EFI OFAB & OFAC differences are a internet myth - discus

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EFI OFAB & OFAC differences are a internet myth - discus

Postby DavidBolton on Sat Jan 10, 2004 12:19 pm

Seems to me that the differences between OFAB and OFAC are pretty much a internet s**t myth!

They are both under the same wiring diagram in the Haynes manual and there isnt much documentation about the two either. It looks like the OFAC was just an upgrade to the OFAB in the same way that the Escort Turbo has 3 different ECU's which all work the same but have slight differences - ie the knock sensor.

The slight differences between the OFAB & OFAC are:

Pin 8 or 27 - CO Signal
Different connector for the map sensor
Different map sensor

Pin 45 is the same on both and apart from this there are no differences! So people are right when they say you must match a OFAB ECU and Map sensor & you must match a OFAC ECU and Map sensor but everything else including the wiring looms are interchangable.

Discuss and lets see if we can sort this out once and for all!

Dave.
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Postby RS TURBO S2 on Sat Jan 10, 2004 12:52 pm

haveing looked my self at the wiring diagrams i cant see much differances other than like you say with the map sensors which as mention elsewhere a very different in that ofab is voltage type like cossies etc and the ofac is frequancy type like used on efi xr's but with a greater pressure range.

i have an efi loom from an xr2i to convert origionally to ofac but i now want ofab due to being able to run the 3 bar map sensor for greater boost. but having found info on loom changes from efi to ofac turbo i couldn't find an for ofab ecu, so after looking at the diagrams i cant find much in between ofac and ofab.

next opinion please..... :-?
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Postby DavidBolton on Sat Jan 10, 2004 12:59 pm

The XR2i loom uses the right connector for the OFAC map sensor so you could use that ok. To use the OFAB map sensor just chop off the connector and wire in the OFAB style connector! Check the location of Pin 7/28 and select your ecu.

Dave.
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Postby Stoned on Sat Jan 10, 2004 1:05 pm

bottom line is 0FAB lets you run more boost and may be slightly less economical

end of discussion
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Postby RS TURBO S2 on Sat Jan 10, 2004 1:06 pm

the main problem i find with wiring looms is colour changes to the wires like when ford change from 1 manufacturer to another for the speedo like changing the fuel and temp guages round pointless unless they are setting out to confuse us mad modders...

ultimatly i will go for an aftermarket management on my car but i need efi to map it better thn the old mfi kak and aint the money for pectel or wot ever cossie stuff is ok but expensive by comparison to festa turbo stuff and not that much better in terms of mapping and reliability on a car with say 250 bhp.
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Postby RS TURBO S2 on Sat Jan 10, 2004 1:08 pm

Stoned wrote:...... more boost and may be slightly less economical



if we cared about fuel economy would we drive these cars??? :wink:
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Postby DavidBolton on Sat Jan 10, 2004 1:38 pm

Stoned wrote:bottom line is 0FAB lets you run more boost and may be slightly less economical

end of discussion


I know mate thats why I have OFAB but Im not talking about which system is best at the moment, simply the workings of both systems!

I lot of people still go OFAC because they arent looking to run high boost and parts are easier to get, like the 3 ecu's on ebay at the moment!

Dave.
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Postby RS TURBO S2 on Sat Jan 10, 2004 1:49 pm

dave you say ofac is easier to get hold of your right about the ecu but trying to get a map sensor for the ofac is like trying to look cool in a nova



imposible



what does seperate them is down to the workings of the map sensor from wot i here, the ofac frequancy type is much more precise and acurate than the ofab voltage affair, maybe why the ofac's have better fuel economy,, i dunno. but this is all around the time of emissions this n that so maybe ford changed to ofac to lower the emisions for gov figues

any thoughts??
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Postby DavidBolton on Sat Jan 10, 2004 1:55 pm

Didnt know it was hard to get a OFAC map sensor, never tried though! :lol:

Yeah I'd agree that it sounds like the OFAC works better and is more precise. I bet most people who go OFAB because they want to run high boost probably never do as 1 bar is normally enough for most people!

