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Help! Misfire in #4.


klipsedeville

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Hi guys, yet another VFR rebuild. A friend's VFR '04 had been parked for over 2yrs. He's decided to get back in the saddle.

 

We've been able to get the bike running after replacing crankshaft and rod bearings, plugs, new ccts and new SC project exhausts.

 

However, the bike runs horribly on all for plugs, makes a bang sound and idles roughly. The revs do not come down if you blip the throttle when the bike is warm. But here's when it gets funny, if you disconnect #4 spark plug, it runs smoothly, but you can hear popping in the exhaust due to unburnt fuel.

 

No FI lights... But I can hear a clicking sound like a vacuum leak.

 

I've attached audios. You can hear when #4 plug is connected and disconnected.

1095050986_30Sep11.08.aac 30 Sep, 11.14​.aac

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Sounds terrible!

 

Have you confirmed with all the work done that the Injectors and Ignition coil plugs are on their correct positions? They can be identified by a single wire colour code for each plug. (refer your wiring diagram).

 

Injectors. Cylinders..

1= Pink/Blue.

2= Red/Yellow.

3= Pink/Green.

4= Pink/Black.

Ignition. Cylinders..

1= Blue/Black.

2= Yellow/White.

3= Red/Blue.

4= Red/Yellow.

 

Another thing to check for unburnt fuel is the Fuel Pressure Regulator for a ruptured diaphragm. This will dump excess fuel into cylinders 3 and 4 via the vacuum hoses causing terrible running. Check for any signs of fuel in the FPR vacuum hose or dripping fuel from the FPR vacuum connection.

 

With a bike parked for over two years the injectors may have gummed up and require some professional cleaning and flow balancing.

 

Assume your cam timing is exactly correct!

 

Good luck.

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6 hours ago, Grum said:

Sounds terrible!

 

Have you confirmed with all the work done that the Injectors and Ignition coil plugs are on their correct positions? They can be identified by a single wire colour code for each plug. (refer your wiring diagram).

 

Injectors. Cylinders..

1= Pink/Blue.

2= Red/Yellow.

3= Pink/Green.

4= Pink/Black.

Ignition. Cylinders..

1= Blue/Black.

2= Yellow/White.

3= Red/Blue.

4= Red/Yellow.

 

Another thing to check for unburnt fuel is the Fuel Pressure Regulator for a ruptured diaphragm. This will dump excess fuel into cylinders 3 and 4 via the vacuum hoses causing terrible running. Check for any signs of fuel in the FPR vacuum hose or dripping fuel from the FPR vacuum connection.

 

With a bike parked for over two years the injectors may have gummed up and require some professional cleaning and flow balancing.

 

Assume your cam timing is exactly correct!

 

Good luck.

I quickly tested the FPR as you've suggested and it checks out, no leaks. However, I noticed that if I block the 2 idle air intake holes on #4, the bike runs smoother. If I attempt blocking the holes of any of the other cylinders, the bike dies. And i can feel the vacuum from the holes are a lot stronger on all 3 cylinders. (placing my finger over the holes). I can feel it suck on my finger stronger. #4 is weak, barely any sucking. Is this a vacuum leak somewhere or a blocked vacuum hose?

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Just to clarify, by "idle air intake" do you mean the small holes for the starter valves?   Or the whole intake above the throttle gate valve?

 

If starter valve, check the linkage and actuation of the starter valves and fast idle wax unit.  
 

The starter valves are only supposed to be open or mostly open when the bike is cold, and the wax unit is holding them open.  As it warms up from coolant it should close them down.  
 

If its not the starter valves then their vacuum is coming from the cylinder right below it and the number of "good" causes for low vacuum on one cylinder start to dwindle here.  Since you did rods and bearings I assume you would know if you had bad rings or something, etc.  like Grum says, timing maybe...

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Have you tried synching the starter valves or using a vacuum gauge set? From your finger test it certainly sounds like #4 is getting weak vacuum which probably means an air leak, either the throttle boot (cracked? loose? not seated?), or one of the rubber vacuum hoses, or possibly the starter valve just needs adjusting (closing down a bit). Could also be some crud/corrosion on the throttle butterfly plate causing it not to seal.

 

On the FI bikes, the butterflies should be fully closed at idle, all air for idle running passes through the starter valves, and these are always open (otherwise you'd have no idle) and they get pulled further open by the wax unit when cold. When hot, the wax unit should be letting the starter valves rest on the idle screw. 

