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article details
Author Jeff Palmer
Categories All Honda/Acura, Prelude
Create Date September 15, 1998 00:00
Last Update April 26, 2002 20:17
Field SFC VTEC Controller -

Field SFC-VTEC Controller
Updated 9.15.98

Overview/Misc. Ramblings
Field of Japan has put together a nice little VTEC controller which does everything a VTEC controller should do, plus it adds the powerful capability of allowing the tuner to adjust fuel delivery up to 30%, in 1% increments. The fuel numbers can be set at eight points on the rpm band (1000, 2000, ... up to 8000rpms). This feature may or may not be useful to you depending upon the modifications on your motor. I have yet to fully determine exactly how the PGM-FI system operates, though it's known that the computer delivers fuel based on RPM, throttle position, O2 readings, and MAP. The SFC portion of the SFC-VTEC operates by "spoofing" MAP signals to the ECU, which in turn, causes the computer to either add or subtract fuel. One thing that remains uncertain in my mind is whether the ECU continues to rely upon the MAP signals at WOT (wide open throttle) or not. If so, the SFC would continue to affect the fuel delivery, even at WOT. Typical speed density systems (Honda uses a speed density system) ignore MAP at WOT and read the fuel straight from the fuel maps in the ROM (open loop). BUT, I have been informed by a few people that the Honda system deviates from the "norm" and continues to use MAP even at WOT, so the SFC-VTEC would presumably continue to alter the curves. Evidence supporting this is reflected in the dyno tests available below. If you happen to be a subject matter expert, please feel free to contact me (jeff@vtec.net) and give me the dirt. The other thing is that will the computer try to correct itself based on the changes it sees in the O2 sensors? In other words, if you set the SFC to increase the fuel by 10%, it will alter the MAP signals to the ECU, which will in turn increase the duty cycle of the injectors, which will richen the mixture, which will cause the voltage on the O2 sensor to increase, which will theoretically cause the computer to recalibrate itself and decrease the injector duty cycle again. There's no proof of this, but it's something that needs to be answered. So many questions, so few answers...
Features of the Field SFC-VTEC Controller
  • 1/4 DIN Size
  • VTEC Controller allows setting of VTEC transition point anywhere from 2000 to 8500 rpms, with 100 rpm resolution
  • 8-Step Simple Fuel Controller allows 30% adjustment of fuel delivery (with 1% resolution) at 1000 rpm increments from 1000-8000 rpms.
  • Realtime RPM display
  • Realtime vehicle speed display (km/hr)
  • Adjustable RPM alert (shift warning)
  • Speed Limiter Bypass (really only useful in Japan, where top speed is limited to around 112mph on most cars)
Product Performance
(4.14.98) - The above Excel charts plot the gains/losses of the Field SFC VTEC unit. The plots compare the baseline 3rd gear run on February 6th to the optimally tuned 3rd gear run with the SFC-VTEC (this is the run shown in Scenario #5 on the dyno page)
(2.6.98) Click here to view the results of today's dyno session.
The Numbers
Retail Price (U.S.)$450
Measured Gains13.4hp@4960 rpms,
-0.6hp peak
14.2lb-ft@4950 rpms
+2.5lb-ft peak
Performance Index*2.98

Optimal Settings*
VTEC Transition Point4200-4400 RPMs
Fuel Settings
* These settings are for a mostly stock H22A4 motor - they will likely differ for other applications

Basic Operating Instructions
The buttons - There are 3 important buttons - the mode select button, and the two arrow buttons.

The Operating Modes
You have 3 modes for the SFC-VTEC display:
1. SFC - simple fuel control - display shows realtime fuel % vs rpm
2. VTC - VTEC controller - display shows realtime RPMS
3. Speed - realtime speed in km/hr

  • Pressing and holding the mode button for a few seconds (until you hear a beep) changes between the modes
  • Pressing the mode button quickly gets you into an 'edit mode' for 1. & 2. there is no edit mode for 3.

Mode 1 - SFC

Clicking the mode button increments the rpm settings from 1k through 8k. You'll see something like 4 - 1 on the display. In this example, 4 is the integer value of the fuel percentage added or subtracted and 1 is the rpms in 1000's. You'll know if it's plus or minus (rich or lean) by the "+" and "-" LEDs on the left side of the display window. Once you've set the fuel settings, on the display you can monitor in realtime the exact percentage by which the fuel curve is being altered by the SFC at any given rpm (how's that for a run-on sentence!).

Mode 2 - VTC

Remember, to change modes, you have to press and hold the 'Mode' button. Once you are in Mode 2, clicking the mode button (quickly) first gets you into the VTC sub-mode, where you set the x-over point for VTEC. it should say something like 4400-H. Clicking the mode button a second time (before the edit mode times out), you can set the RPM beeper. It'll say something like 7500-b, indicating where you want the rpm beeper to sound off.

* Be careful, because if you hit the mode button while the display is in mode 2, and your engine is at any rpm besides idle, the VTEC x-over point will instantly be set to whatever rpm the engine happened to be at. So if you're loafing along at 2500 rpms in 5th (~50mph) and you bump the button, you will have mistakenly reset your vtec transition point to 2500 rpms.

Mode 3 - Speed

This is pretty much worthless, unless you want to see how inaccurate your speedo is in Km/hr. There are no user-inputs in this mode. Pressing the mode button will switch you back to Mode 1.

