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Discussion Starter · #1 ·
Hey everybody, this is my first post! I've found some useful information on this forum, but nothing that it quite like my situation. I recently picked up a 2009 420 AT power steering to fix and sell for a profit. The guy said he just had the whole motor rebuilt from top to bottom, he has swapped the throttle body from a running fourwheeler, and tried a new PCM but nothing will straighten it up. While I have had it, I have put new good fuel in it, changed the oil and filter, installed an entire new fuel pump, and put an hmf on it it because I bought it with no muffler. I could
Not hear it turn over when I bought it, but I new it was not running correctly. It seems like it it still doing what it was with the previous owner from what he has told me though. It will turn over, but will not start until about half throttle, and when it does start, if the throttle is pushed all the way it runs rough and sounds like it's running about one-quarter to half throttle. I can let off the throttle to about one-quarter throttle and at this point it sounds like it could be idling. And when I let off completely it will cut off. I have tried to look up codes in the service manual but I cannot find one for 4 short blinks which is what is shown. Also, the is a plug that is broken off in the front of the motor on what an OEM parts section called the "main valve body" but I'm not sure what it actually is or does. Any help would be greatly appreciated if anybody has any advice to give. Thanks in advance!
 

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Discussion Starter · #2 ·
So I figured out where the plug was broken off, and that's from the A/T solenoid valve which by looking in the manual I believe is why it is blinking 4 times, so that is out of the way now. At least until I can get it running and make sure!


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Welcome to the forums! I'm no good help with EFI so hopefully someone will come by in a bit to talk about yours. Have fun!
 

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try re-setting the TPS sensor ( throttle position sensor ), the service manual should show/tell you how.
 

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Discussion Starter · #5 ·
Shadetree, I will try that whenever I get a chance to mess around with it again and let you know the outcome.


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Shadetree, I will try that whenever I get a chance to mess around with it again and let you know the outcome.


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good deal, please keep us posted ! :).
 

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Discussion Starter · #7 ·
so i got a chance to try the reset procedure, but I'm not sure if it worked or not. I tried it 2 times following the directions in the service manual and it never seemed to change or give the outcome described in the manual. I am almost sure i did it right though. So i may try it again and see if i can get it right. But also, i was able to reset the codes it was throwing with the A/T soleniod valve and it never threw anymore codes after that except for just repeating that same 4 short blinks. I have a buddy with a 420 2wd that is going to let me check my IACV with his good one. Also, I'm debating on going ahead and replacing the TPS just to be safe so that i know its good. Any thoughts?
 

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Discussion Starter · #8 ·
i tried again this morning to reset the tps. I had more luck getting the reset pattern blinking on the MIL like the manual says, but I'm not sure if it is complete or not. i have included a screenshot of the manual, so can one of yall tell me how i know it is complete? in the instructions it says that when the pattern changes to the confirmation pattern that the reset is complete, but underneath the diagram of the pattern, it says that if the reset confirmation is still blinking that the reset is not complete. I have tried it 3 times, the first 2 times this morning i turned the key off when the confirmation pattern showed, but it made no difference in how it started. The third time, i have left the confirmation pattern blinking and after about 30 minutes at least of blinking it has not gone off. So I'm guessing it has reset, but the outcome has been no different.
 

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I truly wish I could be more help to you ?, but, those models are just out of my know-how !..lol. this is why I stick with a manual shift, no bells, whistles, or anything else that makes my day harder ?!..lol. even though both my 2003 trx450fm, and my 2005 trx500fm have some switches on them to engage the front differentials ?, only other thing they have are speed sensors to tell my dash how fast i'm going while sipping my '' cold one ''..lol.
 

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Discussion Starter · #10 ·
If it wasn't such a good deal then I wouldn't get an A/T because like you I could care less about all the bells and whistles! Too many sensors and electrical stuff that only drive mechanics nuts trying to fix them! I think I am going to try to replace the tps and IACV next and see where that takes me. Thanks for your input!


