Conversion from Carb to EFI

[RayTCraft]

Hi Everyone

Brand new to the forum (looks great). I am doing a rebuilt of my 1990 4.3L MerCruiser and was pondering a conversion from 2BBL carburator to EFI. Has anyone done one or know of someone who has I am aware that many parts used on marine application powerplants use special marine parts. I have aquired a complete 4.3L Vortec out of a 1993 Jimmy (for the block, mine is cracked) and my plan would be to combine the two for the conversion. Any advice/information would be appreciated

 

[boaterG]

Re: Conversion from Carb to EFI

you should be fine using the block , however you need to find someone who has a fuel injected 4.3 to see where the O2 sensor is mounted to convert to fuel injection you will also need the computer . If you could find a salvage boat to get all the parts from it would be great .

 

[Ole Sarge]

Re: Conversion from Carb to EFI

I have never done this conversion to a boat, but I did it successfully to my 71 Scout 345. You would need the ECM from the doner, full wiring harness, and all the sensors. I also am not sure where the O2 sensor would go. I believe you would need a closed loop system (unlike your donor system) which would have no O2 sensor. I'm sure there is lots of info on the web, one place that really helped me figure out my setup was www.binderplanet.com, look under fuel injection on the main page. Good luck, I hope you get it to work.

 

[flargin]

Re: Conversion from Carb to EFI

I have a marine commander, a Holly marine EFI Conversion kit, but I don't know if they have a unit for the 4.3. It helps with my altitude changing problems (I run from 3000' to 9000')

I don't know if I would invest the money (I bought it this way)

If you go with a homebuilt there are concerns about making sure it is marine ready... can't help you there.

 

[Radeonx]

Re: Conversion from Carb to EFI

pull a 4.3 and all the parts out of a jimmy / blazer / bravada out of a salvage yard. would be your cheapest bet. as for the O2s, im sure you could have bungs fitted on the exhaust for them.

 

[mylesm260]

Re: Conversion from Carb to EFI

a 1996 or newer 4.3 vortec will net you about 30-40 more HP (vortec heads)

I myself used the automotive EFI, intake manifold, wiring harness, ecu and everything.

I just had to modify the wiring harness a little bit and run a couple relays. I used a relay in series with the + feed to the coil pack for my shift interupt.

Boat went from 45 MPH to ~60 MPH (19P prop to 23P prop) after the upgrade

That was also going from a 2bbl non vortec odd fire 4.3 to an EFI'ed vortec even fired 4.3


Hope this helps.

 

[mylesm260]

Re: Conversion from Carb to EFI

EFI works by sensing engine load, and delivering the correct amount of fuel.

There are two ways to detect engine load.

#1. Manifold Absolute Pressure. As you open the throttle, the vacuum in the manifolds decrease, a map sensor reports this to the ECU, and along with other inputs (TPS, CTS, ATS, etc) it gives the correct amount of fuel.

#2. Mass Air Flow. A sensor measures the amount of air going into the engine. The sensor reports this information to the ECU, and the ECU calculates how much fuel to give.


When tuned properly, both systems work fairly good. But here is the major major difference.


MAF based systems can adapt to changes, and MAP based systems cannot.
Furthermore, MAP based systems rely heavily on o2 sensor inputs. MAF based systems only use the o2 sensor inputs for "fine tuning"

O2 sensors are only good for 60,000 miles, 85% of the cars on the road older than say 1999 are running with dead o2 sensors. In the end it ends up hurting mileage by 5% and emission.


So long story short, running an MAF based efi system without the o2 sensor is perfectly okay, you will just loose a tiny bit of fuel efficiency and you're emissions will be off.




Because my engine is now in a boat, my VE table (volumetric efficiency) has changed. Marine exhaust flows much better than truck exhaust (15' of pipe with 2 mufflers, 2 catalytic converters vs 4 ' of pipe down the leg) Because I'm using an MAF based system, my EFI is automatically adjusting for this (it's actually measuring the increased air into the engine)

IF I took a MAP based system and put it in a boat, I would be running lean, because even though my manifold pressure would be the same, my engine would be flowing better. More air + same fuel = running lean.


