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AF Newbie
Join Date: Sep 2004
Location: santo Domingo
Posts: 99
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can some1 please check this out and tell how true it is and how it aplies to integras
NTPOG 5th Gen Air/Fuel Controller - OBD2 "Workaround"
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Author: Todd Marcucci
Why?
There has been much debate over how OBD2 ('96 and up Preludes) works and what it does. What is known to the tuning world from dyno plots and tuning is that the ECU on OBD2- equipped vehicles will eventually "detune" modifications that alter cam timing, ignition timing, and air/fuel delivery. This includes common breathing modifications (intake/header/exhaust and port work). What this means for the average tuner is that when you bolt on i/h/e, do manifold or head (port) work, change injectors or fuel pressure, or just about any other engine-related mod, the ECU will detect the change in emissions and alter the timing and fuel maps to compensate. This has been dyno proven on multiple occasions with multiple different performance mods. It also happens that this is especially true for air/fuel controllers (AFCs).
The purpose of the EPA-mandated OBD standard was to provide a means for which factory engine controls could diagnose engine control malfunctions and identify to the driver (and subsequently the repair shop) that there was a problem. The OBD2 standard, mandated for all 1996 and up vehicles, required that the OBD interface be standardized across all makes and models, as well as monitoring emissions components performance and proper operation. This means that for 1996 and newer vehicles with OBD2 that if you remove the catalytic converter or EGR valve that the ECU will eventually identify that these components are no longer working and flag a check engine light (CEL) and OBD2 code.
Aside from OBD2 (including original OBD vehicles), Honda ECUs (from the factory) run rich at WOT and in VTEC. This is likely for safety's sake, to help reduce the chance of detonation and allow for wide variances in climate, altitude, temperatures, etc. This can have a drastic effect on power. Honda ECUs also don't deal very well with bolt-on mods due to the MAP-based system of determining airflow into the engine. What this boils down to is that whether you are stock or modified, you are probably running too rich at WOT and in VTEC. At part throttle, it is debatable that an AFC gains much if anything at all- the engine is running "closed loop" (using the O2 sensor to trim the fuel mixture) and Hondas are tuned to run lean at part throttle for clean emissions.
The Fix
There are several ways to fix this problem. The first would be to do an OBD1 "conversion" where you replace the stock ECU with an older one from the '93-'95 Prelude. This has its own drawbacks, requiring you to find/buy an ECU, a conversion harness (or making your own), etc. Even more expensive and time consuming would be to switch to a standalone system from Motech, AEM/GEMS, Haltech, etc.
While any of these would certainly be desireable and provide you with other options (such as programmability), there is a much cheaper and easier solution. Knowing that the OBD2 ECU will eventually learn and "detune" what you are working to achieve, the real objective here is to insure that your computer doesn't learn, or more accurately, "forgets" what it learns. What we will cover here is interrupting the backup power to the ECU to make sure that it does not retain it's memory while the car is off. It will "detune" while you are driving but go back to a clean slate every time you shut the engine off. Also, since the EGR and catalytic converter malfunctions are stored and only "flagged" as a problem after multiple driving cycles, these will be reset each time you start the car. This means you can install a test pipe (provided the second O2 sensor is still installed) or block off the EGR valve (or remove it) and not have to worry about a CEL. Not a perfect method, but a LOT cheaper, easier, and almost as effective as any other option.
What we will be doing here is installing a switch on the backup power line to the ECU that will allow you to turn "on" or "off" the memory function of the ECU. Please note that this mod is effectively the same as pulling the 7.5A CLOCK/RADIO fuse from the under-hood fuse panel, or removing the battery cable (all of which reset the ECU). The beauty of this mod is that you don't have to pull a fuse each time you shut the car down, and you don't reset the clock and radio (requiring you to re-enter the security code). If you are VERY worried about tearing into the stock wiring, you may want to just pull the fuse weekly, which is about as "fast" as the ECU learns (a few hundred miles).
WARNING!
Unless you have a custom harness installed for a Field or Apex'i air/fuel controller, this modification requires you to hack your stock wiring! This will under ALL circumstances void your factory warranty! Neither NTPOG nor the author is responsible for your voiding of the warranty or any problems that might result. Be sure to solder and heat shrink all connections. Keep in mind that returning your car to stock will require, at the least, cutting and re-splicing all the connections you make here. Leave enough wire to do this if you ever plan on reversing this mod. In other words, do your work well the first time!
What You Need
- SPST toggle switch (available at Radio Shack)
- 18 gauge stranded hookup wire (available at Radio Shack)
- Wire strippers/cutters
- Heat shrink tubing (available at Radio Shack)
- Soldering iron and solder
- Electrical tape
- 10mm socket, ratchet, and 6" (or more) extension
Removing the ECU
Since we've already covered ECU removal, we won't cover it again. Please see the Wiring page for the steps on how to remove it. Once you remove it and have the wiring exposed, you should see something like this:
Wiring
The wire that you want is C10. Looking at the ECU, this is the wire on the far right, top row, of the center connector. This is looking *into* the ECU, or into the back of the connector that plugs into it (the wire side). The wire is white with a yellow stripe and a gold dot. Note: This color code applies to '96 and up Preludes only. Other models/years may vary.
Cut the wire a few inches back from the connector (so you have room to solder to the ECU side of the wire):
Now solder the switch in series with this wire like so:
Pretty much any switch will work, provided you know how to wire it as SPST. For most switches whichever end the toggle is flipped towards, those contacts are OPEN. The other contacts (facing away) will be shorted (ON). Flipping the switch alters the on/off state of each of the sets of contacts. Pick two contacts and wire them to the ECU- just be sure you know when they are shorted and when they are not, based on the position of the toggle!
This will setup will allow you to keep the switch OFF (open the backup power circuit) to keep the ECU from "remembering" anything. If you get a CEL, throw the switch back to the ON position and then it will remember the code. Just be sure you mark or know what's ON and OFF for your particular switch and wiring. By hiding the switch, this should also allow you to return the car to the dealer "acting normal." Most dealers don't like it when they can't retrieve diagnostics info!
In response to MANY inquiries about this mod, this has been running for quite some time on various cars in NTPOG and elsewhere with no reported problems. So far there have been no reported issues with fuel economy or other problems. There is no need to let your car idle for any period of time or anything else- just get in your car and drive off. It will act like normal and drive like normal, you will never know the switch is there or on or off (so know how you installed it!).
If you're installing an AFC, continue on with Programming your Air/Fuel Controller.
extracted from
http://www.ntpog.org/mods/fifth-afc/ecu.shtml
i know its for preludes but other hondas are also OBDII
and im starting to think it is tru cause i have an 99 GSR with basics I/H/E and i can only make 15 MPGcity. i bough it with the mods so can compare to stock
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