Cylinder 3 & 4 Cold at Idle - Wrist Twisters
 2Likes
  • 2 Post By umfri077
 
Thread Tools Display Modes
post #1 of 17 Old 04-21-2016, 09:28 PM Thread Starter
Tirone
 
Join Date: Apr 2016
Location: Martensville
Posts: 9
Rep Power: 1
 
Cylinder 3 & 4 Cold at Idle

Hi! I'm new to the forum and have read some great stuff here. I'm hoping to contribute and get some help as well!

I did some spring maintenance including valve clearance check and pull throttle cable replacement. These two jobs included removing the spark plug leads and also the vacuum hoses into the throttle bodies for cylinders 3 & 4 to gain better access to the throttle drum. Started it up, and didn't sound right. Rode it a few days, and eventually realized that cylinders 3 & 4 weren't firing at idle. Bike ran perfectly normal at anything above about 4K. All 4 headers hot after a highway ride. Since the bike ran fine when put away last fall (classic tale) I figured the problem must be related to something I touched this spring. Swapped plugs 1 & 4 - 4 still cold. Swapped lead 1 & 4, 4 still cold. Tonight on a whim I took off the vacuum hose for throttle body 4 and the bike runs great! All 4 firing at idle! My question is, what does this mean? I don't fully understand the vacuum hose routing. Does this mean I have a blockage in vacuum hose 4 (the one I took off)? Why would it run correctly now? Looking for the next step to take. Thanks!

umfri077 is offline  
Sponsored Links
Advertisement
 
post #2 of 17 Old 04-21-2016, 09:44 PM
Tesserarius
 
Nickr919's Avatar
 
Join Date: Oct 2013
Location: Corona
Posts: 734
Rep Power: 1
 
Look into your coil packs first. Just check all the connections into & out of them. Easy as that.

Nickr919 is offline  
post #3 of 17 Old 04-21-2016, 09:52 PM Thread Starter
Tirone
 
Join Date: Apr 2016
Location: Martensville
Posts: 9
Rep Power: 1
 
Coils are good - since all 4 cylinders are now firing. Also, the initial problem was split between the two coils since it was 3 & 4 with the issue (served by different coils). Pretty sure they can be ruled out as the problem.

umfri077 is offline  
 
post #4 of 17 Old 04-22-2016, 09:41 AM
Tesserarius
 
CKutz_GO's Avatar
 
Join Date: Feb 2014
Location: Frederick
Posts: 607
Rep Power: 1
 
I'm not really familiar, but i'll just throw it out there.. maybe your hose was pinched somewhere. It has to be able to flow air back and forth i believe or it would put the system under vacuum like your finger over a straw... right? maybe? maybe i have no clue what i'm talking about.. probably.
put it back on and see if it runs right.

CKutz_GO is offline  
post #5 of 17 Old 04-22-2016, 10:16 AM
Ian
 
HeliMech's Avatar
 
Join Date: Jul 2009
Location: Nova Scotia, Canada
Posts: 3,313
Rep Power: 1
 
Possible its the FPR?

The Fuel Pressure Regulator (FPR) draws vacuum off 3&4 through those hoses. Vacuum pulls the FPR diaphragm open allowing fuel to the injector rail... when the diaphragm fails it allows unmetered fuel into the 3&4 intake causing a rich condition and cold cylinders at idle and lower RPM.

HeliMech is offline  
post #6 of 17 Old 04-22-2016, 10:16 AM
Ian
 
HeliMech's Avatar
 
Join Date: Jul 2009
Location: Nova Scotia, Canada
Posts: 3,313
Rep Power: 1
 
Do the vacuum lines smell of fuel?

HeliMech is offline  
post #7 of 17 Old 04-22-2016, 04:52 PM Thread Starter
Tirone
 
Join Date: Apr 2016
Location: Martensville
Posts: 9
Rep Power: 1
 
Hmmm, FPR draws off of 2 & 3 not 3 & 4, so I don't believe it's the FPR. And none of the vacuum lines smell of fuel that I noticed. It's probably worth a check though to pull off the vacuum line right at the FPR, as it sounds like that's the best way to check it.

