2010 GV250 EFI missfire

Hey welcome!

Have you tried these ?

• Go to airbox or the frame look for a device that has wires going to it in one side  , then other side has 2 pipes sending air around the motor and throttle bodies
  That’s your IDLE SPEED CONTROL VALVE
  If its haywire ,  it could be the reason.
• Ignition coils = Did you swap around ?
• HT leads = Did you swap them around ?

I have a suspicion it’s something to do with wires near the rear cylinder  (connector plug corrosion on rear cylinder ? or the coil ? or HT Cap itself (use NGK) ,

Sounds silly, but please slowly remove the ECU from the harness and carefully use “AIR DUSTER” only  and blow out any debris that might enter in to it.

Also use a “SMALL AMOUNT” of   – CONTACT CLEANER – on the ECU pins and it’s giant plug – It is a very very difficult part to buy as Korea stopped making them.

Wait overnight to fully dry out, as you don’t want to start the bike and fry the ecu if its pins are still wet.

This might improve signals going to the sensors in the bike to make it run properly.

what waiting for the ECU to dry out,    clean the rest of your harness connectors involved and possibly the sensors if there is a suspicious of debris invasion in them or rust / oxidization of pins.

Trevor wrote:

I just bought a 2010 GV250 EFI and the rear cylinder has a misfire. I have replaced both sparkplugs and verified they have spark and I have even swapped the injectors. No matter what I do the misfire stays on the rear cylinder. Idle rpm is also at 5000 while warming up and even tho the throttle body is closed. I don’t know how to fix it.

Quote

Unplug your O2 Sensors first front see how it behaves then plug it back in and unplug  the rear one see how behaves. If it improves with 1 unpluged you know ones bad if you unplug both and it runs fine gotta further diagnose. there’s also a small black Idle speed control valve on the bottom right of the tank by the fuel hose. Your airbox will have the airhose that feeds that vacumm circuit you can plug that and see if your butterflies are truely “closed” or not.