C28 / STVA problems

Hi,

I have a problem with my SV650SK6. Since I got it a few months ago the FI light has come on intermittantly, always with code C28. Most of the time it's ok riding with the code, although sometimes it's very low on power (presumably the secondary throttle valve is closed). A couple of times it's felt quite dangerous, once trying to get up to speed with lots of traffic around and once having to abort an overtake. Sometimes the code disappears while I'm riding along, mostly I stop and turn off/on to try to clear it. I've not had the symptom other people have described of the bike revving with closed throttle.

If I remove the airbox and turn on the ignition sometimes the self-check (STV full open then partial open) works fine, but other times it just messes around opening and closing or "quivering". Sometimes the self-check seems to work ok then after a few seconds it starts moving back and forth a little bit.

I've checked according to the FI system diagnosis PDF, as far as I can see everything checks out. I'm not entirely sure how best to check for poor contacts in the connectors, I've tried checking resistance of the STVA from the ECU connector and that seemed ok. Also tried adjusting the STV position sensor in case this could cause the issue but that didn't seem to help. If the STV position sensor was out I'd also expect that to give a different code.

I asked an independent dealer to take a look while they had the bike for something else but they recommended that I either take it to a Suzuki dealer or change the STVA. Based on the cost of second-hand throttle bodies vs. cost of labour, I bought some TBs off eBay, but the same thing happens with these, or at least the self-check is still messed up.

The only things I can think of from here are:

1. Give in and take it to the Suzuki dealer.
2. Buy a second-hand ECU from eBay and give that a try.
3. Splice in a new set of wires from the STVA connector to the ECU.

I know this is an issue that's come up before, but I've not found any threads that match my symptoms where there's a solid conclusion. Apologies if I've missed one.

Does anyone have any suggestions before I start throwing more money at this...? Can Suzuki dealers test the ECU somehow? Has anyone seen this problem caused by a faulty ECU?

Cheers,

Ben

[Sid Squid]

If you've checked continuity of the relevant wires and security and condition of connectors, and found no problem then it would seem that there is a component problem, but bearing in mind that wiring and connector faults account for the overwhelming majority of electrical and electronic problems that I am presented with, in your position I would make utterly certain that all those parts are tip-top before spending money on possibly un-necessary parts. After that, is it possible that you could find a friendly forum member whose ECU etc. could be substituted to identify the problem?

Thanks for coming back to me so quickly. It sounds like I need to check the connectors again more thoroughly. I'll test the resistance of the STVA from the ECU connector again, as I'm guessing that should be a good test of the two connectors near the STVA. I'm less certain of how to test the ECU connector however.
If any of these connectors are at fault, is there any way to replace them, or is it a matter of trying to bend the terminals to get a better connection (or a new loom)? I can't see any obvious corrosion, but I will check that again as well.

I wondered about checking the output from the ECU with the ignition on (e.g. needle probes from the back of the connector) but I'm guessing it may not be easy to measure using just a multimeter?

Cheers,

Ben

[Red ones]

What's the weather like when it happens? It doesn't happen to be damp by any chance?

Also does it ever hold the revs too high when you are riding? (Which is scary if your going in to a corner as the guy I know was at Snetterton!)

[Sid Squid]

There is - I think - a voltage check across the STVA, I'll look it up.

[Red ones]

I have only just spotted the comment "Splice in a new set of wires from the STVA connector to the ECU"

Have you spotted the connector on this line? It's a small black box. I'd open it up and check the state of the connections in there, for what it's worth.

I generally only take the bike out when it's dry, and it's been sat in my garage for about a week, so unless it's some trapped moisture I don't think it's damp. I may try blowing the connectors out with an airduster tomorrow though, just in case. The guy who owned it before me used it in all weathers I think, which may explain the less than ideal condition.
I've certainly not noticed it holding the revs too high, although I did note other people had said theirs did that. I must admit I was confused as to how that could happen - one set of throttle butterflies is controlled by the rider, so surely shutting that will close off the airflow even if the STV is wide open? I may be missing something obvious here...

So in terms of connectors I've looked at, there's the one that connects to the STVA itself, then a connector from the STVA-and-injectors sub-loom to the main loom, then the connector from the loom to the ECU. Am I missing one...?

Sid - thanks for taking a look.

[Sid Squid]

Disconnect the plug at the servo, and on the servo's terminals check for continuity between the terminal that the red/black wire connects to and a convenient earth point, there should be none. Then check resistance across the two terminals of the servo, which should be between 7 and 14 ohms. Reconnect the servo plug and disconnect the ECU connector and do the same checks at that point - red/black wire to earth and across red/black to black/red wires. Obviously this should give the same results as at the servo, if it doesn't then there's a wiring/connector fault.

Ok, so as far as I can tell there's no continuity between that terminal and earth. Resistance across the servo is around 10 ohms, and it's similar when tested at the intermediate connector and at the ECU connector (slightly higher resistance moving away from the servo). I tested a couple of times and the numbers varied slightly (less that 1 ohm) but this may have been down to the connection from the multimeter probes to the connectors.

Once I'd reconnected it all back up, I turned the ignition on and the STV was moving about all over the place, back and forth, definitely not the normal self-check movement. No C28 code though, just various other codes which I assume are because the airbox is off.

Just to check I'm not being a complete idiot, the throttle bodies are sitting loose at the moment, as I wanted to test before I reattached them, and because it's a lot easier to access the servo terminals. I'm thinking this should be ok, because they're connected via rubber normally i.e. not earthed?

Anyhow, based on these results my best guess is that either the ECU connector terminals aren't contacting the ECU pins properly, or the ECU is bad. I'll have another check tomorrow evening if I get time.

[Red ones]

Sounds like the problem I had last year.
http://forums.sv650.org/showthread.php?t=201511

Eventually I sold the bike, but the next owner fixed it. The cabling from the STVA was corroded in a connector block.