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Finbro ECU and Cold Starting

This is a discussion on Finbro ECU and Cold Starting within the Grom Talk forums, part of the Honda Grom Forums category; I ran the 183 for a while, until the Man told me I couldn't modify the capacity on my bike without updating the papers, and ...

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    Finbro ECU and Cold Starting

    I ran the 183 for a while, until the Man told me I couldn't modify the capacity on my bike without updating the papers, and I couldn't update the papers without homologation (type approval, something like DOT-approval) papers- which obviously don't exist. So now I am back to 125cc.

    While I had it, I was using the finbro ECU together with Moriwaki megaphone exhaust and stock airbox just with the usual internal airbox pipe modification.

    Anyway... the problem I had was getting the damned thing to start. Here's a video of how that went:


    I found that once the bike was started and warm, I could adjust the idle screw and have it idle really smooth about 1,500rpm. Some said this is too low, but for me it was absolutely fine and any higher meant it would 'lean hang' at 3,000rpm on the way back down to idle.


    Once warm it would start much better, but still not really great.


    From a few Facebook page threads I have the feeling I am not the only one who had that same issue. So here's what I suggest as a solution - however please note this is untested and you try it at your own risk.

    Here's a wiring diagram for the Grom. You can see down in the bottom right there's the 'fast idle solenoid valve'. We know the Thailand models don't have this, and we know the Finbro ECU doesn't have an output for it. It's my belief that this is why the bike wouldn't start. It'd be nice to have a decomp on the camshaft too, but I don't think it was the main problem.



    The cold start valve is just a simple solenoid as opposed to the stepper motor type on some more advanced EFi systems. It takes a live feed from the EFi fuse (Black/White) and has a switched earth (Yellow/Orange). My guess is the stock ECU switches to earth depending on what the EOT (Engine Oil Temperature) sensor is reading. But we know the Finbro ECU doesn't have this feature.

    So why not manually give the solenoid an earth when you want it to operate? Before I had to revert to 125cc I was going to get a simple handlebar switch, and wire it in between the Y/O wire and earth. Switch it on to activate the solenoid, or off to deactivate. If I am right, this should give you a manual cold start option.



    You can also buy thermo switches in the right kind of range. I wondered if it might be possible to put a low range (say 45 celsius) switch between the solenoid and earth, to have a kind of auto choke?
    KSD 9700 Temperature Switch Thermostat Normally Closed (NC) Thermal Protector | eBay

    I'm not sure if there is a way to use the existing EOT for this, or if that might interrupt something else the ECU might be using that signal for.

    Be interested to see what you guys do with this information/idea. It's something that's really essential unless you live in the desert, and it's just plain missing on the Finbro ECU. This could be a super simple fix for like $5 and a little of your time. I can see this being something for Cisco and his ongoing R&D projects - but this could be a lifesaver for anyone for whom that first video has become normal life.

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    Wow I'm guessing the Man must be relatively knowledgeable in your area. I had my cbr250 Grom inspected by the man as part of my titling process, he thought it was a 125 and I wasn't saying any different. It passed.
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    The no cold start feature SUCKS. Might as well have a 40yr old carbed bike.

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    Quote Originally Posted by Fox85 View Post
    Wow I'm guessing the Man must be relatively knowledgeable in your area. I had my cbr250 Grom inspected by the man as part of my titling process, he thought it was a 125 and I wasn't saying any different. It passed.
    There was a fuck up at the customs desk when I was importing the parts - I went to collect them on my MSX. The customs man spoke to the police colleague and my number was noted. I live in a REALLY small place.

    Quote Originally Posted by GlockPointer View Post
    The no cold start feature SUCKS. Might as well have a 40yr old carbed bike.
    So here it is - give it back to yourself with this mod.

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    Quote Originally Posted by a_morti View Post
    You can also buy thermo switches in the right kind of range. I wondered if it might be possible to put a low range (say 45 celsius) switch between the solenoid and earth, to have a kind of auto choke?
    KSD 9700 Temperature Switch Thermostat Normally Closed (NC) Thermal Protector | eBay

    I'm not sure if there is a way to use the existing EOT for this, or if that might interrupt something else the ECU might be using that signal for.
    If you were to go the the thermo-switch route, youd need a way to get it into/get the heat from the engine decently, rather than just taping it to the cylinder or head.

    If you wanted, you could tap off the EOT sensor, using a wheatstone bridge (or this: https://en.wikipedia.org/wiki/Resist..._configuration), coupled with some sort of switch dependent on the voltage out of the wheatstone bridge. This switch would most likely have some zener diodes in it and some other stuff... hmmm... Ill look around, draw some diagrams, yaknow.

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    I could never get the A/F mixture to settle down to 13.2-13.9 range when cruzing or just nomal riding with the Finbro ECM and cold start was worst like you said and I was using the USA wire harness with the a couple of wire moved around and one disconnected and I was getting indication of very lean A/F reading about 16-18 while riding and when going to WOT the grom would sort of hesitated then speed up then lose power so I removed the Finbro ECM and went back to the PCV-WB02 unit. I guess I would have continued testing with the Finbro ECM but I had other projects in the way such as restoring my 1982 RX7 and getting the car smog and I just wanted to enjoy riding both my Finbro 183 and the BrianS 170 groms.

    Looking at the idle circuit unit that goes on the throttle body, it looks like the spring and plunger unit that is mounted on the side of the throttle body blocks a hole that lets in a little more air than normal and looks like when you turn on your key to start your grom the circuit will pull the plunger away from the hole to unblock it and let more air into the throttle body for start up.
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    I don't have an AF gauge but seat of the pants dyno says the bike ran great on the finbro ECU - when it was warm. It did take a good 5 mile ride to settle itself down though.
    I was using the 6 hole injector from Finbro and the big fuel line.

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    Hmm haven't installed mine yet, and my bike will be mostly a summer bike here in Tx

    Hopefully won't be a prob

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    Last edited by RACER X; 03-03-2016 at 09:02 AM.
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    its my plan to pop a lil switch on the bike to activate the solenoid when i get my finbro ecu. Shouldnt be hard as like the OP stated the ecu simply grounds out the line opening up the lil port.

    Its pretty common on fuel injected dirbikes to essentially have the same thing but manual. My WR450F has a lil plunger on the throttle body that you pull out when its cold.

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    I don't find it that hard really. On my bike once I made sure the high idle valve was disconnected and the iat sensor disconnected. I have mine idle right around 1500 rpm (warm) with the throttle plate full close and air screw used to adjust idle. When it's cold I crank it till it fires and let it idle with the throttle cracked open just barely. It sputters and pops till she is warmed up then the bikey runs fine. Only takes a couple mins at most. Once warm she fires right up.


    If you guys do run the solenoid with a switch might want to make sure it's 12v going to it. A lot of sensors only run on 5v not sure if the solenoid does or not.
    Last edited by badassxr50r; 03-03-2016 at 11:21 AM.
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