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Discussion Starter #1
I've gone through and done a bit of research on all the tuning options for my 2020 Grom SF.

I'm a bit confused with the Yuminashi ECU versus the ECU reflash thorugh.

So reading through the forums, the Yuminashi ECU is a Keihin MSX ECU. For this ECU, the selling point is that it is self-adjusting. I would have thought that the stock ECU was somewhat self-adjusting like with a car's ECU. But from what I'm reading, the OEM/Factory ECU doesn't seem to be able to compensate very much. I read somewhere that the OEM/Factory ECU is a Keihin as well.

1. Is the Yuminashi ECU a different Keihin ECU?
2. Did they just enable the auto-tuning function in the OEM/Factory ECU?
3. Did the USA just get a different Keihin ECU that doesn't adjust much?

Also I read that the cold-start (dependent on oil temperature) is disabled.

4. What does cold-start on the grom actually do? Someone said that a solenoid stays closed due to this being disabled?

Now with the ECU Reflash like CJR and DHM...They're just taking the OEM/Factory ECU and flashing a new tune on.

5. Does this new tune not have the auto-tuning due to the OEM/Factory ECU not having an auto-tune function?

Which brings up the comparison...

6. Does the Yuminashi ECU auto-tune work well for a broad range of things... while the reflash works awesome for specific things? Like the reflash is super optimized for the mods you have while the Yuminashi is just able to auto-tune to optimized levels?

Tried searching on Facebook and this forum but didn't really find anything on this. Thanks again guys!
 

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There is no autotune function on the OEM ECU. There is STFT and LTFT but given the single-wire O2 sensor, it isn't terribly accurate until the engine gets really hot, and even then, it's only great at maintaining 1.0 lambda.

I do not personally know what the Yumi ECU is, but I'm sure you can figure it out with some digging.

It took me a couple hours to figure out their 32 mm Grom throttle is just a machined CB150R StreetFire (old model, K15) throttle made by Keihin. p/n 16400-K15-902

...unrelated but it just gives you an idea of where they're sourcing stuff - ~150cc Indonesian race bikes commonly use this throttle because it's simple and easy to bore to 32-33 mm.
 

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Discussion Starter #3
There is no autotune function on the OEM ECU. There is STFT and LTFT but given the single-wire O2 sensor, it isn't terribly accurate until the engine gets really hot, and even then, it's only great at maintaining 1.0 lambda.

I do not personally know what the Yumi ECU is, but I'm sure you can figure it out with some digging.

It took me a couple hours to figure out their 32 mm Grom throttle is just a machined CB150R StreetFire (old model, K15) throttle made by Keihin. p/n 16400-K15-902

...unrelated but it just gives you an idea of where they're sourcing stuff - ~150cc Indonesian race bikes commonly use this throttle because it's simple and easy to bore to 32-33 mm.
What is STFT and LTFT?

As for the ECU itself, I believe it's a Keihin ECU and according to the link below, it's a MSX ecu (vs Finbro that uses a cb150R ecu).


But yeah the throttle body thing makes sense for sure.

I guess the ultimate question for me is really:

Since I am not close to CJR or DHM, I'd get an "off the shelf" tune for intake/exhaust/cam. But is there a reason that these tunes are better than an ECU that can auto-tune?
 

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What is STFT and LTFT?

As for the ECU itself, I believe it's a Keihin ECU and according to the link below, it's a MSX ecu (vs Finbro that uses a cb150R ecu).


But yeah the throttle body thing makes sense for sure.

I guess the ultimate question for me is really:

Since I am not close to CJR or DHM, I'd get an "off the shelf" tune for intake/exhaust/cam. But is there a reason that these tunes are better than an ECU that can auto-tune?
I don't know the capabilities of the Yuminashi ECU, but the "off the shelf" tune by CJR works pretty well for me:
PW= CJR
 

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What is STFT and LTFT?