Ok, so an update after some fiddling in the garage this morning: As mentioned before, when pulling vacuum hose #4 off, all cylinders fire (confirmed by grabbing headers) when just letting the hose dangle. However, when I put my thumb over the removed hose, which is clearly pulling a good vacuum, cylinder #4 will die again (appears #3 actually is firing but warms its pipe a little slower than #1 and #2). I then tried the same exercise on throttle body #1. Pull off the vacuum hose, and all cylinders fire when letting vacuum hose #1 dangle. Put my thumb on vacuum hose #1, and cylinder #4 dies again. So putting my thumb over either a disconnected #1 or #4 hose gives the same symptom of #4 not firing as if you have all hoses properly connected. I should also add that when I put my thumb over the vacuum nipple on throttle body #4 (or on #1 nipple when doing that test) the bike is unaffected at all. So in summary, cylinder #4 will fire at idle only when the vacuum system is open to atmosphere at some point, but doesnít care whether its own nipple is plugged. Iím at a loss as to what this means at the moment. No FI codes have been thrown. I guess it means itís a system problem since it didnít matter if the #4 nipple was plugged or not?

umfri077 is offline  
post #8 of 17 Old 04-22-2016, 05:08 PM Thread Starter
Tirone
 
Join Date: Apr 2016
Location: Martensville
Posts: 9
Rep Power: 1
 
Shared this problem w/ another friend via email, and here's what he said:

"I'm wondering if removing the vacuum hose is allowing enough air to enter to compensate for the butterfly that is closed too far. So the vacuum leak is actually helping you."

It's plausible. There's a cryptic phrase in the service manual that says "don't allow the throttle drum to snap from full open to full close when the throttle cable is removed or it could result in a poor idle". It's not clear exactly what damage that would cause. I'm pretty sure I did let that happen when replacing the throttle cable though. How is that worse than someone who just releases the twist grip suddenly though? Could you actually throw an individual butterfly off its correct angle?

umfri077 is offline  
post #9 of 17 Old 04-22-2016, 05:25 PM Thread Starter
Tirone
 
Join Date: Apr 2016
Location: Martensville
Posts: 9
Rep Power: 1
 
haha - sorry to post on my own thread 3 times in a row. Trying to work through the logic of what I've found is driving me nuts. What my friend said can't be it. Putting my thumb over the vacuum nipple while the hose was off didn't make anything worse. All 4 fire when the vacuum system is open to atmosphere, regardless of what I did to the nipple. So it's no so much that #4 is dying for more air, more that the MAP is working better at higher pressure?

umfri077 is offline  
post #10 of 17 Old 04-23-2016, 09:53 AM Thread Starter
Tirone
 
Join Date: Apr 2016
Location: Martensville
Posts: 9
Rep Power: 1
 
SOLVED!! Turns out when I removed the two vacuum hoses from throttle body #3 to access the throttle drum to replace a cable, I reinstalled the FPR vacuum hose on the MAP vacuum hose nipple! So just a heads up to anyone having the same issues, the two nipples on the throttle body must not be routed identically within the throttle body. Woo hoo!
LDH and Jonstrocity like this.

umfri077 is offline  
post #11 of 17 Old 04-25-2016, 07:25 AM
(Quintus) Pilus Prior
 
badmoon692008's Avatar
 
Join Date: May 2013
Location: Neenah, WI
Posts: 2,218
Rep Power: 1
 

Awards Showcase
Extraordinary Ride 
Total Awards: 1

Quote:
Originally Posted by umfri077 View Post
SOLVED!! Turns out when I removed the two vacuum hoses from throttle body #3 to access the throttle drum to replace a cable, I reinstalled the FPR vacuum hose on the MAP vacuum hose nipple! So just a heads up to anyone having the same issues, the two nipples on the throttle body must not be routed identically within the throttle body. Woo hoo!
always nice to see a happy ending!