So long story short, you don't need O2 sensors. Trucks run fine without them, and therefore a boat with the same EFI system runs fine without it. If I connect my OBD2 code reader to my wiring harness, I actually get 8 error codes. 4 saying that my 4 o2 sensors arn't giving any outputs, and 4 saying that the 4 heaters in my o2 sensors are "open". Engine/boat still runs great.

 

[180shabah]

Re: Conversion from Carb to EFI

Couple quick thoughts here - that 93 4.3 may say vortec on the valve covers, but it does not have the real vortec heads, it has the TBI heads which are probably the worst heads to ever come from GM for making any power. Couple that with the intake manifold for the TBI from the truck and your net power gain will probably be a LOSS. I would use the block from the truck, but reuse your existing heads(if they are still good), intake and carb. This will give you the same power/performance that you have now and cost the least. Upgrade options are all over the place - 4bbl, vortec heads, aftermarket intake manifold, or any combination of the above for varying levels of power and expense.

FWIW - Dennis Moore sells "risers" that allow O2 sensors to be installed prior to the elbow.

 

[mylesm260]

Re: Conversion from Carb to EFI

"limp mode" doesn't really exist in 95% of automotive EFI. (the one vehicle I can think of off the top of my head that truely has a limp mode is the 32 valve Cadillac northstar)

Like I said, o2 sensors fail ALL the time, they're only good for about 60,000 miles in a car/truck. IF that was the case, half the cars on the road would be in "limp mode"

It's referred to as "open loop mode" meaning there is no feedback to the ECU from the exhaust.

on 1996 and newer vehicles, when the o2 sensors fail, it's supposed to set off the check engine light, although that's not always the case.

 

[mylesm260]

Re: Conversion from Carb to EFI

Couple quick thoughts here - that 93 4.3 may say vortec on the valve covers, but it does not have the real vortec heads, it has the TBI heads which are probably the worst heads to ever come from GM for making any power. Couple that with the intake manifold for the TBI from the truck and your net power gain will probably be a LOSS. I would use the block from the truck, but reuse your existing heads(if they are still good), intake and carb.

agreed, 1996 and newer is defiantly more desirable as it is truly vortec.

One thing to keep in mind, mixing and matching piston/head combinations from different generations can lead to different compression ratios (or possible even interference) . Make sure you research the head CC and the dish of the pistons (as well as the deck height) before you mix different heads with pistons.

I also believe the vortec heads have matched pistons, meaning that you need both to get the benefits of "vortec" HE would be MUCH better off starting off with a 4x4 or AWD 4.3 vortec from a 1996 or newer. Then he can leave the long block 100% in tact. The cam, the pistons, the heads would already be good to go.

 

[ryendube]

Re: Conversion from Carb to EFI

agreed, 1996 and newer is defiantly more desirable as it is truly vortec.

One thing to keep in mind, mixing and matching piston/head combinations from different generations can lead to different compression ratios (or possible even interference) . Make sure you research the head CC and the dish of the pistons (as well as the deck height) before you mix different heads with pistons.

I also believe the vortec heads have matched pistons, meaning that you need both to get the benefits of "vortec" HE would be MUCH better off starting off with a 4x4 or AWD 4.3 vortec from a 1996 or newer. Then he can leave the long block 100% in tact. The cam, the pistons, the heads would already be good to go.

Vortec benifits are this, foremost is the new designed heads. They will be a centerbolt valvle cover and the intake bolts will straight not angled like older style intake head match up. The heads get there increased power by a newer design combustion chamber called fast burn or something i ferget and am to lazy to look up.The new combustion chamber is smaller I know for the 5.7 mine is aprox 62cc, also the spark plug is more centraly located. All these improvements make them the best stock head you can ever get from a GM motor. no "double hump" or whatever antique head will give you these benifits. if you wanna get crazy I got mine machined and the 5.7 heads are flowing 290cfm @550 lift. its nuts. K secound benefit of the vortec engines is they are roller motors meaning roller lifters are used, cam is a roller cam. this also means you have to use a roller cam if your replacing with a marine cam.