Dave.
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OFAC

Postby MIK3Y on Sat Jan 10, 2004 1:57 pm

Mine is OFAC and seems to idle rev slightly lower than 2 OFAB FRSTs ive been in despite adjusting the screw, so maybe this is the only way OFAC reduces emissions???
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Postby MIK3Y on Sat Jan 10, 2004 2:01 pm

Also both having 2 bar map sensors as standard does this mean it can gauge up to 2 bar of boost (28psi) or only 1 bar (14psi) of boost and 1 bar of vacum as ive read somewhere? Thanx

Thus meaning id hav to go OFAB and get a 3-bar map sensor to run more than 14psi?
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Postby RS TURBO S2 on Sat Jan 10, 2004 2:17 pm

yes m8 thats right a two bar sensor measure 1 bar negative (vacumm like off boost yeah?) and 1 bar positive pressure (14.5 psi)

so basically a 2 bar will go to 14 psi acuratly and a 3 bar to 28 psi and so on i have seen a 5 bar map sensor somewhere :oooh:
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Postby DavidBolton on Sat Jan 10, 2004 2:36 pm

You get the 2.5 as well remember, thats what im planing to run! -1 +1.5

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Postby RS TURBO S2 on Sat Jan 10, 2004 2:41 pm

yeah dave the 2.5 is the ofac one ?? is that right so should see 21 psi which is high enuff for most .. but i will run 28 psi for 1/4 miles or down the odd home straight on track days, thats if my 3 stage system works :-?
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Postby DavidBolton on Sat Jan 10, 2004 3:13 pm

OFAC is still 2 (-1 +1) the 2.5 is cossie!

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Postby beanyfrst on Sat Jan 10, 2004 3:23 pm

ok ive not had no sleep all night so forgive me if i missed on something but,how can you tell if its ofab and ofac that you have got
Has bought my Fiesta RS Turbo back, Needs a lot of TLC
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Postby RS TURBO S2 on Sat Jan 10, 2004 4:29 pm

Go to search and search for ofab. Someone has asked this question before to which Gadget replied to showing pictures of the two different types of map sensor. Also you can look at the ECU - where the multi plug plugs in it says either ofac or ofab.


AHH yes that's right 2.5bar is escort cossie!!
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Postby oriont on Sat Jan 10, 2004 4:49 pm

mines running ofac and peaks at 23psi and holds 21psi.
thanks
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Postby RS TURBO S2 on Sat Jan 10, 2004 5:13 pm

oriont wrote:mines running ofac and peaks at 23psi and holds 21psi.
thanks
oriont :D


yeah have herd that this is fine especially on ofac stuff but the map sensor is not as acurate with boosts over its intended design parameters.
doesn't mean it wont work just that it may say there is only 20 psi when there is 24 and thus the ecu will only fuel accordingly with this reading.

this is only what i have been told by the way
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Postby Project on Sat Jan 10, 2004 6:09 pm

DavidBolton wrote:OFAC is still 2 (-1 +1) the 2.5 is cossie!

Dave.


Errr, are you sure about that one?!
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Postby oriont on Sat Jan 10, 2004 6:25 pm

the map sensor is not as acurate with boosts over its intended design parameters.
doesn't mean it wont work just that it may say there is only 20 psi when there is 24 and thus the ecu will only fuel accordingly with this reading.


this is true but mine has been mapped by msd and has a box of tricks fitted to the map sensor wiring to smooth out signal :)

thanks
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Postby RS TURBO S2 on Sat Jan 10, 2004 7:31 pm

oh i c the old box of trick trick eh?

dont think it works on the other map sensors does it??

only ofac type
???

just a geuss
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Postby Excursion on Sat Jan 10, 2004 7:43 pm

Alan Fibblesnork wrote:
DavidBolton wrote:OFAC is still 2 (-1 +1) the 2.5 is cossie!

Dave.


Errr, are you sure about that one?!


Yeah OFAC is 2.5 isnt it, OFAB is 2 but can be replaced with a 3.
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Postby Rolls on Sat Jan 10, 2004 9:20 pm

dont the 2 map sensors work on diff principles- one is a digital, and one is analogue?- remeber stu saying something about em on PF?
hi btw dave- hows the car coming?
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Postby DavidBolton on Sat Jan 10, 2004 10:32 pm

Its excellent cheers Rolls, I just wish I could get some pics of the thing!

I dont have access to a digi camera! I have some pics on my phone but I need a blue tooth adapter for my pc to get them from the phone to my pc.

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Postby James-UK on Sun Jan 11, 2004 5:26 pm

DavidBolton wrote:thats what im planing to run!
Dave.


Still not started then Dave?
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Postby DavidBolton on Sun Jan 11, 2004 7:40 pm

James-UK wrote:Still not started then Dave?


Running standard ofab map at the moment, thanks for asking.

