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Old 07-25-2011, 06:14 PM   #1
350z1485
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C28 Error Code

Hi Guys,

This is going to be a long discussion so bare with me. A couple of weeks ago I rode into work and everything was running perfect. I have a K5 gsxr 600 by the way. During lunch, I noticed my bike started bogging down at around 7000 RPMs. No error code at the time though. Come to find out I had an aftermarket headlight wiring harness after reading through a bunch of forums and I replaced that with an OEM headlight wiring harness. After replacing the harness I got an FI code and then preceded to put it into the dealer mode to find out I had a C28 code which is the STVA. Long story short, I took the STVA out to inspect the soldering connections and sure enough one connection was broken but very hard to see and on top of it all, it tested fine electrically. Anyways, i put everything back together and took it out for a ride. Well no more code and it accelerates fine now. However, my bike all of a sudden seems to be running extremely rich. Never had any problems with revving the bike. Now when I rev the bike it shoots out a 6" flame out the back and then almost stalls. At the low RPMs (~3K-5K) the bike will accelerate and cut out without even moving the throttle. I have full exhaust and no power commander however keep in mind the bike did not run like that at the lower RPMs before I had the issue with the STVA. Any suggestions?
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Old 07-25-2011, 06:58 PM   #2
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Re: C28 Error Code

Pretty common for them to test good on the bench, but still throw a code unless they're properly repaired. Sounds like you messed up the reinstallation. The STPS is spring loaded and it's pretty easy to get it put back together in the wrong position.

Try this:

1) remove the STVA.
2) Use a small flat screwdriver. Insert it only enough to turn the STVA and turn it fully clockwise.
3) Turn the secondary plates to the fully closed position and reinstall.

Also, check to make sure you haven't reversed the plugs from the TPS and STPS. The STVA plug is pretty obvious. The TPS plug is gray. The STPS is black.
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Old 07-25-2011, 07:12 PM   #3
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Re: C28 Error Code

Alright. Well I am not getting any code anymore but its possible I put it back wrong. If its not in the right position though wouldn't I get some code. I can open the valves all the way and close them. But I will certainly try that anyways. I think the STVA is working properly because I took it out for quite awhile and no issues where as before it would give me a code immediately after wot.
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Old 07-25-2011, 07:22 PM   #4
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Re: C28 Error Code

Let me know what you find. The headlight harness shouldn't have caused any FI problems, so it might just be coincidence. They shouldn't cycle fully if the STPS is in the wrong position, unless it's damaged.

How long have you had this bike? Do the secondaries go though the startup routine fine? Start with them closed. Turn the key on. They should cycle to full open and bump slightly back towards closed. Then start. After about 4 seconds, they'll close.

If it's spitting fire, it could be really rich, and it could have the PAIR system blocked.
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Old 07-25-2011, 07:46 PM   #5
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Re: C28 Error Code

Yea the headlight wiring harness didn't cause any issues it just prevented me from putting it into dealer mode to get the code. My gage cluster always said chec instead of the engine temp and sure enough after reading through enough forums people said that was the result of an aftermarket wiring harness. But anyways the valves go through the proper startup and go wide open and then close slightly and then after startup they close fully and open slightly as you give the bike more throttle. The issue that troubles me is i fixed the stva issue that I was getting and not my bike seems to be running really rich and rough at low rpms which wasn't happening before all this.
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Old 07-25-2011, 07:53 PM   #6
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Re: C28 Error Code

Does it have a powercommander? Might have been tuned to run without the STVA. Hard to tell with a used bike. Could be anything, including physical cam timing.

CHECK EVERYTHING!
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Old 07-25-2011, 08:25 PM   #7
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Re: C28 Error Code

No powercommander but thinking about getting one. Not sure if that would solve my problems or not. I can not think of anything else that would. I have been struggling with this for two weeks and thats basically my last resort. But what doesn't make sense is I never had these issues before all this.
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Old 07-25-2011, 08:59 PM   #8
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Re: C28 Error Code

Could be the IAP, or IAT sensors giving a bad value too. It's really hard to tell where to start without seeing the bike in person.
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Old 07-26-2011, 07:57 PM   #9
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Re: C28 Error Code

If you are available tonight I could swing by? lol. I messed around with the TPS today and adjusted it based on the voltage. I heard some people had success with it set at 1.2 V and other people said it ran good at 1.3 V. Good news is it doesn't have the jerky throttle that I was experiencing after fixing the STVA. I am still running rich but with the full exhaust it was probably always running rich. I think I might have a couple more of adjustments to do because it still seems to stall if the RPMs drop to quickly (i.e. shifting down gears when decelerating or coming to a stop). I still have to adjust the idle slightly. Running at about 1500 RPMs now so its close but needs to be lowered about 200 RPMs still. Anyways, I think I am on the right track because the bike is running well now through all of the RPMs minus the fact that it stalls if the RPMs drop too fast. When I figure it out completely Ill post what the issue was. Thanks for your help TheGeek
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Old 07-30-2011, 10:09 PM   #10
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Re: C28 Error Code

So I think I have figured everything out..Well I hope anyways. The bike seems to be running much better. Still a little rich at lower RPM's but with the full exhaust I think it was always running slightly rich with stock tuning. Anyways, I adjusted the STPS sensor as well as the TPS sensor. The voltage that I adjusted the TPS sensor to was 1.3 V. With both adjustments the bike is not stalling and is smooth while riding at low RPM's. We will see how rich I am actually running based on my MPG. I appreciate all the help!
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Old 07-31-2011, 05:50 PM   #11
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Re: C28 Error Code

I am looking at a friends bike for him and he is receiving C28 and C29 on his 04 600. When the bike is started the butterflies are not going through it's normal cycle. I pulled the Valve off the bike and the lil motor is not moving. Any help would be greatly appreciated.
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Old 07-31-2011, 08:25 PM   #12
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Re: C28 Error Code

If you put the STVA back on incorrectly and forced it to close, you've probably damaged the STPS.

Did you get only C28 before and then both C28 and C29 after you attempted to reinstall?
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Old 08-01-2011, 08:15 PM   #13
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The bike was brought to me throwing both codes. He said it ran fine and then when he went to go ride again it wouldn't start.
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Old 08-02-2011, 06:38 AM   #14
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Re: C28 Error Code

99% of the time, both codes show up because of user error.

Either they've decided to remove and reinstall the STVA and screwed that up, or they've mixed up the plugs for the TPS and STPS. Or, they damaged the wires trying to do something else.

The fact the the bike was running and isn't now kinda points to the sensors being reversed. But that's just a wild guess.

The 04/05 STVAs are prone to failure. But they rarely have mechanical problems. If the secondaries were hard to move, chances are your buddy fucked something up and isn't owning up to it.
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Old 08-02-2011, 07:53 PM   #15
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Awesome. Thanks for the response. I am going to double check all the plugs and connections. I will give you feed back. Thanks again
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