kit I would use this one:

 

https://amzn.to/356jJHf

 

It is self tuning which will save you a ton of aggravation.

Do you have personal experience with that set up?  It looks like a good kit.

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11 hours ago, solorex said:

I am sure the kit is good.  But why do you want to covert?  Carb is so simple and reliable.  

 

9 hours ago, SkiPablo said:

there is no real advantage to doing this - are you having acceleration issues or starting issues ?

My carb is tuned well, but that initial start is still finicky.  An operator needs to know the difference of "not enough gas" versus "she's getting flooded".  My wife, daughter, and oldest son do not know the difference.  My middle son is different, and knows it all like me.  After it's warm and that initial start is there, no problem.

Also, if you are changing elevations, that can be an issue too.

So I can see the benefit.  Heck I just put a rebuilt carb on last summer but this still has my interest.

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@coobrad @23LSVOwner @Michigan boarder - Looking at the kit it appears to me the calibration (learning) process uses an O2 sensor, fine for automotive but most O2 sensors are not water compatible coupled with most ski boat exhaust manifolds mix the water at the elbow so you need to find an appropriate spot for dry exhaust sampling.  Also, that requirement will drive your price up significantly to find suitable manifolds or modify existing ones for that system.  

@coobrad - You are probably ahead in either a good carb rebuild or like what @Michigan boarder did in purchasing a carb from a reputable vendor.  The Weber carb is very tunable and works really well, as he also noted cold starts are a bit finicky and it may take a bit to learn the proper choke settings.

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On 11/7/2020 at 9:58 AM, Woodski said:

@coobrad @23LSVOwner @Michigan boarder - Looking at the kit it appears to me the calibration (learning) process uses an O2 sensor, fine for automotive but most O2 sensors are not water compatible coupled with most ski boat exhaust manifolds mix the water at the elbow so you need to find an appropriate spot for dry exhaust sampling.  Also, that requirement will drive your price up significantly to find suitable manifolds or modify existing ones for that system.  

@coobrad - You are probably ahead in either a good carb rebuild or like what @Michigan boarder did in purchasing a carb from a reputable vendor.  The Weber carb is very tunable and works really well, as he also noted cold starts are a bit finicky and it may take a bit to learn the proper choke settings.

 

Pretty sure the O2 sensors on boats are not in the water flow. Otherwise they would die all of the time.

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48 minutes ago, 23LSVOwner said:

 

Pretty sure the O2 sensors on boats are not in the water flow. Otherwise they would die all of the time.

That was exactly @Woodski's point.   If you are going to run closed loop you need O2 sensors, and they need to be dry.  Adding O2 sensors would pretty much require a new set of manifolds since the ones on that motor can't easily be fitted with sensors.  New manifolds would boost the cost of a kit to several thousand more, and for what?

My vote is to keep the carb and put in a manual choke cable.  Anybody can learn to recognize the sound (and smell) of lean vs rich, and we're only talking about a few minutes of rough running anyway.  Better yet, put a spring on the cable so you have to hold it out if you want choke.

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These might help. 

I'd check but that mercury riser spacer may be fit into your exhaust. If not you may be able to get one made for yours. 

https://www.hardin-marine.com/p-104396-o2-spacer-stock-mercury-riser.aspx

https://www.hardin-marine.com/c-391-o2-sensors.aspx

https://www.holley.com/products/marine_and_powersports/marine/

 

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22 minutes ago, cowwboy said:

These might help. 

I'd check but that mercury riser spacer may be fit into your exhaust. If not you may be able to get one made for yours. 

https://www.hardin-marine.com/p-104396-o2-spacer-stock-mercury-riser.aspx

https://www.hardin-marine.com/c-391-o2-sensors.aspx

https://www.holley.com/products/marine_and_powersports/marine/

 

Those spacers would work as long as the hood will close over them.  You could always use a trim ring under the hood to lift it if you need to.

By the way, I disagree about the reasoning they use for cats on the spacer page.  Water vapor is not what kills O2 sensors, it is nitrogen compounds (the nitrogen comes in the intake air) that mix with the water vapor in the heat (and later in the upper atmosphere) to create nitric acid (cause of the dreaded "acid rain" of the 1980's).  The cats convert the NO and NO2 into water and N2, which is a stable molecule and won't damage the sensors.  Water and N2 are both found in great quantities in the atmosphere, thus solving the acid rain problem.

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