Change Carb to Fuel Injection

J

jamfred

New Member
Mar 10, 2009
92
Denver, Colorado
Boat Info
220 DA Sundancer
Engines
5.7L Mercruiser w/ Alpha I
Guys

I am looking into changing my 1990 DA220 from a carb to fuel injection. I have been looking into the Chevy TBI systems that I could pick up from any local salvage yard but I didnt know if this would possibly have a nagative impact instead of making my engine easier to start and so forth. Any ideas? It looks as though I can get into a used setup for under $250 for everything.
 
The injection maps are entirely different because of different performance curves. Auto systems rely on the O2 sensor, which isn't present on marine. The EFI has to be integrated with the ignition system and you can't do that at home without compromising ignition protection. If you are going to do this, you'll need a marine system.
 
If you're having a starting problem related to the carb, just get the carb rebuilt by a competent marine mechanic, or a newer generation carb. It will start much easier. Changing from this to a EFI system is a whole new game, not just a bolt-on.
 
I have the original quadrajet carb on right now and it starts ok but it seems that the fuel drains out of it after a sitting for a while. I know there are rumors of these carbs having issues with plugs cracking on them and causing the fuel to drain out plus you have to wait for the warm up period so you dont flood out the engine. Just trying to get away from this if possible but it looks to be more than I thought it would be.
 
I have seen on eBay and on Craigs List a couple of blown Mercruiser EFI motors that are being sold complete for under $1000. Includes computers, sensors, manifolds, EFI, etc. Easy swap when you have the whole package. A lot harder when you try to piece one together. A LOT harder.

Either pick up one of these, or get a whole new EFI crate motor.
 
One request. Find someone who has made this switch and is happy with the result before committing any money to the venture.

Those with experience will tell you the conversion will take more time and money than it is worth...at least if you want to end-up with a smooth and reliable engine.
 
gerryb said:
One request. Find someone who has made this switch and is happy with the result before committing any money to the venture.

Those with experience will tell you the conversion will take more time and money than it is worth...at least if you want to end-up with a smooth and reliable engine.
Click to expand...


Very true. Good advice! You may find a simple carb rebuild/swap to be the best alternative. Would definately be cheaper to.
 
Holley Projection has a system that is USCG approved that runs a throttle body on the speed density platform in open loop. This can be had for around $1000. Look up model 700-21 on Summitracing.com. Closed loop is better, but open loop should still provide acceptable performance.

This system is basically similar to a 350 GM TBI system.

http://www.summitracing.com/parts/HLY-700-21

Take this review I found with a grain of salt but:

"Take a pass on this system. The basic flaw of it's design is that it is trying to run the motor on a map based on only two sensors (Throttle Position and Coolant Temp) with an optional add-on O2 sensor. Not enough information for the system to run the motor well. Hard to achieve acceptable idle, which is pretty desirable when you are launching your boat off the trailer, and trying to get the boat back to the ramp.
Overall, the Holley 670cfm throttle body is good. It is in fact VERY good compared to the stock Rochester TBI 220 that it is based on. The adapter plates and brackets are good as well. The Projection 2D ECU is what makes this system run poorly.
To get a smooth idle, you need an Idle Air Control circuit being run from the controller, plus two additional sensors: an Intake Air Temp sensor and a Manifold Air Pressure sensor. The Holley Projection 2D ECU has no provisions for these, so if you try to use this system, you are fighting a loosing battle.
My Advice:
The simplest approach to making your marine engine fuel injected is to gather up all the parts your need from a factory fuel injected Mercruiser. Keep your eyes open for used Mercruiser EFI controllers and harnesses. Follow the Mercruiser manuals regarding the installation. (Mercruiser uses the Rochester TBI system, same as GM trucks but with a waterproof ECU) You will be in the water having fun with your boat faster than using the Holley Projection 2D system. But using all factory Mercruiser parts will be more expensive.
Home-Brew approach: Start with a Holley OEM Replacement TBI for 1980's GM 350 motors and any of the Holley adapter plates needed to mount the throttle body to your motor's intake manifold and connect up the throttle. If you have to buy a throttle body unit anyways, then Holley's is a very good TBI unit, and has the most airflow compared to Rochester 220 TBI units. I'm using this on a 305 Chevy/Mercruiser.
Keep your eyes out on eBay for any GM type 1227747 ECM (used on 1987 to 1991 C/K Pickups and Vans with Rochester TBI) and use a piece of tuning software (like TunerCat ) to modify a GM calibrator prom until you get acceptable performance...a stock truck calibrator prom for a manual transmission V8 will be a pretty close starting point for a Mercruiser 305 or 350. Get a spare too.. They are not water-proof and even if you mount it somewhere high on the transom, there's always the risk of it getting wet. Having a spare on the boat means not having to call SeaTow to bring you home!
This approach requires some study, but does work very well. There are on-line "how-to" articles written up by others who have adapted the GM TBI automotive system to a marine engine with better success than what Holley provides you it's kit.
My Disclaimer: I have no affiliation to any of the companies I've mentioned above. I just use their stuff for my own amusement, it is just a hobby to me. (i.e. I have nothing to sell, except perhaps a few left-over parts from my own experimentation ;-)"


