Fuel inject a mercruiser 120?

[o'neal]

Is it possible to inject a mercruiser 120 with a throttle body setup? I would really like to get away from the carb,do a TB and pointless conversion in the dizzy.

 

[Bt Doctur]

Re: Fuel inject a mercruiser 120?

Kinda like reinventing the wheel.not worth it for the 4`s. Carbs work forever, 2 or 3 moving parts,all you need to do is KEEP IT CLEAN

 

[o'neal]

Re: Fuel inject a mercruiser 120?

True,BUT...I want quick starts,no hesitations,fuel to air maximized all the time as well as a ignition without points to wear out all the time and that dont throw timing out the window along with..besides the carb and points setup is all stone age technology and it is worth it to change over!

I'm thinking on using parts from a 2.8 chev?

 

[thumpar]

Re: Fuel inject a mercruiser 120?

If you want electronic ignition get a purtronix Ignitor II and Flamethower II. Skip trying to change the fuel side. My 120 had ZERO hesitation and used almost no fuel. I ran a 19 pitch prop at 4400+ RPM with no problem. Make sure what you have it properly maintained.

 

[hivoltg]

Re: Fuel inject a mercruiser 120?

The problem with tbi off an s10 or something will be the ecu with no O2 sensor. Hence reinventing the wheel.

 

[achris]

Re: Fuel inject a mercruiser 120?

... I'm thinking on using parts from a 2.8 chev?

The problem with tbi off an s10 or something will be the ecu with no O2 sensor. Hence reinventing the wheel.

I agree with you about the reasons for wanting to go electronic ignition and TBI... I tried to do it years back with my older 4.3LX... Ended up just buying a complete 4.3MPI. :facepalm:

As well as what hivoltg said, you must also consider the safety issues. Any TBI system from a car engine will not be marine certified, you'll run into insurance and liability issues.... Not to mention the risk of putting you, your boat and anyone on it into orbit... I think NASA has the monopoly on that at the moment....

As also already suggested, just convert the points to Ignitor II... Good system and you'll notice a difference just with that. I had an in-line 6 in the boat before the 4.3LX and I built my own CDI for it. Even though it still used the points (should have ditched them too) I noticed the difference. (BTW, when I say 'built my own'... I really do mean 'built my own'. Etched the circuit board and wound the transformer by hand!)....

Chris......

 

[o'neal]

Re: Fuel inject a mercruiser 120?

I just dont get the whole "I will blow up and catch on fire,not coast guard approved" regs.... I mean a carb still pump's fuel down the throat and its open to the atmosphere? You would think a TBI would be safer am I not right??

 

[Scott Danforth]

Re: Fuel inject a mercruiser 120?

No, you are not right. Marine carbs are fail safe in that they will not dump fuel anywhere but the throat of the carb.

Marine EFI is also intended to be fail safe. Automotive EFI is not. If your car leaks a little fuel, most people wouldnt notice until they smell it. If a boat leaks a little fuel.....BANG

Marine EFI also runs open loop all the time. Where automotive based runs closed loop when it comes up to temperature. Hence the reason your car has oxygen sensors. Not to mention you now have to deal with a return line to your tank, etc.

I agree with updating the ignition. However the fuel side is not worth it. A properly cleaned carb will start at the first click of the key. Simply give it a pump of the throttle to set the choke and give it a squirt of fuel, then turn the key.

 

[matt167]

Re: Fuel inject a mercruiser 120?

I'm not sure what is different with the marine TBI's vs the Auto TBI's. It may just be a marine certification with them. Carbs are definitely different, the vent is a J tube so it's vented into itself on a marine carb, and a marine carb has no vac ports. Among other things, gasoline vapors collect in the bilge so ignition protection is a good idea.. I have seen a bilge catch fire real quick due to a light hiccup while the spark arrestor was off for some tweaking, so YES it does matter..

On a side note, you could run a Megasquirt II ECU with a marine TBI and use no O2 sensors and only a MAP sensor and it would work, I just don't know how well you could tweak it.

 

[o'neal]

Re: Fuel inject a mercruiser 120?

Ok,I see.I will only change the ignition and just run with the carb.Thanks for the info guy's,fairly new to boats and I have a bad habit of modifying things to work better.....comes from my wheelin habit I'm thinking lol!

 

[christoner2002]

Re: Fuel inject a mercruiser 120?

The problem with tbi off an s10 or something will be the ecu with no O2 sensor. Hence reinventing the wheel.

On a older style fuel injection system, Like TBI, You can easily run the system without a 02 sensor. It has the computer running in open loop, rather then a slightly more efficient closed loop. My TPI system in my Camaro has run in open loop just fine since 2006. And I have noticed no fuel mileage/power differences with it.

I have thought about swapping to EFI on my boat also, but I think there is more to it then just swapping it over. A automotive system is mostly going to be running the vehicle at highway speeds, etc, with a overdrive transmission, keeping your rpm lower. Vehicles see high rpm's for mostly short bursts. Will the fuel mapping be correct for the higher rpm that our boats run at? Lots of unknowns that scare me enough, to not do it.

 

[o'neal]

Re: Fuel inject a mercruiser 120?

Varying speeds wont have an effect....What scares me the most is legality and what happens if checked.I know I can do the swap as a TBI swap is one of the easiest to make happen.

 

[Scott Danforth]

Re: Fuel inject a mercruiser 120?

If you have a fire, your insurance company wont cover you because its not CG approved.

If you really want TBI. bolt on a Holley Marine Pro-Jection system. They are cheep on ebay. then after you get frustrated with it and pull it back off in a year, you can resell it on ebay.

 

[matt167]

Re: Fuel inject a mercruiser 120?

You ~could~ use the regular Holley Projection ECU ( probably cheaper than Marine version ) with a marine TBI and have it USCG approved, but any self learning cannot be done without an O2 sensor.. It's simply not a good way to go.

 

[o'neal]

Re: Fuel inject a mercruiser 120?

Where can I get a good carb,either new or used for the 2.5 mercruiser then? Mine is unsafe-leaks fuel out the base(wet gaskets),continues to pour down the throat when shut down resulting in thin oil and a overfilled pan and runs way too rich and its not from the FP,bog's,wont get on plane....only thing it does well is idle. Been rebuilt twice and still has the same problem.

 

[thumpar]

Re: Fuel inject a mercruiser 120?

Has the float been replaced and adjusted correctly?

 

[o'neal]

Re: Fuel inject a mercruiser 120?

No and yes....Float looked good,no damage to them.not exactly sure where I set the floats and I cant find the paper with the info.

 

[thumpar]

Re: Fuel inject a mercruiser 120?

Does it have 1 or 2 mixture screws and what year it is? I would probably take it to a carb shop before trying to replace it.

 

[Scott Danforth]

Re: Fuel inject a mercruiser 120?

check to see if there is there fuel in the clear line running from the fuel pump to the carb? There should not. if so, the diaphragm of your fuel pump has a leak.

 

[Tail_Gunner]

Re: Fuel inject a mercruiser 120?

A little research is needed here I do not believe there is a USCG approved efi system if so plz post the reg's. As to adapting a auto efi system are you well versed in in efi...if so how do you plan to implement you OS sensor's. Post you ideal's it would be interesting and costly even if you can build your own tune,

By the way there will be little gain in performance or fuel economy but if you insist on going such a route Google dyno jet marine.