As far as sensors go, O2 sensors are important as is a speed sensor on these motors if you want true performance and not a inefficient gas guzzler. 4 o2 sensors are used on V8 and I believe 3 on V6 they are 4 wire o2 sensors meaning they are HEATED. They are not the older TBI setups with one sensor etc. ( I have built 2 S10 trucks with a 98 and a 99 5.7l vortec, all from scratch went through every wire in the harness every setting had the GM master manuals reprogrammed computer etc etc etc it was my dream nobby in my 20s)

If you have the older (93 you said) its pretty much junk well not junk just not a desirable setup. TBI is just an electronic carburator definetly alot easier to setup and modify.

If i were to do the vortec setup I would either A get true vortec motor and buy a carburetor intake and make it carburated. B make it TBI or
C if was serious about going nuts then I would look into reprograming the computer or using a "trick" box on the harness. Those holley boxes or Holix (i think thats them) are expensive and are only feasable for hot rod or boat indstalls. your better of buying the intake and carbing it.

 

[ryendube]

Re: Conversion from Carb to EFI

as far as piston matching stock motors are going to have either dish or flat top pistons with reliefs. worse cause would be lowering the compression. valve to piston clearance should not be a problem.

Another note the one down fall to the Vortec is their cam profile and the lifter springs. They perform poorly at high rpm (they are truck motors) and if you wish to up the cam profile you will need to get new valve springs installed in head.

 

[mylesm260]

Re: Conversion from Carb to EFI

As far as sensors go, O2 sensors are important as is a speed sensor on these motors if you want true performance and not a inefficient gas guzzler. 4 o2 sensors are used on V8 and I believe 3 on V6 they are 4 wire o2 sensors meaning they are HEATED. They are not the older TBI setups with one sensor etc. ( I have built 2 S10 trucks with a 98 and a 99 5.7l vortec, all from scratch went through every wire in the harness every setting had the GM master manuals reprogrammed computer etc etc etc it was my dream nobby in my 20s)

I'm telling you the o2 sensor makes very little difference. I've actually built 3 EFI systems from scratch (megasquirt) and tuned them from scratch, with wide-band o2 sensors. Once the system is set up, the o2 lamba is only + or - 5% AFR.

99% of carbs out there are Way further than +/- 5% off stoik.

And the v8's and v6's have the same # of 02 sensors. 1 at each manifold, one before the cat and one after the cat (To verify the cat is working) OBD-2 complience.

If o2 sensors were important on EFI systems, then why have boats had EFI for over 10 years without them? The ONLY reason they added o2 sensors now is because they're required by law for 2010 emissions laws.


IF you take 99% of automotive systems out there, and disconnect the o2 sensor:

1. You're engine will run the exact same (performace wise)
2. You're milage will decrease by 1-10% (usually around 5%)
3. You're emission will increase significantly.
4. You're check engine light will come on
5. You will fail air-care (or state emissions testing if applicable)

For those of you who do live in areas that test car's exhaust, have you not ever had this happen to you?

1. you take you're car/truck to be tested
2. you fail, even though to you're knowledge your car runs perfectly
3. You take you're car/truck to you're mechanic and they tell you you need to replace you're o2 sensor(s) to pass (meaning that you're sensor was dead and not doing anything)

Where I live (vancouver BC canada) we have air-care, it is extremely common for vehicles to fail because of a bad o2 sensor and not know it.

 

[mylesm260]

Re: Conversion from Carb to EFI

Another note the one down fall to the Vortec is their cam profile and the lifter springs. They perform poorly at high rpm (they are truck motors) and if you wish to up the cam profile you will need to get new valve springs installed in head.

Boats have three major issues that makes this a non issue.

#1. They need a lot of bottom end torque to get up on plane

#2. They require cam profiles with very little to no overlap, or they will ingest water at low RPMS.

#3. High RPMS (5000+) quickly wear engine and drive components.


Because of these 3 factors, the desirable RPM for peak HP is 4400-4800.

The truck vortec 4.3's get peak HP @ 4400, pretty much exactly what you want anyway. While there is SOME wiggle room for hotter cams, there isn't very much.

