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Finbro cold starting fix!

This is a discussion on Finbro cold starting fix! within the Grom How-To's and Guides forums, part of the Honda Grom Forums category; Figured I would seperate this out from the long thread found here -> https://www.hondagrom.net/forums/7-grom-talk/10270-finbro-ecu-cold-starting.html I am 95% positive i have found a solution!!!! Background / ...

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    Finbro cold starting fix!

    Figured I would seperate this out from the long thread found here -> https://www.hondagrom.net/forums/7-grom-talk/10270-finbro-ecu-cold-starting.html

    I am 95% positive i have found a solution!!!!

    Background / What we know:

    The stock ECU actually does enrich the mixture to make cold starting much easier when paired with the high idle valve. This was very easily seen via a volt meter across the injector. Stock ecu, cold motor, start the bike, watch the voltage at the injector (pcx 150 injector in my case), listen for the lil POP of the high idle turning off and you instantly saw a ~20-25% drop in voltage of the injector. In other words, with the stock ecu any time the high idle valve is opened by the ecu, it also feeds the bike ~20% extra fuel. Exactly what you need for a cold start.

    The problem we have with the finbro ecu is the fact it doesnt 1. use the high idle solenoid by default (that allows extra air in at idle), but mainly 2. It does NOT add extra fuel to the mixture when the motor is cold for cold start enrichment.

    We also know, the check engine light, high idle valve, and more importantly the injector are all GROUND SWITCHED. That is important.


    So i went back to my original design here:

    https://www.hondagrom.net/forums/7-gr...tml#post138248

    And tweaked it a little, I added in a very simple circuit to hold the injector open a little longer thus increasing fuel at idle to the motor (SAY WHAAAAAT?!?!)

    I used my original design (which turn on the CEL and High idle valve together). Changed my switch to a DPDT (which is really just used as a DPST) switch, so i had another isolated circuit to play with that was switched at the same time as the CEL and high idle valve. This extra switch circuit was used to ground out the negative side a 68µF 25V electrolytic capacitor, where the positive side was tapped into the injector wire (pink / green, pin 16 of the ecu). The 68µF Cap gets discharged relativly VERY quickly when the ECU grounds out the injector for one of its pulse, but then when the ECU stops grounding out the injector, the injector can STAY OPEN longer as current can still flow through it to charge up the Cap. 68µF seemed to be ideal after some trial with various other sizes. It supplied right around a simulated extra 20-25% duty cycle at idle for my setup. Thus properly supplying the motor with the much greater amount of fuel needed for an easy cold startup.


    Note YOU DO NOT cut the injector wire, you are simply tapping into it. (Obviously it goes without saying, you do the above, any damage is on you)




    Here you go gents,

    Seems to of definitely helped cold starting!!!


    Last edited by nd4spdbh; 03-22-2016 at 10:20 AM.

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    That's pretty cool. How does it run otherwise? I may have to switch to the Finbro ECU.

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    Quote Originally Posted by TheBallew View Post
    That's pretty cool. How does it run otherwise? I may have to switch to the Finbro ECU.
    Mine runs like a champ. It just requires you run the right injector for your set up.
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    Mine runs great with the finbro ecu. Pulls real good. Set it n forget it style, i like!
    321GromInk likes this.

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    Gotta say, came home today, le grom had not been ridden in over a day. Hopped on her, flipped on the cold start switch, turned ignition on, tumbed the starter switch really quick and she sprang to life.

    Instantly started riding, left the cold start on for about 2 min while she warmed up, then flipped it off and all was still good.


    SO MUCH happier with this experience with the finbro ecu, I was so used to stock where you could get on it from dead cold and just go, and my cold start switch has brought that back.


    I will be interested to see what its like in cooler temps as its been pretty mild around so cal this past week. (That video was shot when it was 60*F out)

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    I'll have to get it put on mine and try it. It's been down in the low 50's here. 40's at night.
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    So, who's going to be the one to assemble and sell a kit? I imagine there's a lot of people who would want this to retrofit. Perhaps Franco could offer it with the ECU? Or HR as a drop down option?
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    This solves a huge problem. I replaced the starter (wemoto) & the battery (shorai) and the cold start improved slightly meaning I didn't kill my battery starting it. It would still take 3-4 min. 1 min to put load on the battery, 1-2 min of cranking. Was a joke.
    Thanks for this info. Does the 31 mm TB finbro sells support the high idol valve?

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    Just bought a ECU so Subed.... for later use
    321GromInk likes this.

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