Since I am not close to CJR or DHM, I'd get an "off the shelf" tune for intake/exhaust/cam. But is there a reason that these tunes are better than an ECU that can auto-tune?
Short term fuel trim and long term fuel trim.
I'd rather have an off the shelf tune for the mods I have. The yuminashi marketing implies that it can auto tune but I don't know much about that. They just sell a bunch of different sized fuel injectors and suggest which one to get for your level of mods.
 

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CJR doesn't do an "off the shelf tune". The tune is based off of the parts/modfications you are running. If they don't have a tune for your setup they will set their bike up just like yours and run it on the dyno to make you a custom tune
 

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Discussion Starter #7
So what I'm gathering is that Yuminashi has developed their own ECU in a sense. They didn't just take a factory ECU and enable auto-tune. This seems to make more sense.

I know the tunes by DHM and CJR are more like say a tune by Stratified or 5150 or other car tuning companies in which they flash a new tune on.
 

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I've gone through and done a bit of research on all the tuning options for my 2020 Grom SF.

I'm a bit confused with the Yuminashi ECU versus the ECU reflash thorugh.

So reading through the forums, the Yuminashi ECU is a Keihin MSX ECU. For this ECU, the selling point is that it is self-adjusting. I would have thought that the stock ECU was somewhat self-adjusting like with a car's ECU. But from what I'm reading, the OEM/Factory ECU doesn't seem to be able to compensate very much. I read somewhere that the OEM/Factory ECU is a Keihin as well.

1. Is the Yuminashi ECU a different Keihin ECU?
2. Did they just enable the auto-tuning function in the OEM/Factory ECU?
3. Did the USA just get a different Keihin ECU that doesn't adjust much?

Also I read that the cold-start (dependent on oil temperature) is disabled.

4. What does cold-start on the grom actually do? Someone said that a solenoid stays closed due to this being disabled?

Now with the ECU Reflash like CJR and DHM...They're just taking the OEM/Factory ECU and flashing a new tune on.

5. Does this new tune not have the auto-tuning due to the OEM/Factory ECU not having an auto-tune function?

Which brings up the comparison...

6. Does the Yuminashi ECU auto-tune work well for a broad range of things... while the reflash works awesome for specific things? Like the reflash is super optimized for the mods you have while the Yuminashi is just able to auto-tune to optimized levels?

Tried searching on Facebook and this forum but didn't really find anything on this. Thanks again guys!
Hey, I have quite a bit of knowledge on the ecu side. I do a lot of ecu flashing and tune with standalones/piggybacks etc. A lot of these parameters can be found in the PV3 software which has been great for exposing the ECU.

1. I have done testing with them and my understanding it’s an overseas MSX reflashed. They continue to use the learning portion under 80% like the USA ECU so it is still “self mapping” however over 80% appears to be a modified more aggressive than stock fuel map, that requires matching the injector to your ecu. I have not found the wide open area (80-100%) have any more learning features than our stock ECU. However with more fuel than stock in those areas, it can work with basic bolt ons okay. We are just unsure what the ecu was tuned for modification wise as it is a bit of a generic map. During my testing, the ecu would work okay, however you did have to change modifications around to suit the AFR, instead of tune the ecu to suit the modifications. I had a rich spot in the higher rpm and a lean spot down low, so I switched from a short ram intake to a mid length and actually helped shift the AFR in those areas in my favor. This can also be done with any OEM ecu and flashed ecu. I spoke with yumi on the subject and he never stated it was “full” self mapping, just that it had self mapping capabilities. I believe this was a rumor that started when comparing it to the finbro ecu.

2. The OEM ecu uses the o2 sensor to target a .602 voltage = 14.7afr under 80% throttle. Some see this as too lean although for general cruising it is good for fuel economy for stock bores. It starts learning after 54*C engine oil temp. Again, one can view a lot of parameters like that in the dynojet PV3 software.

3. As far as difference in overseas ECU to USA, the fuel maps are a little different. I haven’t compared them much side by side as we flash over then regardless. The OEM ecu is extremely underrated. It does a very good job learning once at operating temp as the o2 voltage can vary upon temperature. From my findings the USA and overseas ecu have the same self mapping abilities. Now that we have programs for complete control, it has opened up a lot. It does take a fair amount of tuning knowledge to get the most out of the ECU, however it is very capable.