Installation of the Field SFC VTEC is quite easy, especially if the following apply:
  • You've installed stereo or alarm equipment in the past
  • You don't mind cutting wires in the factory wiring harness. This one sort of gave me the willies, but I haven't had any problems
  • You're handy with a crimp tool, and you have a relatively good quality crimping tool available to you. I had to buy a better one from Pep Boys. The Radio Shack crimpers that I had really sucked and would not properly crimp the connectors to the freshly cut ECU wires.
  • You can read Japanese. The manual comes printed only in Japanese. But the diagram below actually tells you all you need to know.

Quick Installation Instructions
  • Pop off the passenger side kick panel
  • In the upper right corner of the floorboard, you will see a tab of sheet metal which holds the carpeting in place. Pull the carpeting back from here and fold it back at an angle towards the center and rear of the car.
  • At this point the ECU should be exposed - actually, the piece of sheetmetal that the ECUs are mounted to will be exposed. The ECU mounting board is held in place by four 10mm nuts. Using a 10mm socket and an extension, carefully remove these nuts. Removing the nuts is easy, but it's a little tricky when you want to put them back on later.
  • Once these nuts are off, carefully lift the ECU assembly off of the 4 bolts that are holding it in place. Lift from the bottom first, and while lifting it out of place, detach all of the wiring harnesses that are connected. Place the ECU assembly somewhere safe and out of the way while you work on the wiring harness.

  • The three harnesses you will be crimping into
    (View of the passenger footwell)
  • Using the diagram above, make the proper connections from the factory ECU harness to the Field SFC-VTEC harness

  • This is what the mess of wires will look like...
  • Make sure all the crimps and connections are sound, then reconnect the factory wiring harnesses to the ECU, and bolt the ECU back in place. Be sure to connect the black wire on the SFC-VTEC harness to a proper ground
    I grounded the SFC-VTEC harness to this bolt which you will find under the passenger's kick panel With all the crimps performed, plug the 3 ECM connectors back into the ECM
  • Put the carpeting back in place and replace the passenger side kick panel. You may have to play around with the rubber trim to get it to fit properly.
  • Using the diagram above, set the dip switches on the back of the Field SFC-VTEC accordingly. They should be up-down-up-down-Clip the SFC-VTEC to it's wiring harness and take the car for a test spin to make sure it works.
  • When you determine that the unit is working properly, then you can permanently mount the SFC VTEC unit if you like. I haven't mounted mine yet, but perhaps you can put it in the DIN slot beneath the radio. So far my main concern with putting it there is that the front panel illumination of the SFC-VTEC is too bright at night, but gets washed out in bright sunlight.
Owner's Comments
From Brian David Lowry:
The installation was cake.  I have done a lot of stereo installs
and stuff and this thing was the easiest electronic component I
have ever put in a car -- easier than installing my Valentine1
with the remote display!

Everything you need comes with the unit, which is packaged very
nicely.  Tools required are a wire cutter/striper, crimper or
a needle-nosed plier, and a 10mm ratchet to get to the ECM under
the passenger-side footrest.  I recommend owning the Prelude 
Electronic Troubleshooting Manual from Helm in order to correctly
reference the necessary wires from the ECM, but this is not

All of the manuals are in Japanese, but I was able to extract enough
info to figure everything out.  I received a seperate guide outside
of the box that had a little English in it regarding the connections.
The entire install took about 30 minutes.

The unit has three modes: SFC, VTEC, and speed.

In SFC mode, you can adjust the fuel by 1% increments between +-30%
of the nominal value at every 1000 rpms.

In VTEC mode, you can adjust the VTEC "Hi-Cam" point by 100 rpm 
increments and also set a shift indicator point as well.

While driving, the modes represent a different display:

In SFC and VTEC mode, the rpms are displayed on the unit.  In speed mode
the speed is displayed (in km/h).

In all modes an LED representing "Hi-Cam" VTEC point lights up at the 
desired VTEC point, and an audible "beep" sounds at the desired shift

Another great feature is the ability to turn it off on the fly, allowing
the standard ECM settings to resume.

A note:  The engine speed is displayed according to the digital
signal from the ECM.  Thes value is a little under the value displayed
on the tach.  I assume that this is because of error in the analog 
conversion on the tach, just as the speedometer reads values a little
higher than actual.  At startup idle, the unit displays 1000, while 
the tach displays around 1100 or so.  At the redline on the tach (7400),
the unit actually reads 7100.  I do not know which is actually correct,
but I believe the Field unit more than the tach dial.

Also, the display is very bright and easy to see at night, but impossible 
during the day.  I couldn't even see that it was on as I was driving to work 
this morning.  That could have been much improved.


* Performance index is defined as horsepower gain divided by the cost, then multiplied by 100. Higher numbers are better. Keep in mind that the table above is for a very specific case. The actual performance can and will vary from system to system.

The editors of prelude.VTEC.net welcome your comments and submissions regarding VTEC Controller systems for the 5th Generation Preludes. If you have a submission to make, please e-mail jeff@vtec.net

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Date Thread Starter Thread
03-26-2010 16:57 Field SFC VTEC controller in a d16z6   (Score: 1, Normal) Wolf95
06-04-2007 19:28 sfc-vtec   (Score: 1, Normal) bealzubub88
03-11-2003 20:25 FIELD SFC FUEL/VTEC CONTROLLER   (Score: 1, Normal) wiccivic1
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