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If it wasn't such a good deal then I wouldn't get an A/T because like you I could care less about all the bells and whistles! Too many sensors and electrical stuff that only drive mechanics nuts trying to fix them! I think I am going to try to replace the tps and IACV next and see where that takes me. Thanks for your input!


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your welcome, yes..please keep us posted on your progress :).
 

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Melatv has been a huge help with me working on the 420's.

The IACV controls idle speed on the EFI models. Take out the two tamper proof bolts on top and pull it out and ensure that it spins freely. Turn the key on while holding the IACV and see if it spins in and out freely (which it does upon turning the key on, when the system initializes)

On the valve assembly, I broke on of mine off, but was able to epoxy it back in place and was shocked that it still worked. It is simply an "on/off" style solenoid, so if you can get it back in place with the contacts making a good connection you might be able to salvage it. If not, you'll need a new valve assembly, and they are $$$.

Code 4 looks like the error from the valve not having a good connection. I would fix that first and see what you get.

You can also remove the injector from the throttle body and ensure that you get a good spray of fuel when you turn the key on. You should get a good spurt when you first turn the key on.

When you turn the key on the EFI models you should get a buzz/ rattle noise (IACV), and you should see several dash lights light up for a few seconds as the system initializes.
 

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Discussion Starter · #13 ·
Melatv has been a huge help with me working on the 420's.



The IACV controls idle speed on the EFI models. Take out the two tamper proof bolts on top and pull it out and ensure that it spins freely. Turn the key on while holding the IACV and see if it spins in and out freely (which it does upon turning the key on, when the system initializes)



On the valve assembly, I broke on of mine off, but was able to epoxy it back in place and was shocked that it still worked. It is simply an "on/off" style solenoid, so if you can get it back in place with the contacts making a good connection you might be able to salvage it. If not, you'll need a new valve assembly, and they are $$$.



Code 4 looks like the error from the valve not having a good connection. I would fix that first and see what you get.



You can also remove the injector from the throttle body and ensure that you get a good spray of fuel when you turn the key on. You should get a good spurt when you first turn the key on.



When you turn the key on the EFI models you should get a buzz/ rattle noise (IACV), and you should see several dash lights light up for a few seconds as the system initializes.


I have taken the IACV out and made sure that it was moving freely and that the rod on it was not bent. It does come on and spin perfectly when the key is turned on. And the new fuel pump buzzes as well as the IACV when the key is turned on as well.

Also, I was wondering if some kind of epoxy or something similar would work, so I will have to try it now that and see what it does. The new valve assembly is $170 just for the front piece with the plug on it, so any way to save it will be good with me!

I will pull the injector out and see how good of a spray it has, and also i am going to try and find a buddy with a TPS I can steal for a little while and possibly an IACV. But I am wondering it could be something with the reset procedure on the TPS because the pervious owner said he swapped throttle body's and I have also had the tps unplugged too. Too many things it could be on these new electrical fourwheelers! Thank you so much for the help tho.
 

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Discussion Starter · #15 ·
"Check engine light" is on but I haven't counted blinks if it's even blinking. I just know that it is on but I am going to look into it throwing codes through the "check engine light". And yes I do have an FSM pulled up on my computer at home that I have been looking through to help me. I will check the lights and check back in and let everybody know!


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I'm not familiar with the electronics on your machine, so disregard my comments if they aren't relevant...?

I have worked on many of the early (simplest, aka "dumbest" systems) mid (a bit "smarter" with self monitoring) and late (complex with error reporting/logging and several degrees of adaptation to failures built in) control systems on cars, snowmobiles, motorcycles etc, over the years as those systems evolved. By the late 1990s many of those simple systems began to appear with an "initialization failure mode" (nowadays commonly called "limp home mode"). This is a catastrophic failure within the monitoring/control electronics where a critical component stops responding to signals, is disconnected (open circuit) or is stuck/broken/non-functional. Some of those simplest and cheapest control systems (on sleds and bikes) in the late 1990s/early 2000s would fail to initialize when the key was turned on if a major component had failed...