Here is also a link where someone homebrewed a TBI system - http://home.hiwaay.net/~davida1/boat.htm

Doug
 
Last edited:
Without a dynometer and / or expert knowledge in the engineering of EFI, it's going to be damned hard to beat a carburetor without spending a lot of money, doing a lot of guessing, and perhaps breaking a few things. For example you can save a lot of gas money and have a nice smooth running engine by setting it up nice and lean of stoichiometric. But too lean and you'll also burn up the exhaust valves.

Full disclosure:
Yes this is something that I'd like to play with. But I'd need a pair of MEFI-4 ECUs, four wide-band O2 sensors and a bunch of pyrometers in the exhaust ports. Not worth the money for the learning experience.
 
Last edited:
The new Merc carb engines use electric fuel pumps.
Edelbrock makes a nice marine carb. Has metering rods that go through the jets for a more precise idle and low speed mixture
 
Here is a good option for you in your situation. I posted this on another thread.

Here are links to my reccomendations: http://www.summitracing.com/parts/EDL-2701/ for the applicable Edelbrock Intake
and
http://www.jegs.com/i/Holley/510/0-80559/10002/-1 for the Holley Marine 600 CFM Mechanical Secondary Carburetor.

Understand that with a mechanical secondary carb, you in effect have 2: 2bbl carbs with a progressive linkage. You don't wait for an air valve to open the secondary or rear barrels...you control when they open. You can feel them open...and when you have achieved your plane and or cruising speed, back off to the front two barrels for economy. If you need a bit of zip...throttle up a bit and you will feel the secondaries come in...you are in control.:thumbsup:

I used this same combo on a 260/Alpha in a 4400 Lb. Formular 242 SS with outstanding results.
 
sprink56 said:
Here is a good option for you in your situation. I posted this on another thread.

Here are links to my reccomendations: http://www.summitracing.com/parts/EDL-2701/ for the applicable Edelbrock Intake
and
http://www.jegs.com/i/Holley/510/0-80559/10002/-1 for the Holley Marine 600 CFM Mechanical Secondary Carburetor.

Understand that with a mechanical secondary carb, you in effect have 2: 2bbl carbs with a progressive linkage. You don't wait for an air valve to open the secondary or rear barrels...you control when they open. You can feel them open...and when you have achieved your plane and or cruising speed, back off to the front two barrels for economy. If you need a bit of zip...throttle up a bit and you will feel the secondaries come in...you are in control.:thumbsup:

I used this same combo on a 260/Alpha in a 4400 Lb. Formular 242 SS with outstanding results.
Click to expand...


I actually have that intake on my 49 chevy pickup with a BG Demon carb.

Thanks everyone for the replies. Looks like an electric fuel pump will assist as well as a new carb. Unfortunately I have had poor experiences in the past with holley carbs so I will be looking into a Edelbrock or Demon carb. I dont know if holley has fixed the problem of sticking floats but the ski centurion that I had was always having issues. We finally swapped the carb out and no issues after that.
 
jamfred said:
I actually have that intake on my 49 chevy pickup with a BG Demon carb.

Thanks everyone for the replies. Looks like an electric fuel pump will assist as well as a new carb. Unfortunately I have had poor experiences in the past with holley carbs so I will be looking into a Edelbrock or Demon carb. I dont know if holley has fixed the problem of sticking floats but the ski centurion that I had was always having issues. We finally swapped the carb out and no issues after that.
Click to expand...

I would venture to say that not all holley carbs are going to have that issue you experienced. Mine runs flawlessly and I know many others that have had great luck with holley carbs.

Demon carbs are based on the holley carb before they modify them.

Edelbrock makes a nice carb as well. I've run their 600 cfm on a vehicle application in the past. They are very sensitive to dirt in the fuel. If you're going to run them, make sure you have a good fuel filter setup. It may not hurt to double up on them as well. If the fuel contains sediment of any sort, the sediment will settle to the bottom of the 'fuel bowl' and lay there. As the sediment builds up, the jets begin to clog, and the engine will become very very hard to start. Once it does start, keeping it running will be the next challenge. The good thing about the Edelbrock carb is that the whole air horn assembly can be removed with about a dozen screws in literally 10 minutes. It's a very easy carb to work on.

With either carb you go with, I don't think adding in an electric fuel pump will help anything. All of these carbs will run on 6 psi fuel pressure which any mechanical pump can deliver.

Doug
 
You must log in or register to reply here.

Forum statistics

Threads
113,187
Messages
1,428,224
Members
61,099
Latest member
Lorenzo512
Back
Top