Poor man’s Power Commander: IAT Sensor modification (Intake Air Temp Sensor)

It has been posted here before but I thought that this "IAT Booster plug" info might be more accessible if re-titled and re-posted.

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", now defunct, 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.
http://www.conrad.nl/ce/nl/product/182800/NTC-temperatuursensor-Epcos-B57020M2502A0001-M-2020-40-tot-60-C-Soort-behuizing-Kunststofbehuizing-met-aansluitkab?ref=searchDetail

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

Thanks, was looking into this technique more last night. The sensor he used is out of production, but the link given still seems to work (in Dutch) and showed as in stock, and allowed me to add to basket.

I've also used the data given and technique proposed to look at equivalent sensors more widely available.

A check preliminary check found a bare probe from the same manufacturer that has a need identical curve to the one proposed initially (within 1%) and that also advertised as having a much faster response rate. Oh, at it cost £3 instead of £12.

Haven't bought yet, as I have got the money for the exhaust yet!

Just ordered a set of equivalent parts from Farnell UK. Some were so cheap (Like £1) that I got two. I also got a couple with a bigger offset to allow for more extreme mods that might require more fuel. I think his basic ones replicated a 15-20 degree offset, I've also got one at 23-25c offset, and one (or two) at 30c offset. The later should provide 10-12% more fuel! Had to order a load of random sundries to get over their minimum order level for free shipping, but they've got loads of hand tools cheap, so worth stocking up.

Oh, this is to go with a Delkevic exhaust, so I'll post results as and when.

I'll try to do some tests, and check if each sensor works. Any that do work well and are spare I will be happy to sell on to other members.

ooooh, got a dyno run booked in first thing tomorrow to get a base line! excited & nervous. Then I'll be able to make a start fitting up the exhaust and new temp probes.

Cosmic_Jumper wrote:

*** 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.

Thank you for posting this! I installed a K&N air filter when I first took delivery of my 2013 Swing. After reading your post, I decided to go back to the OEM filter and it corrected a stall/hesitation I was experiencing when accelearating wide-open-throttle. Usually if accelerating from 30 mph.
The K&N filter must be allowing too much air and causing a lean situation.

To you members that use the K&N air filter and have the same symptom as I had, replace it with the OEM paper filter. Yea, I know. Bummer! Save your engine. I guess them guys at Honda factored in the resistance the paper filter would have. This is all your choice. I would love to have kept my K&N, but I love my Swing more.

I've gone the other way. I'm currently testing several different options for NTC Thermocouples to replace the stock IAT. I've currently got a Delkevic exhaust and have de-snorkelled the stock airbox/filter. With the stock IAT the bike ran fine, but the engine & exhaust note was a bit flat. Changing to a sensor to give a 18-20 degree drop in temp seems to have made the bike more eager, but only the dyno will give true results. I've also got a 22-25 degree drop sensor, and one for a 30 degree drop. The latter is roughly 9% more fuel, so should be good for more substantial breathing work.

I plan to do a full set of dyno work with the various setups at some point.

Do the new IAT Sensor(s) fit in the same location as the OEM sensor? Can you give us any side-by-side comparison photos of the new IAT Sensors vs the OEM sensor.

Tim

The new sensors are just little electrical components about the size of a grain of rice on the end of two tiny thin wires. At present it's wired up for test use with chocolate block connectors. Once settled, I'll solder the new sensor into the loom properly and insert it into the plenum chamber via a small hole and silicon sealed in place. The original sensor will stay in place, I'll just snip the wires at a convenient spot.

Currently the test sensor is just sitting in my luggage box!

Gavin,
I wish I had half the knowledge as you do! I tried following this post, but it is way over my head. Thanks for the info about what happens to the fuel mixture when accelerating. I may even cover up the 1 inch holes I drilled out on the air filter cover. I will do more testing. Thanks again. Great forum.

I think the general gist is that the colder the bike thinks it is, the more fuel it adds to compensate for the air being denser. By tricking the bike to think it's (say) 20 degrees colder than it actually is, you can trick it into adding more fuel to compensate for mods like more open pipes or intakes.

To trick it, one needs a sensor that matches the exact behaviour of the stock probe, but offset by (say) 20 degrees colder. The issue is that the sensor is non-linear, it's output is curved you might say, hence you have to find one with the same shape curve.

Does that help?

FYI, I've got several spares, so once I've done the testing I can post some out to any one who needs one. They only cost $1-2 each, but it's tricky to find the exact ones, and most companies have a minimum order value etc. I had to make my order up to be over $35 to avoid paying a big handling & shipping fee.

gavinfdavies wrote:

I think the general gist is that the colder the bike thinks it is, the more fuel it adds to compensate for the air being denser. By tricking the bike to think it's (say) 20 degrees colder than it actually is, you can trick it into adding more fuel to compensate for mods like more open pipes or intakes.

To trick it, one needs a sensor that matches the exact behaviour of the stock probe, but offset by (say) 20 degrees colder. The issue is that the sensor is non-linear, it's output is curved you might say, hence you have to find one with the same shape curve.

Does that help?

FYI, I've got several spares, so once I've done the testing I can post some out to any one who needs one. They only cost $1-2 each, but it's tricky to find the exact ones, and most companies have a minimum order value etc. I had to make my order up to be over $35 to avoid paying a big handling & shipping fee.

Can you provide a link to the correct -20C sensor and perhaps a bit of a tutorial, please?.

I followed your instructions on the K&N mod (with standard exhaust pipe), love the improvement but I believe the micture needs richening.

Sorry for the VERY delayed reply! I sold my Swing pre covid, and then moved on to muscle cars, then off roaders. Barely ride much now.

But before I sold the Swing, I did indeed try this and it worked exceptionally well. Be it straight line drag pulls, or prolonged high speed touring (think averaging almost 90mph for over an hour).
I think I used the following probe to start with, as it was the "coldest", so added the most fuel. But it worked so well, I never tried anything else.
Anyway, hope this is of use to someone, all the best, Gavin.
Part: EPCOS B57861S0103J040
Thermistor, NTC, 10 kohm, B57861S Series, 3988 K, Through Hole, Wire Leaded