2007 vfr 800 vtec - cold start not working.

Hi guys, hoping you can help me out with this one - I have read the many threads on the problem but can't get mine fixed.

2007 bike, all standard.

Problem - won't fast idle from cold, a ba$tard to start (engine flooding and needing plugs pulling most times), runs fine the rest of the day once started.

Here's what I have done to her to try to cure it:

New plugs (Iridium)
New Air Filter (Genuine)
New Battery
Starter Valves Synched
TB's synched.
Valve clearances done.
Compression check - all good.
Plugged into Honda diagnostics - no codes
Harness pulled apart and block connectors cleaned.
Injectors serviced (Mr Injector) - all good.
Inlet Manifold Sensor checked.
MAP sensor swapped out.
ECT disconnected - no change.

It has now got to where she will fire and run at around 1100 rpm if started from cold WITH NO THROTTLE and climb to around 1300 once warm.

This improved situation has coincided with slightly warmer ambient temperatures.

If she won't fire and then needs some throttle, she will sometimes start, run on 2 or 3 cylinders and stink of unburnt fuel OR flood and need a strip and plug clean.

Here's where my head is at:

Intermittent weak spark problem allowing the plugs to be drowned when cold??? No evidence for that yet.

Cold start circuit not working seems obvious one - BUT the bypass valves appear to be fully open and the wax unit appears to shut them when warm. But she just won't rev easily when stone cold.

Is it just the bypass valves that control the cold start circuit or is another sensor (maybe Lambda?)adjusting the fuelling as well? I thought maybe the ECT but that doesn't seem to make a difference if unplugged or if in the circuit? She appears to be getting either too much fuel or not enough air. Or both.

Any ideas or some thoughts on what I have done so far would be great!

Whale

 

Is it the same spark plugs that foul out or random ones? Same plugs, I would suspect weak spark - faulty coil or spark plug. (I've never had luck cleaning a fouled spark plug)

Have you checked the IAT sensor in the air box?

 

I see where you are going with this, When she won't start, all the plugs are wet.

When misfiring, it is pretty random as to which pot(s) are affected.

Have tried to isolate a single dodgy pot but unsuccessfully.

Have checked the IAT (called it the manifold sensor in my original post) and it is within spec.

Whale

 

Sorted it!

I am ashamed to say it was a pretty obvious fix once the logic circuit in the brain cut in.

I simply adjusted the small nut on top of the plate that the wax unit uses to move the plungers on the by pass circuit and... Bang! She fired up and sat at 2,000rpm until warm and them settled to 1200rpm

I though I had tried this solution by manually moving the plate during the process but is possible that this was when the engine was flooded and the plugs wet so she would not start.

I have no idea why this problem would appear unless it came out of the factory on a borderline setting and some wear in the linkages has created a loose area.

Anyway, - sorted!

The moral of the story is that when walking down the street and hearing hoof beats, expect to see horses when you turn around and not zebra's. Think about it.....

Just need the rain to stop now and off we go.

Whale

 

awesome!!! my bike never really seems to high idle circuit like my friends bikes. it usually only does it when its below 50 or sat for a long time and cold out too. my friends bikes, and most cars for that matter, usually always high idle circuit when its on the first start of the day. so i always wondered about it. i think ill give the wax unit a few tuns next time im in that area. thanks!!!

 

About a 180 degree turn with the ratchet worked for me, not much at all.

Whale

 

I appreciate the follow up. Sounds like I'm in the same boat as Candy, it has to be pretty cold out for the high idle to kick in.

Where should one be looking for this? A picture would be great, but words will get me looking in the right spot.

 

Air box off, just behind the front two throttle bodies, right in the centre. Synch your chokes while in there..

Couple of good vids on you tube if you search as well.

Whake

 

Sweet, thanks much.

 

Hey guys, my first post here. Can someone tell me if there is a picture of this wax thing quoted here "small nut on top of the plate that the wax unit uses to move the plungers on the by pass circuit and... Bang! She fired up and sat at 2,000rpm until warm and them settled to 1200rpm"

I'm seeing the same thing on mine.

Thanks gents!

 

This is the wax unit assembly Partytime.




And this is where it's located on your throttle body assembly. The airbox has to be removed to gain access to it.

 

Thank you sir. I wasnt able to see the pictures you attached, just red x's, but you got me going in the right direction.

 

I have a similar problem on my A6. It was fine in the summer but as the weather turned colder the bike just didn't want to fast idle. It starts fine everytime, but rattles and clunks until it warms a little. I shall have a play this weekend with wax unit.

 

Note to know of, if you have coolant coming out of "now-where" this is also the region to look, Mine had a small leak that was simply the hose clamp (spring type) was not on correctly so it would leak a bit, not enough to leave a puddle but enough to smell coolant and the odd drip or two on the garage floor.

 

I took the airbox off the bike today and had a look at the fast idle unit. I started the bike from cold and watched it operate. Of course it behaved perfectly. Just as an experiment I tightened up the adjustment screw slightly once the bike was warm but not enough to alter the idle speed, just to take some slack out.

One thing I did notice, the intake trumpets are two different lengths. The two long items were on the rear cylinders. The official manual doesn't mention this. There are two marks on each trumpet so I arranged the trumpets so these marks all faced each other.

I also painted the top yoke. The previous owner wasn't too concerned about scratching the triple clamp.


sent via fax machine

 

The longer trumpets are on the back pair because the airbox design feeds air in from the front. The trumpets are not needed but do increase flow rate to those cylinders due to the longer runner length. Down side it that those two cylinders go rich on all off idle movements. This is because it takes a little time to get the air speed to change on longer runners. This also means that they go briefly lean on throttle close as the air is still moving and will/does get by the throttle plate.

While you are in there get/make a manometer and balence/sync the starter valves. Make sure the starter jets open fully and are crud free.

Pair system delete is optional as it doesnt help or hinder anything. Evap system is also another if you really are looking to shave weight and complexity. Just make sure you either block off the lines that go to the tank and vacuum tree or get a vacuum control solenoid and wire it into the purge wires then connect the two lines to it. (Ive done the former as I couldnt see the need to put my tank under negative pressure.)

 

Thanks for that. I'll put the trumpets back where they were tomorrow. I've already done the pair mod. I found slow speed fueling was bad and did some research to find that fix. I tried the airbox flap too but it made little difference so reverted the change.

sent via fax machine

 

The flap mod doesnt do much and the gains just arent there. But taking the snorkel off does help and allows you to hear your bike a better mod would be if the two airbox inlets were plumbed into a longer runner out front so that they can get cooler air and ram forcing. Will need a bug screen of course, especially up hear where the bugs get the size of small birds!
By having both have their own runner out front you get the advantage of the flap actually adding volume to the runner and by closing it changes the runner flow speed. This would give the bike a better performance curve at speeds over about 15mph.

More things to think about and engineer

 

It seems there is quite a difference of opinion on the arrangement of the velocity stacks in the various VFR forums. I think I'll leave them as they are and see how the bike performs.

sent via fax machine

 

I tried several combos including no stacks. No real difference in how the bike performs, I ended up going back to factory as theres was no reason to change.