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Results 1 to 21 of 21
  1. #1
    Join Date
    Jan 2006
    Location
    Stratford, Connecticut,
    Posts
    61

    Default i Have a searay sedan bridge w

    i Have a searay sedan bridge with twin inboard mecruiser 255hp. i am repowing over the winter. i was considering the complete drop in bobtail engines with carbs. the mercury dealer was telling me if I bought the mpi instead I would see dramtic gph improvement over carbs. I would like to know if anyone has upgraded to mpi from carbs and seen these improvements.

  2. #2
    Join Date
    Aug 2006
    Location
    SW Ohio, USA
    Posts
    10,329

    Default "I haven't. But MPI is a

    "I haven't. But MPI is a great fuel economizer. The only downside is the cost to repair them vs. a carb. Turnkey (carbed) engines are reliable. If you are not concerned over fuel costs but are repairs then go carbed. MPI is very reliable but the cost of parts is off the wall while there is a savings in fuel costs, reliable quick starting and no fuel waste. Just like today's automobiles.

    If money is not an issue, go MPI and ask about a warranty package and weigh the costs."
    Fix minor things (replace wear items for preventative maintenance.) that cause major problems before they break.

  3. #3
    Join Date
    Jan 2006
    Location
    Stratford, Connecticut,
    Posts
    61

    Default "thanks guy, the warranty o

    "thanks guy,

    the warranty on the mpi is 3 years. how are the mpi? do they break alot or are they like my 1500 pickup 85,000 miles 10yerars old on nothing but regular maintainance and running great?"

  4. #4
    Join Date
    Aug 2006
    Location
    SW Ohio, USA
    Posts
    10,329

    Default I have no knowledge other than

    I have no knowledge other than a few posts on this site. They have been using MPI for years on Mercs. so I suspect they are as reliable as a car or truck as-long-as you follow the maintenance procedures and have a certified MPI technician available if a problem would arise. Ask for a 5 or 7 year MPI warranty if you agree to buy two engines--get it in writing from Merc.
    Fix minor things (replace wear items for preventative maintenance.) that cause major problems before they break.

  5. #5
    Join Date
    Aug 2006
    Location
    Calgary, Alberta, Canada
    Posts
    2,426

    Default "I swapped a carbed 4.3 out fo

    "I swapped a carbed 4.3 out for a 6.2 MPI this spring, and so far, so good.

    I like the simple starting with no dicking around with chokes, no smoking, missing etc during warmup. You just turn the key and she is running.

    The new ECM 555 seems to be improved over previous versions, and seems to be as reliable as those used in cars and trucks.

    Don't beleive the talk about wildly improved fuel economy. You will get some improvement, but it takes big tourque to push a boat through water, and that can only be made by burning a lot of gasoline. For normal cruising I think mine uses about the same as before with the 4.3, but when pulling skiers she sucks it up pretty good.

    Marine EFI's do not have feedback O2 sensors like in the auto world, so the mixture is not fine tuned for max economy. Marine EFI is closed loop, so it is an approximation of best air-fuel mixture, at best.

    Rod"

  6. #6
    Join Date
    Jan 2006
    Location
    Stratford, Connecticut,
    Posts
    61

    Default "thanks rod, thats pretty mu

    "thanks rod,
    thats pretty much what i thought also, the best part is the ease of starting."

  7. #7
    Join Date
    Apr 2006
    Location
    Rathmines, NSW, Australia
    Posts
    657

    Default "Hey Jeff Just thought the bo

    "Hey Jeff
    Just thought the boy from Oz would throw in his 10 cents worth here.
    As far as the fuel economy and performance of an injected engine as opposed to a carb engine, they are like chalk and cheese.
    The standard fuel injected engine will crap all over the standard carb engine, you will see far better fuel numbers, much easier starting and better all around performance out of your injected engine.
    BUT !!!! My only issue with fuel injected engines in a marine environment is that 0.2 of a volt drop accross a circute has the potential to give you some degree of a problem in a std computerised fuel injection system.
    What is the most comon cause of voltage drops in computer circutes, COROSION, what is abundant in a marine environment, the elements that cause corosion.
    Computer systems do not like salt or high levels of humidity.
    HOWEVER, if you pay particular attention to your wiring harness and connectors and use an apropriate corosion preventitive everywhere possible you will be just fine.
    The only other problem is the cost of componentry if say a computer or major sensor go's wrong but fortunatly that doesnt happen very often and besides its in a boat so you are used to throwing money at it.
    Yo HO Ho From downunder
    Peter C"

  8. #8
    Join Date
    Feb 2006
    Location
    Arlington, VA, USA
    Posts
    952

    Default My rule is NO BUTT CONNECTERS

    My rule is NO BUTT CONNECTERS - ever. Use GM Weatherpack connectors (with the proper tool) or solder and heat shrink connections.