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Addition to all the swell advice I'll ante up my RC45 notes... Honda's race bred V4 employs a manual idle adjustment and a manual "CHOKE" instead of the automatic wax...

 


For the system to work as designed on start up the butterflies must be 100%
closed... this is because close butterflies equals sufficient vacuum... without
sufficient vacuum the fuel cannot be drawn into the combustion chamber to
support start up... the result is hard starting... the drill for cold or hot start is

   

1 100% close throttle for sufficient vacuum
2 Full choke when cold no choke when hot
3 Hit start.

 

The dead give away of an air leak on a Fi engine is high uncontrolled
idle... on a fuel injection system *any* air that gets past the
throttle bodies the map just adds the corresponding fuel... the result
is high uncontrollable idle... make sure all the rubber hoses are
connected and in good shape... make sure all the intake boots are
tight and in good flexible shape... if the rubbers are hard and
cracked its time for replacement...

 

 

gallery_3131_51_651212.jpg
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11 hours ago, ShipFixer said:

Just to clarify, by "idle air intake" do you mean the small holes for the starter valves?   Or the whole intake above the throttle gate valve?

 

If starter valve, check the linkage and actuation of the starter valves and fast idle wax unit.  
 

The starter valves are only supposed to be open or mostly open when the bike is cold, and the wax unit is holding them open.  As it warms up from coolant it should close them down.  
 

If its not the starter valves then their vacuum is coming from the cylinder right below it and the number of "good" causes for low vacuum on one cylinder start to dwindle here.  Since you did rods and bearings I assume you would know if you had bad rings or something, etc.  like Grum says, timing maybe...

Yes the starter valve holes. I watched the wax unit slowly close. The rings looked like they were in good shape for all cylinders. My friend never complained of burning oil or smoke from exhaust to indicate rings. The bearings were quite complicated to do, we had to read the chart from the manual over and over before we understood how to get bearing size (color) for each rod and crank. Would a compression test on that cylinder indicate bad rings?

 

I believe the cams are timed, followed the manual as usual, cam index lines match up with 4T/ :|F 450deg after 3T/ :|F

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7 hours ago, Terry said:

Have you tried synching the starter valves or using a vacuum gauge set? From your finger test it certainly sounds like #4 is getting weak vacuum which probably means an air leak, either the throttle boot (cracked? loose? not seated?), or one of the rubber vacuum hoses, or possibly the starter valve just needs adjusting (closing down a bit). Could also be some crud/corrosion on the throttle butterfly plate causing it not to seal.

 

On the FI bikes, the butterflies should be fully closed at idle, all air for idle running passes through the starter valves, and these are always open (otherwise you'd have no idle) and they get pulled further open by the wax unit when cold. When hot, the wax unit should be letting the starter valves rest on the idle screw. 

the #4 cylinder is the static one as reference for the other 3...😢 I sprayed around the boot and no sign of a leak, engine sound didn't change either. 😭😭

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Do you know if the airbox flapper is still attached ? Plus the flapper vacuum control valve ? Is the pressure sensor MAF hose attached at rear right corner of the airbox ? Both of these T into the starter vacuum hoses. And are all 4 vacuum tap hoses attached to their blocking stubs on the sides of the airbox ? 

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Good news! I found the problem and it was not what we were thinking 😃. Going with the popping exhaust I figure fuel was dumping in the exhaust so I decided to look at the exhaust valves maybe they werent sealing properly. See picture...

 

SAVE_20221002_195658.thumb.jpg.68d48552dbff7e7a0d30807bf550dc48.jpg

Took out the cylinder and noticed that the bucket wasn't flush, it was almost as high out as the VTEC valves. Removed it and the shim was dislodge with the clip!

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14 hours ago, klipsedeville said:

 

What could have caused that to happen?

 

 

Sometimes life throws you a curve ball...

 

20220920_155508_copy_2880x2156.thumb.jpg.841ce6789679ce5f29de58e25a89ba70.jpg

(Or you choose to go look for one :tongue:)

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Pic seems to show missing keeper/cotter piece on top of valve stem, where could it go assuming the bucket/shim above?maybe there was only ever one @ original assembly, which worked ok until the over-rev? Curious the valve didn’t drop low enough to smash piston catastrophically...

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