 

[ryendube]

Re: Conversion from Carb to EFI

If o2 sensors were important on EFI systems, then why have boats had EFI for over 10 years without them? The ONLY reason they added o2 sensors now is because they're required by law for 2010 emississipons.

boats do not use the same ecu that trucks

also you are correct that O2 sensors will not make a huge difference I was stating that with that era of motor they make MORE of a difference. V8s use 4 V6s use 3 due to the fact V8 has dual exhaust dual cats where a v6 uses a y pipe prior to the cat.

The speed sensor is also used for fuel enrichment in congection with the O2 sensors. I built my first v8 conversion while I was in school and had access to the actual GM manuals (4 like 1000pg books just on that particular motor)on those motors and there is alot more going on between the sensors than most take for granted.


I agree with what you said about the cam profile and torque range I was merly pointing out that if a cam swap was being considered this is soemthing that has to be considered. I always thought boats liked a more steady torque curve.

regardless performance wise and to simplify i would just carb it. for the person who started this is not very knowledgable on these motors or conversions. Carbing it will give you great performance and greatly simplify the install.

 

[ryendube]

Re: Conversion from Carb to EFI

IF you take 99% of automotive systems out there, and disconnect the o2 sensor:

1. You're engine will run the exact same (performace wise)
2. You're milage will decrease by 1-10% (usually around 5%)
3. You're emission will increase significantly.
4. You're check engine light will come on
5. You will fail air-care (or state emissions testing if applicable)

these statments are not possible. you cant have both. the main pollutants is no2 which is effected greatly by timeing of the motor, and hydro carbons which is unburnt fuel again timeing and fuel delivery effect these . They react on a logorithmic curve opposite to each other ie you can hook up your car/truck to a emmision sniffer run in test mode and play with settings and watch the realation to each other. This is because how the STOCK computer is programmed. YES you can run an efi without O2 sensors but modifications must be made for it to run well. You state you built 3, did you leave stock computer in the setups? As well you cant adjust the timing on a vortec to compensate. (how many times I asked what the hell are you trying to do when I watched old timer spinning the cap on a vortec motor)


to wrap up I am saying a true vartec is an awesome motor however you need to modify, a stock TRUCK ecm will not perform well. to waste over 1000$ on a new ecm is a waste unless you are dead set on EFI. for a few hundred you can get a carb and an intake. performance will be roughly the same.

 

[mylesm260]

Re: Conversion from Carb to EFI

these statments are not possible. you cant have both. the main pollutants is no2 which is effected greatly by timeing of the motor, and hydro carbons which is unburnt fuel again timeing and fuel delivery effect these .

You are forgetting to factor in the catalytic converter. The o2 sensor optimizes the emissions to a range that is acceptable to the catalytic converter. If you remove the o2 sensor, and your emission from the engine to the cat increase by 25-50% than the emissions from the actual tail pipe go up by as much as like 1000%

I have the air-care papers to prove this. I failed by a massive margin, changed my o2 sensor and passed with flying colors.


Think about it this way. O2 sensors data generally shapes fuel mixtures + or - 5%

IF you had a carbed car or boat, and you adjusted you're jets for 5% more or 5% less fuel, would you notice any difference driving it?

This is because how the STOCK computer is programmed. YES you can run an efi without O2 sensors but modifications must be made for it to run well. You state you built 3, did you leave stock computer in the setups? As well you cant adjust the timing on a vortec to compensate. (how many times I asked what the hell are you trying to do when I watched old timer spinning the cap on a vortec motor)

People need to learn some things about how EFI works to understand how programming works.

EFI handles Fuel and Spark.

Fuel wise, it wants the proper Air/Fuel ratio for optimal power, emissions and fuel economy (all 3 factors have pretty much the same desired air/fuel ratio of 14.7)

Spark wise, it wants as much ignition advance as possible without detonation. Modern systems incorporate knock sensors so the ignition is advanced to the point that the engine is on the verge of knocking.

Weather you're in a boat, or a plane, or a car, these factors are always the same.