4. The cold start solenoid’s sole purpose is to allow a controlled amount of air to help bring the bike up to temp a little faster. Once it sees a certain engine temp it shuts off. This helps speed up the time the learning system starts reading as well. It is not a “needed” sensor by any means. Without it on, the bike will warm up a little slower, may even act a little like a carb’d bike in a sense where it’s a little sluggish coming up to temp.

5. The CJR ecu we allow the option to keep or remove the self mapping system. We also offer to disable the tip sensor, cold start solenoid, decel fuel cut, and more.
While tuning, I will turn the learning curve off so the bike is in open loop. This means it is on a fixed fuel map, similar to a dirt bike. Once I am finished tuning, I will enable to learning system which helps target a good reliable AFR under the curve. After street testing we bring it back to the dyno for final verification everything looks good.

CJR vs DHM ECU - We both tune the ECU’s although we are different shops, we have different dyno time invested and create separate tunes for our builds. We are friendly and share information to help the community ensure that both flash options get great results. They are both reliable setups over stock and can only further improve your basic builds.

6. In a sense, the yumi and ecu flash do the same thing. Our reflash is modification specific vs 1 generic map. With both the CJR and Yumi reflash, you can technically achieve the same thing by changing injector and monitoring AFR to further fine tune the bike if on the same tune.
-For example, you have a bike with intake/exhaust and a camshaft. You have a custom tune at our shop from us that was 13.3 across the board. Now you add the PCX150 injector, this injector brings the OEM from 80cc/min to 130cc/min. With only an injector swap. The ecu will still target 14.7 afr under 80% throttle. However over 80% we will see the AFR go extremely rich as the injector is open the same amount of time that the ecu is tuned for, yet spraying 35-40% more fuel. You could add a certain size big bore kit and start playing with the intake/exhaust options in attempt to try and sort a proper AFR, however this is extremely time consuming and your end results still will not be extremely crisp.

The only full “self mapping” ecu I have seen is the finbro/cbr150 ecu. I am working on a CJR self mapping that will be similar, yet we will have control of things although it will be later this year if it works out.

I will post up some graphs of test I have done to explain a little further. In the mean time let me know if you have any other questions!


Sent from my iPhone using Tapatalk
 

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What is STFT and LTFT?

As for the ECU itself, I believe it's a Keihin ECU and according to the link below, it's a MSX ecu (vs Finbro that uses a cb150R ecu).


But yeah the throttle body thing makes sense for sure.

I guess the ultimate question for me is really:

Since I am not close to CJR or DHM, I'd get an "off the shelf" tune for intake/exhaust/cam. But is there a reason that these tunes are better than an ECU that can auto-tune?
I'm totally pleased with my Yuminashi self tuning ECU. I'm constantly experimenting with intake and exhaust mods and it always readjusts itself in about 50 miles. It's silly to have to constantly screw around with downloading programming, flashing, mapping, and adjusting trying to tune my Grom every time I make a change. It's been almost a year and I haven't touched the Yuminashi since the day I installed it.

It has ZERO cold starting issues. Yuminashi doesn't have the Finbro problem.The engine always starts cold with NO throttle input. And while it doesn't have a fast idle feature, the cold engine idles slow and rich but it doesn't die.
 

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I'm totally pleased with my Yuminashi self tuning ECU. I'm constantly experimenting with intake and exhaust mods and it always readjusts itself in about 50 miles. It's silly to have to constantly screw around with downloading programming, flashing, mapping, and adjusting trying to tune my Grom every time I make a change. It's been almost a year and I haven't touched the Yuminashi since the day I installed it.