  9. #9
    peter clarke's Avatar
    peter clarke Guest

    Default "Hi to all, I converted t

    "Hi to all,
    I converted two 7.4l engines from quadrajet carbs to MPI with edelbrock proflo MPI packages. I have yet to see better fuel consumption but probably will when I work out some kinks. I am already dropped 2gph per engine and I am set at 12.1:1 A/F. I plan to go up to 13:1 once I work out some fuel delivery issue and fuel temp. Can't beat the start up and cold idle and these engines have 1000 hrs on them. I think with the addition of a fuel cooler and air seperation tanks I can really dial these engines in. The beauty of the pro flo systems is you have total control over spark and fuel. These have O2 sensors but I use an digital A/F meter for tuning. But one better know what you are doing when your making adjustments.
    Peter"

  10. #10
    Join Date
    Apr 2006
    Location
    Rathmines, NSW, Australia
    Posts
    657

    Default "I am with you Mr Hays, I am s

    "I am with you Mr Hays, I am slowly replacing all my terminal joints with solderd joints, I then spray the join with silicon grease and then place heat shink over the join.

    Peter, with a bit of sorting out and a good fiddle you should be able to extract some good figures out of your engines eventually, BTW if you dont mind telling us what did it cost you to do the conversion.

    Cheers
    peter C"

  11. #11
    Join Date
    Aug 2006
    Location
    SW Ohio, USA
    Posts
    10,329

    Default I still use BUTT connectors bu

    I still use BUTT connectors but they have shrink tubing already on them. I do cut my wires and tin them w/solder before connecting them. I am not in a salt water environment so I will agree with you "old" I mean experienced boys for now.
    Fix minor things (replace wear items for preventative maintenance.) that cause major problems before they break.

  12. #12
    Join Date
    Feb 2006
    Location
    Arlington, VA, USA
    Posts
    952

    Default "Mr Clarke, Where do you mo

    "Mr Clarke,

    Where do you mount the O2 sensors for that Edelbrock MPI setup?"

  13. #13
    Join Date
    Dec 2007
    Location
    cuttingsville, Vermont, USA
    Posts
    10

    Default "Hi, This is Peter Clarke

    "Hi,
    This is Peter Clarke the guy with the converted 454's from carbs to MPI. To ansewer peter chamberlain's quetion, the edelbrock package I used cost me $2500 per engine. I did have some metal fab work that I did for throttle cables and coil mount. I think by the time I was finished I wouldn't be suprised if I had $3000 in each engine. To ansewer mistahays question is I mounted each O2 in the exhaust manifold thru the water jacket. How did I do that you ask, quite simple. I drilled a 2" hole thru the outer jacket, then welded a 2" pipe to the inner jacket inside the pipe and a second weld on the outside of the pipe to reseal the water jacket, then I welded a 1/2 block inside the pipe to have some meat to drill and tap for the O2. The only bummer about this step was that I was unable to keep the cast manifold from cracking on the inside so I ended up buying some GLM aluminum manifolds to finish this step. MY next step now that these are functional, actually I just finished a 1600 mile trip from VT to FL, is that I am getting some lean backfire from 3000 rpm and up and need to get rid of that. I know that my fuel settings are rich at 12:1 A/F so one of two things might be happening. First I might be getting air bubbles in the system either from the tank or from pump cavitation. So I plan to add a surge tank set up. I plan to do this by reinstalling my mechanical fuel pumps to feed the 1 gal tank. The HP pump will draw fuel from the surge tank, pump it thru the engine then back to the surge tank, then from there return to the main tank. If I configure the small tank properly any air bubbles in the fuel from the main tank will be separated out and rise to the top in the surge tank and be sent back to the main tank. Plus the HP pump won't have to lift fuel up the 24" suction tube in the main fuel tanks anymore. My second possible problem might be fuel temperture, engine room temps were averageing 115 to 123 degrees while underway so I might be getting some fuel boiling in the fuel rails. I also have been running these engines at 185 degrees to keep the ECM happy. It stayes in cold mode until 170 degrees. Anybody have a good source for fuel coolers. Also has anybody out there have any experience with surge tanks or built one.

    Peter Clarke"

  14. #14
    Join Date
    Nov 2005
    Location
    Newport Beach, CA,
    Posts
    189

    Default "Everyone talks about the fuel

    "Everyone talks about the fuel economy advantage that EFI/MPI engines offer, and rightfully so, they are more fuel efficent than carbed engines.

    What I don't see mentioned often, is the self diagnostic, self preservation, and data aquisition systems that EFI engines have that carbed engine do not. These are some very good features to have, and make the choice (in my opinion) a "no brainer".