That failure to complete the initialization process left the system(s) completely inoperable. Any attempt to start and run the motor sometimes meant that it would barely run at all. I remember a 2-stroke sled I worked on that had exhaust port power valves and EFI that would barely run if I could even get it started... After many hours of diagnosis and a bunch of head scratching, I realized that all the necessary controls (fuel injectors, TPS, Ignition advance, power valves etc.) were being disabled by the ECU as soon as the key was turned on!

I finally traced that problem down to a failing worn out power valve... it still worked perfectly while I was testing it, so it took me quite a while to figure out what was going on! I eventually measured the current draw through it and found that the small electric stepper motor inside of that valve was drawing too much current through the ECU! So when the ECU went through its initialization and self-test when the key was turned on, it actuated that valve normally enough to fool me, but then shut itself down leaving everything else in the system inoperable. I swapped that power valve for a new one... and like a good magic trick, everything worked perfectly and the sled ran great! Big lesson learned....

This was one of the cheapest EFI systems on the planet at that time... so it surprised the crap out of me how easily I was fooled by its behavior. They have since become much more sophisticated.

So the point I'm trying to make here with this long rant is...? Its possible that a single failed component within the monitoring/control loop has failed in some manner... such that none of it is working and won't ever... until that single fault is found and fixed.

Hope its a cheap and easy one!
 

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The 420's can be a bit of a PITA to troubleshoot. Mine had all sorts of issues getting it to run which could all be traced back to the fuel injection relay not making a good connection. That, however, kept the initialization from occurring when I turned the key on.

You can bypass a lot of the components on the 420's by running a wire from the battery + directly to the red black wire on the coil. You could try that and see if it does anything differently, but when I have had problems with the 420's I found that just about any component that was iffy would result in a no-spark at all situation, which is obviously not what you describe.
 

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Discussion Starter · #18 ·
Retro, when you describe the limp mode on the sled, was it like it would idle and crank up fine, but once given throttle it would not take it or have any power? I've had a couple of buddies with Chevrolet trucks that went into limp mode due to lose grounds on the battery and failed ECU's and this is what they described. It would crank up and run fine but did not have any kind of power at all, and maybe would go 5 MPH. If you could, please elaborate on the symptoms of this "limp mode"

Jeepwm, it has fire and what looks like a strong spark. I have checked it multiple times and it is good. I checked valve clearance and it seemed to be okay also. And the motor has 120 lbs of compression. So it leads me to believe it's a fuel problem which on the EFI's could become a electrical problem. A bunch of head scratching and trial and error I guess!


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So you have a good oem fuel pump with clear filter, right? Do you have good flow from the petcock to the fuel pump? They can become partially clogged in either place and cause problems.

If both of those are definitely good and clear, I would pull the injector off and turn the key off, see if it sprays. You should get a good, strong spray when you initially turn the key on.
 

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Discussion Starter · #20 ·
So you have a good oem fuel pump with clear filter, right? Do you have good flow from the petcock to the fuel pump? They can become partially clogged in either place and cause problems.



If both of those are definitely good and clear, I would pull the injector off and turn the key off, see if it sprays. You should get a good, strong spray when you initially turn the key on.


Yes, OEM fuel pump. Came with a new filter in it. I do need to clean the petcock out because the reserve position on it doesn't seem to have good flow, but the ON position does. When I installed the new fuel pump I put the rubber washer thing and the new clip on the fuel line going from the pump to the throttle body. I put new ones on the fuel pump side and the throttle body side and while we had the line loose we turned it over to let it pump fuel through the line to see if we could get the old gas out and we had a good steady stream coming through the line. But I will check the injector as well and make sure that it is spraying good


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