A speed density system will have the exact same tuning in a boat as in a truck, given the same internals, injector sizes and cam.

The boat *MAY* run a little bit leaner, to make more power, at the expense of emissions, but that's unlikely.

The only real difference is the o2 sensors for closed loop mode.

Closed loop mode is necessary for catalytic converters to work, this is the primary reason cars have o2 sensors.

In 2010 all boats have new emissions standards, it's no surprise they've added both catalytic converters and o2 sensors.

And if anybody compared a 2009 vs a 2010 boat motor they will most likely notice:

1. A higher cost
2. The same power output
3. Slightly better fuel economy
4. emissions that are 1/20th or less

 

[ryendube]

Re: Conversion from Carb to EFI

``EFI handles Fuel and Spark.``
umm what else is there to control in a motor? oh **** thats right it also controls combustion chamber volume in effect increasing compression.... by way of the EGR valve..........

thanks but I understand fully how a efi system works, you are generalizing and simplyfying them.

Anyways Thread starter if you are interested I have the pinouts and description pages for every circuit on that motor, Ive traced every wire in the vortec setup already and can tell which to omit and which are required. Most likely you will be buying a wrecker setup which ,will from a truck which will 90% likely be an automatic, whole bunch of harness needs to be deleted. (that ecm controls the tranny as well)

I still stick by my first opinion that you should forget efi and just throw a carb on it. Unless you are concerned about mileage, your not really going to notice a difference. Only real benifit to the CPSFI intake is efficiency. they leak causing coolant (water for boat) into the motor, the hoses to the poppets dry out and crack, fuel rail is a pain uses bubble flare fittings and sits awkwardly on the intake.

 

[Lightnig]

Re: Conversion from Carb to EFI

``EFI handles Fuel and Spark.``
umm what else is there to control in a motor? oh **** thats right it also controls combustion chamber volume in effect increasing compression.... by way of the EGR valve..........
.

Ummm, sorry, not even close.

If modern 4 cycle engines, the Exhaust Gas Recirculation (EGR) valve allows small amounts of exhaust gas to mix with the intake charge prior to entering the combustion chamber.

There is no effect on combustion chamber size what so ever. The only way EGR could affect dynamic compression is by the sole fact that allowing E.G. to enter the intake path heats the AF mix and makes it less dense, but actually cools the combustion temp. This in no way affects static compression ratio which is a simple mathematical formula which is total cylinder volume at BDC divided by total cylinder volume at TDC. There is absolutely no spot in the formula to plug in a value for EGR? yes/no...


EGR has no other function than emissions control, period.

 

[ryendube]

Re: Conversion from Carb to EFI

Ummm, sorry, not even close.

If modern 4 cycle engines, the Exhaust Gas Recirculation (EGR) valve allows small amounts of exhaust gas to mix with the intake charge prior to entering the combustion chamber.

There is no effect on combustion chamber size what so ever. The only way EGR could affect dynamic compression is by the sole fact that allowing E.G. to enter the intake path heats the AF mix and makes it less dense, but actually cools the combustion temp. This in no way affects static compression ratio which is a simple mathematical formula which is total cylinder volume at BDC divided by total cylinder volume at TDC. There is absolutely no spot in the formula to plug in a value for EGR? yes/no...


EGR has no other function than emissions control, period.

i idnt say that was the function of the egr. I realize it is used not to cool the combustion temp but to reduce the peak combustion temp. reducing the creation of N0x. it does more than this but im not here to argue i simply started responding to this thread to help a guy who didnt realize the difference in the different vortec motors, i explained them and why there better and gave my educated opinion on that keeping it cpi will be more hassle and making it a carb simplyfies it.

my comment on combustion size is this. you are adding an inert gas to the mix, it takes up space yes? where is it taking up space?
you are talking about a 62cc chamber. the difference of a couple ccs makes a difference.. do the math.

reading back i worded that previous post extremly poorly the reason I said that comment is cause previous poster is simplyfying components, im pointing out they have other impacts on the motor that most neglect. every sensor on that motor effects fuel delivery and timing. right from the speed sensor to the O2s to the air temp sensor.