It has ZERO cold starting issues. Yuminashi doesn't have the Finbro problem.The engine always starts cold with NO throttle input. And while it doesn't have a fast idle feature, the cold engine idles slow and rich but it doesn't die.
I don't recall cold start issues with the yumi setup. I did a lot with the finbro over the years and had generally pretty good luck. During warmup the finbro is in open loop until a certain engine oil temp, it shows sub 10:0 afr upon startup with no fast idle solenoid (cold harness button). Once the bike hits target engine temp and starts learning it did rather well to level out afr at idle as throughout the rpm range. I would bet if we can remap the finbro/cbr150 to pull a good 20-25% fuel off of the idle area the starting would be much better and the self mapping would continue to improve the rest of the areas. The self mapping setups have been nice for the average rider, I enjoy changing tunes and making the adjustments so the additional software is nice, however most people aren't into all that.
Tooter - Do you have the yuminashi for the OG or SF model? I have the OG one and SF one coming in soon, I've been told the sf is a bit different. I was unable to see any AFR changes during wide open throttle pulls while on the dyno but can revisit again this week as I am finishing up an OG build. Our original test was with a zoom loop, tb cam, and chimera intake. This was after a bit of around town/back road miles then put on the dyno. Partial throttle was okay over the learning miles, but wide open it didn't feel very good at all. With the graph below we could throw a PCX injector or maybe the F injector per recommended to fix the top end lean side of things however down low would be even richer WOT -
86066
 

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I don't recall cold start issues with the yumi setup. I did a lot with the finbro over the years and had generally pretty good luck. During warmup the finbro is in open loop until a certain engine oil temp, it shows sub 10:0 afr upon startup with no fast idle solenoid (cold harness button). Once the bike hits target engine temp and starts learning it did rather well to level out afr at idle as throughout the rpm range. I would bet if we can remap the finbro/cbr150 to pull a good 20-25% fuel off of the idle area the starting would be much better and the self mapping would continue to improve the rest of the areas. The self mapping setups have been nice for the average rider, I enjoy changing tunes and making the adjustments so the additional software is nice, however most people aren't into all that.
Tooter - Do you have the yuminashi for the OG or SF model? I have the OG one and SF one coming in soon, I've been told the sf is a bit different. I was unable to see any AFR changes during wide open throttle pulls while on the dyno but can revisit again this week as I am finishing up an OG build. Our original test was with a zoom loop, tb cam, and chimera intake. This was after a bit of around town/back road miles then put on the dyno. Partial throttle was okay over the learning miles, but wide open it didn't feel very good at all. With the graph below we could throw a PCX injector or maybe the F injector per recommended to fix the top end lean side of things however down low would be even richer WOT -
View attachment 86066
I have the OG and moved 4 wires. I asked Yuminashi repeatedly online if their new SF has any different operating parameters from the OG, and they wouldn't answer. Did Yuminashi tell you the SF is different?

As an experiment I tried both the 140cc/min and 120cc/min injectors just to see how much the ECU could compensate by shortening the duty cycle. The 140 was too much, but the 120 had superb throttle response in the lower rpm range. Gas mileage took a hit so I went back to the stock 90cc/min injector as I'm just a regular transportation rider..
 

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Discussion Starter #13
cu. I am working on a CJR self mapping that will be similar, yet we will have control of things although it will be later this year if it work
Awesome! Appreciate the information. Sounds like this eliminate the Yuminashi ECU for contention for me. If the CJR ecu tune also has the same self tuning capabilities but have parameters a bit more optimized, I think this is the best of both worlds.

Looking forward to the new CJR self mapping!
 

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Awesome! Appreciate the information. Sounds like this eliminate the Yuminashi ECU for contention for me. If the CJR ecu tune also has the same self tuning capabilities but have parameters a bit more optimized, I think this is the best of both worlds.

Looking forward to the new CJR self mapping!
Self tuning ECU's are the wave of the future. I love my Yuminashi because I don't have to waste time screwing around with it every time I make a change. :)
 

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Discussion Starter #15
Self tuning ECU's are the wave of the future. I love my Yuminashi because I don't have to waste time screwing around with it every time I make a change. :)
It is really nice. I had gotten my Grom so that I'd stop tinkering with the car. A lot cheaper messing with the Grom than the car. lol.
 
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