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whats the difference between CFI ecu and MPFI ecu 

 

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 Post subject: whats the difference between CFI ecu and MPFI ecu
Posted: Wed May 05, 2010 9:13 am 
Parts Gopher
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Ride: EB 91 now with mpfi

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Hey
I was just wondering why you cant run a cfi ecu in an mpfi vehicle. I ask because on CFI 2 wires (orange and green) run the injectors and on mpfi same two wires run 3 injectors each. 3 injectors common link to orange wire and 3 injectors common to green wire.
cheers
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 Post subject: Re: whats the difference between CFI ecu and MPFI ecu
Posted: Wed May 05, 2010 2:41 pm 
Getting Side Ways
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Different distributor, different sized injectors, different fuel pressure, different intake manifold, different fuel and timing maps. It may run but wont run well and is not a good idea. Surely you can shell the $10 a mpfi EA ECU is worth?

Jason
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 Post subject: Re: whats the difference between CFI ecu and MPFI ecu
Posted: Thu May 06, 2010 9:09 am 
Parts Gopher
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Ride: EB 91 now with mpfi

Location: wodonga
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yes i currently have an mpfi ecu in it, was just curious as mpfi uses all the same sensors and same pinouts so it must be seeing the same info. distributor made no difference, runs well on both, map sensor gives off same readings so no difference in manifolds as far as ecu goes, fuel pressure not controlled by ecu as far as i can tell pressure reg does that, injectors controlled in banks of 3 not 6 individually. Maybe I'm missing the point, and need to study more...and yes i did shell out the $10 for an mpfi ecu it was more of a why and how come question rather than a how can i save 10 bucks question.
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 Post subject: Re: whats the difference between CFI ecu and MPFI ecu
Posted: Thu May 06, 2010 9:56 am 
Getting Side Ways
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The distributor is different to give the MPFI ECU a 'TDC Intake Stroke' position, without this it will fire the injector on one or the other stroke and while it may run power output will not be ideal. CFI did not matter as the injector is so far from the valve the intake is full of atomised fuel anyway.

The ECU VE map is programmed to the characteristics of the intake manifold, so there is a difference.

The ECU fuel map and injector sizes are matched to the fuel pressure (i.e. you are right, the ECU does not control it, but it does need to know how much fuel a 0.5ms pulse will inject into the port).

Remember they both have different idle control solenoids also.

I suggest you read a little about ECU tuning and what is involved as you can't just assume that because two wires are the same that it will run optimally when the entire intake and fuel system is different.
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 Post subject: Re: whats the difference between CFI ecu and MPFI ecu
Posted: Thu May 06, 2010 11:34 am 
Parts Gopher
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Joined: 20th May 2009

Ride: EB 91 now with mpfi

Location: wodonga
VIC, Australia

righto, i'll get to reading some more
cheers
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