Electronic fuel injection conversion

islandsearay

islandsearay

Member
Apr 6, 2011
51
Puget Sound
Boat Info
1988 Searay 340 Sundancer, Twin 454.
Engines
340-Twin 454's Mercruisers V-drives.
I have a 1988 340 Sundancer with 7.4L engines mercruiser.
Thinking about the Sniper Quadra jet conversion from Holley.
It is a self tuning system.
I was wondering if anyone had done such a conversion and had any info on it.
My biggest concern from what I have read is the oxygen sensor location. ? Wet exhaust.?
Next is the need for a different intake manifold?

Next question is regarding distributor, does it need to be changed?

Have a great day!
 
What is wrong with your current carb system? It will be very expensive converting both engines to the system you are looking at. If properly set up your carb system is simple and reliable. The fuel injection will not gain you any meaningful amount of HP or fuel economy and introduce a more complex system that will be more troublesome over time. I suggest you keep what you have and get it running as it should.
 
islandsearay said:
Nothing wrong. Runs fine. Just a hotrodder at heart.
Click to expand...
Same here. My take is to keep the DFI conversions to the street and go boating. Being a hotrodder, you are a hands on guy, and simple systems are easily diagnosed and repaired in quick time.
 
Was looking around and found a link on it, so was looking at the Holley system and realized that the EFI would allow finer control of fuel system and upgrade would still look stock. The system appears to be simple to do. The only issue I see is having to drill a hole in tank to fit a return line. So now I am looking for a fuel sending and return line fitting that is similar to old fuel line pickup.
Currently reupholstering cushions and thinking about other items to replace/repair. she is an old boat but I want to update her and keep her in good condition.
 
Summit sells a 1 1/2" T with a NPT bung on it that you install on your fill line for just this purpose.
 
I have had her to thirty on water, loaded. GPS. I understand that SeaRay posted that this boat could do 42mph. Stock.
 
hottoddie said:
What is wrong with your current carb system? It will be very expensive converting both engines to the system you are looking at. If properly set up your carb system is simple and reliable. The fuel injection will not gain you any meaningful amount of HP or fuel economy and introduce a more complex system that will be more troublesome over time. I suggest you keep what you have and get it running as it should.
Click to expand...
I understand that. Just was curious if anyone had done it, before I splurge on something that will cause more issues.
Also would I need to change distributor to electronic ? I like my boat a lot. Have looked at other boats that are nice, but do not fit me. Mine fits like a glove. On a steep learning curve regarding boating. I find it exhilarating on water at speed.
My GF is a mechanic also, so we both enjoy the boat. She wants to stick with carbs. Under discussion.
 
No, 1.5" double barb fitting with a npt bung in the middle. You cut your rubber fill hose and put this in.
 
PMC said:
Same here. My take is to keep the DFI conversions to the street and go boating. Being a hotrodder, you are a hands on guy, and simple systems are easily diagnosed and repaired in quick time.
Click to expand...
I enjoy doing everything from wiring to fitting new components , repairs and so on.
 
scoflaw said:
No, 1.5" double barb fitting with a npt bung in the middle. You cut your rubber fill hose and put this in.
Click to expand...
Okay, does that close the loop on fuel system or do I still need to put fuel back into tank? It is the return line I am thinking about.
 
That's popular with the go fast crowd, you are going to need better heads and exhaust if you want to go faster.

Head over to OSO that's where the fast guys are
 
islandsearay said:
I understand that. Just was curious if anyone had done it, before I splurge on something that will cause more issues.
Also would I need to change distributor to electronic ? I like my boat a lot. Have looked at other boats that are nice, but do not fit me. Mine fits like a glove. On a steep learning curve regarding boating. I find it exhilarating on water at speed.
My GF is a mechanic also, so we both enjoy the boat. She wants to stick with carbs. Under discussion.
Click to expand...

Your distributors are already electronic, most like Thunderbolt IV. The spark is controlled electronically by the TB IV module. Decent system but the components are no longer available new. Some have changed over to HEI systems made by Delco, Mallory or DUI (Davis Unified Ignition). None will gain you any advantage over your TB IV system other than reliability and being able to get components when needed.

BTW no way a stock 340 Sundancer with V drives will do 42mph stock. maybe 42kph. I have 2 friends with 340ECs and each will do about 33mph. Even at those speeds the hull is very much chines walking and becoming more difficult to control. The 340 hull is not designed for that type of speed.
 
620-76300.jpg
cpperformance.com
 
I looked at the exact same conversion last year and the trick part is plumbing the return line. The guys at offshoreonly.com used one of three methods:

-Hole in tank (which I would never want to do)
-T fitting to fill hose (noted above)
-connect the line to the input spare port on the Water Separator

The O2 sensor is not a problem. It will raise the riser height about an inch on one side of the engine. Aluminum plates are available on Ebay and work great.

Where I ended up was going old school/new school. It is really difficult to fine tune carbs on a boat reading plugs. So, I installed two Air Fuel gauges with wideband O2 sensors on each engine. This gave me instant AF data on both engines which allowed me to change the jets to run close to 14.7 at idle and around 14 with the secondaries open.

I have been running 76s (primary) and 82s (secondary) for years. With the AF gauges in place.....I am running 74s and 76s respectively. The setup will probably pay for itself in the cost of gas.

If you think about it....that is what fuel injection is all about.....tuning the mixture to get as close and consistent to 14.7 that you can.

https://www.ebay.com/itm/AEM-X-Seri...:lEYAAOSwNPdbpyS3:sc:USPSPriority!22124!US!-1

https://www.ebay.com/itm/OXYGEN-SEN...451597?hash=item4b15de844d:g:NIkAAOSwWiBY-RWT

($178 gauge + $78 adapter) x 2
 
Does the manufacturer claim that system is approved for marine use. I'd be reluctant to consider it if it wasn't. Still seems like a cure for a disease that doesn't exist.
 
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