MEFI 2 with a carb
10-13-2009, 01:47 PM
#1
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MEFI 2 with a carb
One for the MEFI guys. Would it be possible to use a MEFI 2 setup on a roots blower engine w/ carbs? I was thinking of using the MEFI to control the spark curve, control idle as much as possible with adv/retard spark, and retard when knock sensor goes off. I thought I could keep everything hooked up as if EFI except for IAC, throttle position and injectors. I know this would be over kill if you had to buy the setup but I already have it.
Would this work as orginally designed or is there some controls in the computer program that would prevent this from operating.
Rick
Would this work as orginally designed or is there some controls in the computer program that would prevent this from operating.
Rick
10-13-2009, 06:45 PM
#2
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It can be made to work but it won't be easy. I worked on it before and the only time it seemed to make sense was in a class race boat that had to run a carb.
You will need to rig up a throttle position sensor to the carbs. You will need a coolant temp sensor, intake air temp sensor, knock sensor and a Mapp sensor, which are no big deal. You will need to run an efi style distributor, like the GM dual connector or an MSD 8366. About the only thing you won't need are the injectors and an IAC.
You will still have a problem with the idle. It will want to keep a steady idle at whatever is programmed. Without the IAC, you will never be able to keep the idle that steady. It is going to want to move the timing all over the place to try to maintain the desired idle speed.
If you are going to use a Mefi, I would use a 4. The 2 doesn't have a provision for boost. You will really need it to monitor the timing if you want to be able to take full advantage of the Mefi ability to control timing. For example, you can run quite a bit of timing at say 4000 rpm under light loads. However, you would want to take some out at 4000 if the engine is in boost. You need to have an ecm that can recognize the difference. You can re-pin you 2 harness to work with a 4. It takes some wiring additions to go to a 4, so it will take a few hours to do. Hope this helps.
Eddie
You will need to rig up a throttle position sensor to the carbs. You will need a coolant temp sensor, intake air temp sensor, knock sensor and a Mapp sensor, which are no big deal. You will need to run an efi style distributor, like the GM dual connector or an MSD 8366. About the only thing you won't need are the injectors and an IAC.
You will still have a problem with the idle. It will want to keep a steady idle at whatever is programmed. Without the IAC, you will never be able to keep the idle that steady. It is going to want to move the timing all over the place to try to maintain the desired idle speed.
If you are going to use a Mefi, I would use a 4. The 2 doesn't have a provision for boost. You will really need it to monitor the timing if you want to be able to take full advantage of the Mefi ability to control timing. For example, you can run quite a bit of timing at say 4000 rpm under light loads. However, you would want to take some out at 4000 if the engine is in boost. You need to have an ecm that can recognize the difference. You can re-pin you 2 harness to work with a 4. It takes some wiring additions to go to a 4, so it will take a few hours to do. Hope this helps.
Eddie
10-13-2009, 08:15 PM
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Pretty good idea you have there Eddie,
[Quote]
You will still have a problem with the idle. It will want to keep a steady idle at whatever is programmed. Without the IAC, you will never be able to keep the idle that steady. It is going to want to move the timing all over the place to try to maintain the desired idle speed.]
With the IAC controll system I would think the only thing you would need to do to make this work is to install Some kind of potentiometer to the wire harness so that you can adjust it to a set setting, Or find a self adjustable style if needed, Maybe hooked to the throttle cable area.???
http://www.wisegeek.com/what-is-a-potentiometer.htm
[Quote]
You will still have a problem with the idle. It will want to keep a steady idle at whatever is programmed. Without the IAC, you will never be able to keep the idle that steady. It is going to want to move the timing all over the place to try to maintain the desired idle speed.]
With the IAC controll system I would think the only thing you would need to do to make this work is to install Some kind of potentiometer to the wire harness so that you can adjust it to a set setting, Or find a self adjustable style if needed, Maybe hooked to the throttle cable area.???
http://www.wisegeek.com/what-is-a-potentiometer.htm
Last edited by Boat Tech; 10-13-2009 at 08:18 PM.
10-13-2009, 08:44 PM
#4
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You could actually probably use the IAC. It would probably idle better than it would without it.
You have to program a desired idle speed. With the carb, if you set the idle at 900 in neutral, when you put it in gear it may drop to 700. With efi, it would come back up to almost 900 again. The ecm will do whatever it has to do to maintain that 900 rpm idle speed.It won't be able to do it with the carb since it can't let in more air without you opening the throttle. That is where the IAC comes in. I would try to hoolk it uo and make it work.
Eddie
You have to program a desired idle speed. With the carb, if you set the idle at 900 in neutral, when you put it in gear it may drop to 700. With efi, it would come back up to almost 900 again. The ecm will do whatever it has to do to maintain that 900 rpm idle speed.It won't be able to do it with the carb since it can't let in more air without you opening the throttle. That is where the IAC comes in. I would try to hoolk it uo and make it work.
Eddie
10-14-2009, 07:30 AM
#5
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Thread Starter
Eddie,
Thanks for the reply. Why do you need the throttle position sensor if the spark is the only item you are controlling? I understand the need for it if you have the injectors, for accel/decel, clear flood, etc.
Rick
Thanks for the reply. Why do you need the throttle position sensor if the spark is the only item you are controlling? I understand the need for it if you have the injectors, for accel/decel, clear flood, etc.
Rick
10-14-2009, 12:14 PM
#6
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The ecm needs to know where the throttle is at. It will let the ecm know how much load the engine is under. It will take throttle position, Mapp, and rpm into consideration to determine what to do. It will also let the ecm know when to get out of the idle circuit, which happens at 5% throttle.
Eddie
Eddie
