'06 800 cold starting weird behaviour...

Hi everyone, I've searched for solutions on this but no joy. Does anyone know why this happens: starting the bike in cold weather (less than 10 centigrade) the engine fires, runs for a few seconds at 1200rpm, then slows to 900rpm for about 15-20 seconds then gradually speeds up to 2500rpm. Idles at 1500rpm when warmed up and otherwise runs fine thereafter. Sometimes however, the bike will stall at 900rpm, and then be impossible to restart. It will fire a bit, but not pick up and run. The plugs are usually wet when removed, and after drying the bike will start and run again. I put a new set of plugs in previously when this started happening. Also, unless I wait for the bike to warm up to about 65-70 degrees, attempting to drive while the fast idle is still in operation, as I let the clutch out in first gear the revs will rise to 4000rpm with no throttle input from me. The Honda dealer (Dobles in Coulsden) I bought the bike from told me that "there is an issue with the VFR800 vtec that Honda won't acknowledge. The revs rise like that unless the bike is warmed up before you ride it." I smelt BS but let it go. He told me that they had put a genuine Honda air filter in ("they don't like pattern filters") and had tightened the little nut on the fast idle wax unit. A month later and it's still doing it, and last Friday it stalled and wouldn't start again. As I was away from home I bought ANOTHER new set of plugs (££££) put them in (1 hour in a freezing pub car park in the snow in Leicester) and it fired up. Honda are now saying it might be something to do with the TPS. I pointed out to them that the TPS cannot be bought separately so if it is the TPS it's going to be expensive and I ain't paying, and why didn't they discover that last time they "fixed" it? Grrr. Anyway, your knowledge on whether it's the FIWU/TPS/bad sensor would be much appreciated!

 

Starter valves my need to be synced.

I'd start there first.

Also ... you should let your bike warm to operating temperature before riding, especially in colder weather. Never rev above 4k until it's warmed up.

 

Your description sounds like an occasional mild over-fueling situation, occurring when the bike is at idle. And more specifically, it sounds like this over-fueling is being induced by intermittent erroneous input from one (or more) of the sensors. You didn't mention the ECM lighting up its "FI" light on the instrument panel with a blink-code so it seems your bike's malfunction isn't big enough (yet) to trigger that (I think the offending sensor would have to fail completely rather than just reporting erroneous data to the ECM).

All of the sensors on your 6th Gen are solid state electronics. They don't really "wear out", instead they last and last and last. Their primary point of vulnerability is the connector plug, and also of concern is the condition of their wiring. Another less common issue for a solid state sensor is the quality of the sensor's electrical path-to-ground (or even the entire bike's main path-to-ground). These sensors are calibrated to work properly with a good connection to ground, anything less than that will mess things up.

Have you done any modifications or add-ons to the bike's electrical system? Have you added items that would cause a higher than normal electrical system draw during startup or idle operation?

 

I agree with Greg that earth faults can lead to weird things happening.

On the other hand, the problem to me sounds like it is related to the wax unit/starter valves. I'd suggest starting there, specifically verify the hoses leading to the wax unit are clear and flowing coolant through the unit. After that you would want to verify that when warm (and by this I mean not stone cold but not at 80C either) the wax unit is not pushing the starter valves open, and the idle is being maintained by the idle adjuster screw. If all of those are OK then proceed to adjust the starter valves.

 

You guys are brilliant, thank you. I've got a nice clean used complete throttle body, and my heart is telling me to take the path of least resistance/hassle and bypass the Honda Stealership and get my local trustworthy mechanic to swap it in and check all the things you are flagging up...

 

Ps the bike is totally standard, no mods at all. I run a 2A fused Keis heated waistcoat and inner gloves off the (new) battery, but I only connect up when the bike is warmed up... I have also put a new reg/rec on.

 

Pps I synch'd the starter valves a couple of months ago.

 

Aha. I think I see what you're saying: if the starter valves are in any way open when the bike is warmed up, the ECU might get confused, hence the 4K rpm behaviour? If that's the case then the Honda technician made it WORSE and they lied to me about the "unacknowledged issue" (-they all do that, sir)... which still begs the hard starting question... hmmm. I guess Dobles have lost a customer.

 

Jeff, it's revving to 4K rpm without my input, all by itself

 

Yikes! Wish I could get my hands on it ... I do all my own work.

 

If you are seeing 4k rpm, then I'd say the wax unit is not correctly adjusted as it is the only thing that will allow the engine to rev that high without any throttle input.

When warm, the wax unit should not be contacting the starter valves, their resting position should be due to the idle adjuster only.

The wax unit is in the coolant circuit connected by small bore pipes; these can block up, and that can stop warming coolant reaching the wax unit, which then stays cold longer and keeps the idle high. I have read (on the ST1300 forum) that heat soak from the engine at a standstill eventually heats the wax unit up enough for it to allow the idle to drop, but when moving in cold weather the airstream can cause the wax unit to cool and bring the idle up again. So clearing the blockage in the coolant pipes/wax unit can correct that.

All of which assumes that the fault is not related to the TPS or other component...

 

Come on over, Jeff! Kettle's on...

 

Thanks Terry. The revs ONLY rise to 4K when it's in gear and I let the clutch out a few millimeters... if I pull the clutch lever back in to the grip, the revs drop back to what they were before, 2500rpm. It only does this until it's warmed up to about mid 60's C. After that, it's fine. So the revs are rising only with first gear engaged and clutch out, without me even TOUCHING the throttle. This is what the Honda dealer claims is a known fault that Honda "do not acknowledge".

 

A nice Earl Grey, please ....

I better start swimming now if I'm going to make it there before spring. Be good to see the relatives while I'm there.

 

Don't forget your goggles.

 

By the way... I think I already know the answer, but has anyone heard of this "unacknowledged by Honda" fault...?

 

Hmmm...the only thing that I know could cause what you describe is the clutch switch and the flapper mechanism in the airbox, for reasons known only to Honda the flapper is open in gear with the clutch in, but closed in gear with the clutch released. I've no concrete idea why that might change the idle speed. A complete guess would be that the flapper diaphragm is disconnected and/or the vacuum hose that drives it is open to atmosphere, so when the solenoid valve (which is controlled by the ECU in response to the clutch switch) opens to pull vacuum on the flapper, it allows an uncontrolled air leak into one cylinder?

To test that theory you can disconnect the clutch switch at the bar and see if the idle speed changes with clutch actuation then.

 

It's just far-fetched enough to work, you sir are a mad scientist.

 

One can also test the flapper mechanism in neutral on the centrestand, by disconnecting the neutral wire off it's post below the clutch cover. The ECU then assumes the bike is in gear even when it is really in neutral, and with the tank raised you can see the flapper operating at 5500rpm (closed below, open above), or at low revs with the clutch pulled in. Of course if the flapper doesn't move at all under these conditions, then my theory about the vacuum hose being disconnected or leaking might be confirmed.

 

I'm liking your "mad scientist" thinking. However, Honda repaired the flapper valve (or reconnected it) when they last had the bike, because it wasn't working. I'll try disconnecting the clutch switch, see if it still happens.