    Dave"

  15. #15
    Join Date
    Feb 2006
    Location
    Arlington, VA, USA
    Posts
    952

    Default "interesting O2 mounting setup

    "interesting O2 mounting setup. I figured you would have trouble welding on cast manifolds - hense the cracking?

    "fuel settings are rich at 12:1"

    How does this work if you are using O2 sensors since their range is so narrow? Unless you're close to the stoich mixture, you're sensors will peg lean or rich. Hmmm

    Running at 3000 RPM under 75% load with a lean miss is a good way to fry an engine... as I'm sure you know.

    Definately agree with Dave N. Not sure i'm down with a $6k conversion, but if given the choice, i would always go EFI. The systems are just so logical once you understand how they work."

  16. #16
    Join Date
    Dec 2007
    Location
    cuttingsville, Vermont, USA
    Posts
    10

    Default "The O2 sensors that came with

    "The O2 sensors that came with the pro flo package are narrow band O2's. They don't tell you where you are in the A/F range, only if you are rich or lean. I couldn't add enough fuel to the mix to get them to show a rich indication at high rpm & heavy load. At one point I had the engines choking on there own fuel. When I put my digital A/F meter on which had a wide band O2 I was at 10:1. A friend of mine who builds high performance EFI engines told me that was typical of these Edelbrock packages to give a lean reading under heavy load. So I tune these with the digital meter. I basically will get to a certain RPM and hold it there and adjust fuel with the keypad in that RPM and manifold pressure range using the surround and conquer method. Once set I move up another 500 RPM and adjust again. They also give you three complete data sets you can save settings into so you can have say a really economical data set, a power data set, and something in between. But for the most part my load is aleways the same as is for most boats. I can run these in closed loop mode but I think I might end up too lean. Plus closed loop has parameters that need to be met in order to activate. 1800 to 3500 rpm and 4 or 5 inches of vacum. The 4-5 inches of vacum are the hard numbers to maintain. My boat is 34' and weighs 16000 lbs. On a smaller lighter boat I would bet you could get it to run in closed loop. As far as data aquisition goes I can record engine function with the digital A/F meter and review it on my laptop but I did not get the RPM recorder plug in when I bought the unit. There are lots of add ons if you want to spend the money to record all the data. I am not sure but I should be able to hook up a code reader to the ECM but I have not tried nor do I have a code reader."

  17. #17
    Join Date
    Aug 2006
    Location
    Calgary, Alberta, Canada
    Posts
    2,426

    Default "Does anyone know of software

    "Does anyone know of software available, or any other way to tweak the mapping for a Merc ECM 555 EFI?
    Rod"

  18. #18
    Join Date
    Feb 2006
    Location
    Arlington, VA, USA
    Posts
    952

    Default "Pete, Very interesting. I

    "Pete,

    Very interesting. I would find this more of an intelectual exercise and then simply have to beat it for competitive reasons.

    So from what it sounds like to me, you're well into rich at steady state cruise but your O2 sensors aren't indicating as such. You might not have your O2 sensors hot enough. You might try using heated sensors. Most cars these days use heated (three and 5 wire) sensors designed to get the system into close loop faster. Other than that, i can see no reason why you're getting lean signals at the O2 sensors.

    "wide range" oxygen sensors might tell you where you are for real but are about $5 hundy each last i saw.

    Your comment about vacuum reading paramiters is a good one. Most car EFI systems are designed to go open loop and full rich as you approach WOT. You may never get there.

    Sounds like you've got things on track with your method of adjustment. Other than fuel economy, i don't see any reason you need to be in closed loop mode. Its not like you need to pass emissions tests or have a catalytic converter that you risk frying by overfueling."

  19. #19
    Join Date
    Dec 2007
    Location
    cuttingsville, Vermont, USA
    Posts
    10

    Default "Mistahays, What do you t

    "Mistahays,
    What do you think about my air bubble in the fuel theory? I might be barking up the wrong tree.

    Peter"

  20. #20
    Join Date
    Feb 2006
    Location
    Arlington, VA, USA
    Posts
    952

    Default Not convinced. If you have nic

    Not convinced. If you have nice strong pressue and a regulated fuel return to the tank you shouldn't have an air or a heat problem.

  21. #21
    Join Date
    Dec 2007
    Location
    cuttingsville, Vermont, USA
    Posts
    10

    Default "I'm not totally covinced

    "I'm not totally covinced either but Mercruiser efi have a vapor removal system in their mid 90's big block efi setups. Plus they also have a two stage pump system which I don't have. Plus I don't think I have ever seen an EFI set up without a low pressure primer pump with the exception of mine. Thats why I think that I am getting some pump cavitaion. Usually they have some pressure feeding them on the suction side of the pump, I don't. When I had the pressure gauge on the fuel rail I always had steady pressure all the way up the RPM range. I would be curious as to what dave N thinks it could be. you there Dave?"

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