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 Enriching Fuel mixture: IAT Hacking

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PostSubject: Enriching Fuel mixture: IAT Hacking   Wed Jun 14, 2017 10:32 pm

Further to Lloyd193's earlier post regarding hacking the engine coolant temperature (ECT) sensor to enrich the fuel mixture is this post detailing hacking the IAT sensor from "another" Silverwing forum:

- By Dutchwing Date 2014-03-12 05:12

It was time to do some big maintenance on my FJS600A 2007 with 23.000km. I live in The Netherlands and the Honda Dealer is so expensive that even with buying some extra tools (like torque wrench etc.) it's cheaper to do everything myself... Also ordering parts online (especially in Italy) saves a lot of money.

List of what has been done:

[Edit: What followed then was a long list of various standard maintenance and upgrades the OP performed]

But what was really necessary and is not really well documented for this motor scooter: installed home brew IAT modification!

*** Note: When the complete exhaust is exchanged with a wide pipe exhaust without catalyst converter AND the "open" K&N air filter is installed the air-fuel mixture gets too lean during acceleration. For continued closed loop operation with the O2 sensor it's fine because the lean mixture will be compensated by the ECU but during acceleration the ECU works open loop and will be too lean. That's why I decided to think out-of-the-box and come up with a solution for that.

On the internet numerous articles can be found about "tuning boxes" that "modify" the signal from the IAT. Basically, the IAT is just a simple NTC resistor and it has a certain characteristic. If some other resistance is put in series with the IAT sensor the total resistance will be higher and the ECU thinks the temperature is colder. However, just adding a fixed resistor does not work because the curve is not linear. Some tuning boxes have internal "compensation" for that and lots of other claims but in the end the ECU just needs to be tricked to "see" a 20 degrees Celsius colder air than what it is in reality. This will add approximately 6% fuel to the mixture. So why putting a +$150 box in series with a cheap temperature sensor instead of just replacing the cheap sensor itself? So I took out the original Honda IAT and measured its curve (put it in the fridge with -18C, 0C, in water of 10, 20, 30, 40 and 50C and had Excel draw a nice curve through the dots. Then I shifted the curve by 20C and got a much steeper curve to fit the new NTC in. Comparing the curves of numerous commercially available NTCs I found one that pretty well fits and the best feature of it is that it's an ordinary NTC that is also used in airco systems and it comes in a nice sturdy plastic molded housing. The price is around 12 euro so a bit more expensive than an ordinary NTC but this one really fits well. The size of the housing is 8mm round and that's exact the size of the original sensor. So I drilled the original sensor out with an 8 mm drill and glued the new one in so I could use the old sensor housing as mount for the 2 screws. Connected the wires with soldering and some crimp-tube and that was it!

Result of this is that the engine now runs very well, no more "lean fuel" hesitation and in combination with the K&N filter and "street legal" Laser exhaust with added O2 sensor it's really fun to drive. Reaction on quick throttle changes used to be a bit tame, now it's much more aggressive and really wants to accelerate.
Even with a passenger it easily tops +180Km/h on the speeddial without hesitation and with a new belt, while the rpms are even a bit lower due to the new belt. Of course the JCosta helps a lot too...

For those who would like to get rid of the lean mixture, the NTC I used is the Epcos B57020M2502A0001 and it's relatively easy to replace. The deviation is small, aim is -20C in the range between 0 and 40C and it does -14C at outside temp of 0C and 19C at outside temp of 40C (hence between 14 and 21C under outside temperature). So the enrichment gets a little more at higher temperatures which is nice to keep the engine cooler in a hot summer. Note you won't see a noticable fuel consumption change. The enrichment of max 6% is only active during acceleration. During constant speeds the ECU works with the lambda (O2) sensor in closed loop mode. In case the NTC is disconnected an error will be logged by the ECU and internally it will work with a fixed value that corresponds with 25C.

Temp C  Original  EPCOS 5K
-20  22853  48614
-15  17272  36503
-10  13054  27680
-5  9866  21166
0  7456  16330
5  5635  12696
10  4259  9951
15  3219  7854
20  2432  6246
25  1838  5000
30  1389  4028
35  1050  3266
40  793  2664
45  599  2185
50  453  1803
55  342  1495
60  259  1246
65  195  1044
70  147  878

Last edited by Cosmic_Jumper on Fri Jun 16, 2017 4:03 pm; edited 1 time in total (Reason for editing : Content)
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Maxi-Scooter Rider
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PostSubject: Re: Enriching Fuel mixture: IAT Hacking   Thu Jun 15, 2017 1:50 pm

Wow  scratch
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Silver Wing Expert
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PostSubject: Re: Enriching Fuel mixture: IAT Hacking   Thu Jun 15, 2017 5:27 pm

Huh ?? Question
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Site Admin

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PostSubject: Re: Enriching Fuel mixture: IAT Hacking   Thu Jun 15, 2017 5:50 pm

Yeah guys, it's a pretty long post, a lot of which is not to the point, but I figured that I'd post it in its entirety. Actually the meat of the post is pretty good technical information.

And again, it's more so intended for we who can't leave well enough alone.  

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Enriching Fuel mixture: IAT Hacking
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