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the truth

Postby boost master on Tue Feb 03, 2004 11:21 pm

OFAB : - used in ERST managment, open an ecu and you will see the small pcb on spacers isolated from the ecu, (in other words there the same) used sign wave (voltage levels + and - 5 volts) to signal the processor on the main board (ecu) to drive the injectors.


OFAC : - uses binary 0s and 1s to signal the processor in the ecu that drives the injectors to vary there on and off time. Think I was told that this was changed due to noise levels on the signaling.

Ahmed bayjoo gave me this intresting info, thought I would share for those who maybe intrested.
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Postby beanyfrst on Wed Feb 04, 2004 1:11 pm

I have ofab woo-hoo
Has bought my Fiesta RS Turbo back, Needs a lot of TLC
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Re: EFI OFAB & OFAC differences are a internet myth - discus

Postby Fraggle on Mon Jun 13, 2011 3:20 pm

Sooooooooooooo this debate still rumbles on,,not on this thread though :lol: untill now....

Found this http://passionford.com/forum/pictures-v ... urbos.html

the first post is all im interested in...20psi :o ..i thought standard management was supposedly s**t an no-one wants to map it anymore [ERRR] according to the bs on net its old hat an cant do much with it???

Reason i bought this up is im lookin at standard ecu's on skip bay an some are rather cheap..Gotta be fecked?...But i've become rather interested in all things electrical..eg pcb circuit design/layout/REPAIR..But i Cant find any FMC original circuit design/layout schemetics of how these ecu's were designed or what parts are used in em...?

Seen a Niche i wanna possibly fill :wink: :lol:

Anyone know how or where to possibly obtain such Data as someone designed the ECU's internal circuitry so original design Blueprints must be about somewhere?

:D
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Re: EFI OFAB & OFAC differences are a internet myth - discus

Postby Excursion on Mon Jun 13, 2011 4:25 pm

The yanks have spent a lot of time on EECIV and knew the system inside out about 20 years ago. There is loads of info out there.

Both OFAC and OFAB can run 20psi, but not particularly well. The OFAC MAP sensor is a frequency type and offers more accurate control, but has a limitation.

A mapper can go beyond the limit but accuracy goes out of the window.

The systems are good for a standard-ish car, but you are better off with something like MS if you want to start going beyond.
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Re: EFI OFAB & OFAC differences are a internet myth - discus

Postby Fraggle on Mon Jun 13, 2011 5:13 pm

Excursion wrote:The yanks have spent a lot of time on EECIV and knew the system inside out about 20 years ago. There is loads of info out there.

Both OFAC and OFAB can run 20psi, but not particularly well. The OFAC MAP sensor is a frequency type and offers more accurate control, but has a limitation.

A mapper can go beyond the limit but accuracy goes out of the window.

The systems are good for a standard-ish car, but you are better off with something like MS if you want to start going beyond.


Cheers fella...Was more lookin at the original design of the system....Like i say im trying to find if at all pos the original "CAD" if you will,,circuit layout diagrams/Bueprints for the circuit board itself..components list that stuff...
If that makes sense :-?
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Re: EFI OFAB & OFAC differences are a internet myth - discus

Postby Excursion on Mon Jun 13, 2011 6:07 pm

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Re: EFI OFAB & OFAC differences are a internet myth - discus

Postby Fraggle on Mon Jun 13, 2011 7:14 pm

legend,,
thats the stuff im lookin for...
where can i find them fella?...also is there a component makeup/id list/diagrams available?
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Re: EFI OFAB & OFAC differences are a internet myth - discus

Postby andymac on Mon Jun 13, 2011 8:47 pm

PWM for the pressure transducer would be more accurate as you're only looking for rising / falling edges at the ECU end - the amplitude doesn't matter so long as there's enough deviation to trigger upon. Since the electrical characteristics of the loom change with time of year and age this system can only be described as a Good Thing. This would also make for less complicated code and use less resources on the ECU itself (you're just counting timings as opposed to requiring a historically expensive A/D converter). Also means less points of failure, another Good Thing.

The problem is that there's almost certainly not "room" in the ECU for the additional calibration data needed for a high pressure system (plus the transducer probably has limited resolution at the upper limits - you'd be pushing what the hardware can do at either end) which would limit what you could do with the ECU without losing map resolution.

Also seems to me that it would be a straightforward thing to build a PWM generator off the back of an A/D to allow you to run your own choice of MAP sensor; getting hold of the timing data and knowing if the A/D sample time would be acceptable for rapidly changing boost levels is quite another matter though.

OTOH I could be talking nutsack.

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