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Hello All. New Member here. PLEASE HELP!! I have searched everywhere for a solution to my problem, hopefully someone out there will be able to help. Here is my issue. The ATV in question is a 2009 Honda TRX420 FPM, FUEL INJECTED with power steering, ONLY 3300 km. The bike starts easily every time, and idles like a champ. It even revs up to about 2000 to 2500 RPM (just guessing) perfectly, HOWEVER, when I try to rev it up any higher, it starts to act like it is being starved for fuel - sputters and runs rough. If I keep giving more gas, it will slowly develop slightly higher RPMs but still sputters. If I back off the throttle quickly, it will often backfire. I have a video for anyone that needs it. PLEASE NOTE, this is FUEL INJECTED and NO ERROR CODES are being displayed on the dash. ALSO, this is a new ATV to me so I do not know the history. I didn't notice any of these symptoms when I purchase the ATV (I have owned many in my 56 years, so I kinda know what to look for). I did, however, PRESSURE WASH the quad when I got it home. Not sure if this is what caused my issue. Here is my TROUBLESHOOTING THUS FAR: 1/ Replaced fuel filter, 2/ Checked valve lash (perfect), 3/ Replaced spark plug 4/ Drained fuel tank, removed petcock and inspected filter screen (it was clean), filled with fresh gas, 5/ Checked fuel pressure (it was 50 psi at idle, similar when attempting to rev). Checked voltage to pump (was 13.8 volts) 6/ Checked voltage at battery (14.2 volts when running), 7/ Inspected PGM FI unit connections. There was a lot of mud around the unit and other relays etc, and I saw evidence of muddy residue inside connections. Cleaned the PGM FI connections, as well as the other connections, with electrical contact cleaner. 8/ Removed muffler (no change) 9/ Replaced injector with new OEM part, 10/ Replaced coil with new aftermarket coil, 11/ Replaced TP/Map sensor with used part, 12/ Cleaned all connections from engine back and re connected using dielectric grease, 13/ Cleaned main ground to frame, 14/ Removed and cleaned throttle body, 15/ Removed and inspected IACV (moved freely), 16/ Replaced PGM FI unit with used part. PLEASE NOTE: Engine seems to rev properly when petcock is closed and just before it runs out of fuel. If petcock is just cracked open just a hair (restricting fuel flow to pump), bike will rev well until it runs out of fuel. To me it appears it is getting too much fuel, which is supported by the fact the plug is black after running for a while attempting to rev. I HAVE NOW RUN OUT OF OPTIONS, AND MONEY FOR PARTS THAT DON'T WORK!! Any help would be greatly appreciated, and thank you all in advance. Will
 

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Did you put an NGK spark plug in it? Champions don't work in most motors. Check the spark plug cap and boot, if there is a resistor in there it could be burnt. I would put all of the OEM Honda parts back on it (ignition coil etc.) that were swapped for china too. The TP/MAP must be reset as well, now that its been disturbed. See the attachment. Make sure the sensor in the airbox is plugged in.... Does the MIL light work? Can you hear the IACV stepper motor run for a second when you turn the key on?
 

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Hi there. Thanks for the reply. It is an NGK plug and has been gapped as per specs. The cap and boot look fine, no cracks or anything visible. I did reset the TP/MAP sensor as per the service manual (I have a copy). The MIL light does appear to function correctly, and the air sensor is plugged in. I do hear all three sounds when the key is turned on - the fuel pump, the IACV and the fuel relay at the back. To me it seems as though it is getting too much fuel when I try to rev it (it will rev properly if the petcock is closed and just before it runs out of fuel, or if petcock is just opened a hair restricting fuel flow). The thing is, NOTHING changed even after swapping out parts one at a time, which leads me to believe these parts were not the issue. Just about ready to give up and sell it.
 

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It sounds like the PCM is receiving severe cold weather startup data doesn't it...? In other words the PGM-FI system might be enriching the fuel mixture like you'd do on a carbed motor by choking it... in sub-zero temps. I'd check the ECT sensor condition (someone may have overheated the motor once, killing it) and its wiring/plugs all the way to the PCM. Let us know how it goes if you can.

EDIT: Test the sensor in the airbox too if you can.
 

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Hi: Did you change the fuel filter in the sub fuel tank -- that will give you that problem you are getting
 

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Thanks for all of the replies everyone. I gave up on the quad and sold it yesterday!
Haha, that's one solution to the problem!!

I was going to ask if you'd replaced the fuel filter on the pump, replaced the fuel line and what colour the spark plug was. It's irrelevant now but I'm still curious.
 

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Discussion Starter #8
Just thought I would post one more time on the problem. As I said, I sold the ATV, fully disclosing the issue, and all troubleshooting steps taken, to the new owner. I asked that he let me know what the solution was when he finally found out. He took the ATV to a Honda dealer, who was also stumped by the problem. The dealer ended up contacting Honda itself for a solution. According to the new owner, the issue is that the timing chain jumped a tooth!! Not sure how that happens, but after seeing many posts on this issue affecting 420s, I suggest that maybe this is a problem for the 420s. Anyway, I hope that this can help someone some day that is faced with the same issue.
 

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Thanks for the update
Do you think you would have caught it if we thot to check the valve settings?
I’ll keep that in mind if i hear another instance
 

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If it 'skipped time' then the maintenance schedule clearly wasn't followed.. It's stated for a reason.
We can only assume these procedures are followed when answering fault diagnosis questions.

As said in 90% of threads answered to, have you checked the timing?! Lol.

One person I'm sure would have mentioned timing would be @shadetree
 
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