SFI and MFI engines
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SFI and MFI engines
What is the difference between SFI and MFI engines?? Is it mass air and speed density, or multi port fuel injection and carbuerator or throttle body injection. I have no idea what it is. Thanks
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Joined: Jan 2002
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From: suburban atlanta
SFI and MFI engines
[updated:LAST EDITED ON 31-Jan-02 AT 09:48 AM (EST)] The difference mainly is that the injectors are fired differently. The SFI or SEFI injectors are fired much like spark plugs, immediately before (or after) the intake valve opens, for a given cylinder. The MFI or Multiport Fuel Injection system has multiple injectors, fired generally in banks or 3 or 4 on V-type engines, or in pairs in inline 4-cylinder engines, no matter what the intake valve is doing. Differentiated from a CFI or TBI-throttle body injector which just has 1 or 2 injectors mounted at the top of the throttle body, where the air/fuel are mixed there and are passed through the intake to the engine, much like a carbureted engine. Each has their costs/benefits with SEFI costing the most, and CFI costing the least.
MAF versus MAP sensor: A MAF measures how much air is going into the engine, and sez must have this much gasoline for this much air. If the air intake system has leaks, MAF will NOT know, and the engine will run like S..T. MAP just knows manifold vacuum, and figures the load on the engine from that- 0 vacuum== wide open throttle==push in a lot of fuel. 15"vacuum==at idle==shut down the fuel flow, roughly. The fuel injection numbers (flow time in msec) that a MAP system uses are pre-computed and burnt into the ROM for the ECM for a specific engine calibration. (The o2 sensor starts with that number and fudges it to get 'perfect' combustion). The MAF *knows* how much air is going in, (UNLESS there are leaks) and has a better baseline of injector pulse figures to use, and doesn't have to impute the load on the engine from the vacuum reading.
Least thats what i think.
tom
MAF versus MAP sensor: A MAF measures how much air is going into the engine, and sez must have this much gasoline for this much air. If the air intake system has leaks, MAF will NOT know, and the engine will run like S..T. MAP just knows manifold vacuum, and figures the load on the engine from that- 0 vacuum== wide open throttle==push in a lot of fuel. 15"vacuum==at idle==shut down the fuel flow, roughly. The fuel injection numbers (flow time in msec) that a MAP system uses are pre-computed and burnt into the ROM for the ECM for a specific engine calibration. (The o2 sensor starts with that number and fudges it to get 'perfect' combustion). The MAF *knows* how much air is going in, (UNLESS there are leaks) and has a better baseline of injector pulse figures to use, and doesn't have to impute the load on the engine from the vacuum reading.
Least thats what i think.
tom
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From: Cullman Alabama
SFI and MFI engines
[updated:LAST EDITED ON 31-Jan-02 AT 08:21 PM (EST)]
What an answer!!! I'm impressed.
Tomw, you should come up with a Kit. A list of stuff to take off some engine, so we could plagerize this 'newer' engine to make our 'older' engines more fuel efficient, and environmentallly friendly.
It shouldn't be real difficult to make our old Six bangers into the svelt smooth performers those V-6's are!
Maybe a Kit like that would hold off Malicious S..t like SB 1766!
What an answer!!! I'm impressed.Tomw, you should come up with a Kit. A list of stuff to take off some engine, so we could plagerize this 'newer' engine to make our 'older' engines more fuel efficient, and environmentallly friendly.
It shouldn't be real difficult to make our old Six bangers into the svelt smooth performers those V-6's are!
Maybe a Kit like that would hold off Malicious S..t like SB 1766!
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