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Discussion Starter · #1 ·
Last year I had this error and found one of the soldered terminals in the STVA was disconnected. For those who don't already know I have a 2006 C50T, DJ drive mod, oem K&N replacement air filter in the football, stock exhaust with honest Abe mod. I am getting the fi error code 28 again. Using Clymers to troubleshoot...All steps checked out ok except for the second step, the operation test. According to the test in ch 9 the valves are supposed to close fully then fully open then

go the normal operating position (about 95% opened). Here's what mine does...full open then jirk a little. So I concluded a failed test. Everyone agree? Now, the suggestions for this condition are:

1. Loose or corroded terminals in the STVA connector.
None found, all good.

2. Open or short on the pink and black wires or on the white/black and green wires in the harness.
None found, all good.

All the remaining steps in the troubleshooting guide were satisfactory. So I'm left scratching my bald head. When I start the engine it fires right up and idles fine. In a moment the fi lights up, still runs fine idling but at times lacks power to quickly accelerate. It will accelerate just not like it should. This is only while the light is on. If I start and ride it goes like it should until the light comes on.

Any ideas?


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If you only pray when you're in trouble...you're in trouble.
 

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Do the secondary throttle valve butterflies close easily -all the way by hand?

The linkage on the left side can foul and make resistance to movement keeping them from closing as they should. That set the 28 code on mine.
 
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Discussion Starter · #4 ·
Do the secondary throttle valve butterflies close easily -all the way by hand?

The linkage on the left side can foul and make resistance to movement keeping them from closing as they should. That set the 28 code on mine.
What do you mean "foul"? Did you lube the linkage then or ???
 
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Discussion Starter · #5 · (Edited)
I've got the STVA off and apart all connections inside are intact. Shouldn't this motor actually turn when powered? It jerks a little and I can hear it hum, like a motor that wants to turn but can't.
 

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The starting position that is assumed when the key is turned to ''on'' is determined by the stv sensor....

If you move the STV plate to the closed position, does it move to the same position each time the key is turned to ''on''?


Yes the linkage on mine seized with oil and dirt and wouldn't move. I thought the actuator was seized until I took it off and the plate still wouldn't move.

It started out as an intermittent problem and finally, one day, seized solid on a trip to visit the inlaws....
 
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Discussion Starter · #7 ·
Yes it did always return to the same spot, if it moved at all. Sometimes it just jerks and tries to move. With the STVA off the throttle body and the stv sensor still on it the same thing happens, it just jerks. I can easily turn the motor shaft by hand. This thing has really got me puzzled.
 
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Discussion Starter · #9 ·
This is removed from those plastic gears at the moment.
Cable Wire Electrical connector Technology Electronic component


But even while it was all assembled I was able to move the valve and no damage was done to the gears.
 
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Discussion Starter · #13 ·
I don't know why this didn't come to mind earlier in the discussion about manually moving the secondary throttle valve. To test the resistance of the stp sensor requires readings of both opened and closed positions. The manual instructs to "manually" move the valves to obtain those readings. If you have a Clymer manual refer to pages 252 and 253. See the pic below.


Text Font Document Paper
 

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From my Suzuki Service Manual

C28 is STV actuator circuit malfunction.

The operation voltage does not reach the STVA.

ECM does not receive communication signal from STVA.

"Possible Cause"....STVA malfunction, STVA circuit open or short, STVA motor malfunction.

1)Remove fuel tank

2)Ignition switch off

3)check STVA lead wire, loose or poor contact

4)remove air intake pipe

5) Turn ignition switch on check STVA operation....95% open....Full open...95%open.

If operation is not ok, loose or poor contacts on STVA coupler, or....

open or short circuit in the (P/W or black) and B/Lg or Green wires.
Then it goes into measuring resistance of the STVA wires. If they check good it continues...

B/Lg, P/W, Green and Black wire open or shorted to ground, or poor connection.

If wire and connection are OK, INTERMITTANT TROUBLE OR FAULTY ECM...

Recheck each terminal and wire harness for open circuit and poor connection.

REPLACE THE ECM WITH A KNOWN GOOD ONE, and inspect again.

If resistance is NOT ok, replace STVA with a new one.
 
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Discussion Starter · #15 · (Edited)
Thanks Viper, I'll use this to troubleshoot mine again. My STVA was behaving like your svc man said... 95% open 95%. The Clymer differs, it says closed, opened, 95%. Maybe I'm looking for something that is not going to happen. Never-the-less, I still have a c28 and don't know why, yet. I'm beginning to suspect the ECM but haven't found a reason to confirm that suspicion.
 

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It could be an intermittent short or open in the wire harness somewhere, a real beotch to find.

I was "stranded" in Hawaii for four days as we chased down a chaffed wire that was shutting down a fuel boost pump. We started chasing wires at the nose wheel well and found the culprit wire up on the backbone of the airplane by the tail.

Hawaii was nice though. :wayhappy:
 
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Discussion Starter · #17 ·
I had to laugh because I just assumed you (and your motorcycle) were stranded in Hawaii and I was going to ask how the ride was.:biglaugh:

Electrical problems are a nightmare. I broke down today and consulted a local dealer. After he insulted my intelligence I told him I would probably not be consulting him again.

Anyway, all the wires relating to this tested fine for continuity. I'm just not sure whether it's the STVA or the ECU or neither. I'm prepared to buy a new tb if needed but I want to be absolutely certain.
 

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LOL, no we were chasing wires on an F16 we were bringing back from Singapore.

That's the thing with an intermittent short, continuity can be good, turn the bike 180 and it can be bad.

Ask me about the time I mounted the tipover sensor upside down. :biglaugh:
 
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Discussion Starter · #19 ·
So, when the bike was right side up it shut off. It would only run on its side?

Two weeks ago while troubleshooting a flooding issue, I accidentally set mine on fire. I kinda wish I would have been a little slower at putting it out. But, no damage. Think I missed my opportunity?
 

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So, when the bike was right side up it shut off. It would only run on its side?

Two weeks ago while troubleshooting a flooding issue, I accidentally set mine on fire. I kinda wish I would have been a little slower at putting it out. But, no damage. Think I missed my opportunity?

Yup, that's about it. It would start and then would shut off in about 3 seconds, thought it was upside down.

Join the club, I had my '05 on fire for awhile.
 
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