Love is the feeling you get when you like something as much as your motorcycle - Hunter S. Thompson
I just mı̸̸̸̸̸̸̸̸̸̸̸̸̸̸̸̸̨ade you wipe your screen.
-2009 Suzuki GSX-R 750 Race Bike
-2007 Honda 919
-1995 Nighthawk 750 (Tboned)
-1983 KZ 440 (Sold)
badmoon692008 is offline  
post #12 of 17 Old 04-25-2016, 09:20 AM
Fool in the Rain
 
HondaJim's Avatar
 
Join Date: Feb 2006
Location: Louisville, Kentucky
Posts: 10,284
Rep Power: 1
 
Garage

Awards Showcase
Donation Wrist Twisters Event Attendance Extraordinary Ride Wrist Twisters Event Attendance 
Total Awards: 4

Quote:
Originally Posted by badmoon692008 View Post
always nice to see a happy ending!
TWSS.

"Towards the end of the vid, it looks like she may have had a bafflectomy." - MarylandMike
HondaJim is offline  
post #13 of 17 Old 04-25-2016, 08:00 PM
Discen
 
hondatech9's Avatar
 
Join Date: Mar 2016
Posts: 225
Rep Power: 1
 
I was reading thru this and thought there might be a crossed line somewhere. Good going !!

When I'm dealing with multiple vacuum lines I like to have a bunch of different color sharpies or paint markers on hand and put a little dot on the nipple and corresponding hose color coded so I know which hose goes where. Dot the end of the nipple and the face of the end of the hose and when everything goes back together, you won't even see a bunch of colored dots everywhere. Nice and clean.

hondatech9 is offline  
post #14 of 17 Old 02-07-2017, 09:51 PM
Tirone
 
Join Date: Feb 2017
Posts: 3
Rep Power: 1
 
Quote:
Originally Posted by umfri077 View Post
SOLVED!! Turns out when I removed the two vacuum hoses from throttle body #3 to access the throttle drum to replace a cable, I reinstalled the FPR vacuum hose on the MAP vacuum hose nipple! So just a heads up to anyone having the same issues, the two nipples on the throttle body must not be routed identically within the throttle body. Woo hoo!
Hi there,
I having an similiar issue as you, cold #3 and #4
may I ask you what does it mean of" the two nipples on the throttle body must not be routed identically within the throttle body"?
Thanks

mare is offline  
post #15 of 17 Old 02-08-2017, 12:20 PM Thread Starter
Tirone
 
Join Date: Apr 2016
Location: Martensville
Posts: 9
Rep Power: 1
 
Quote:
Originally Posted by mare View Post
Hi there,
I having an similiar issue as you, cold #3 and #4
may I ask you what does it mean of" the two nipples on the throttle body must not be routed identically within the throttle body"?
Thanks
I just meant that one nipple on the throttle body must lead to the space behind the butterfly while the other must lead to the space in front of the butterfly (different air pressures). If both nipples lead to the same place, there would have been no difference in the bike's behaviour when I swapped them. I've never had the throttle body assembly off the bike to verify this, but it's the only explanation I can think of.

So in your case, it would be worth pulling off the two hoses from the two nipples on throttle body #3 and putting them on each other's nipple. On mine, it instantly ran normally after doing this.

umfri077 is offline  
post #16 of 17 Old 02-08-2017, 05:58 PM
Tirone
 
Join Date: Feb 2017
Posts: 3
Rep Power: 1
 
Quote:
Originally Posted by umfri077 View Post
I just meant that one nipple on the throttle body must lead to the space behind the butterfly while the other must lead to the space in front of the butterfly (different air pressures). If both nipples lead to the same place, there would have been no difference in the bike's behaviour when I swapped them. I've never had the throttle body assembly off the bike to verify this, but it's the only explanation I can think of.

So in your case, it would be worth pulling off the two hoses from the two nipples on throttle body #3 and putting them on each other's nipple. On mine, it instantly ran normally after doing this.
Thank you for your reply/
You know what?
After swapping those 2 vacuum hose on #3, my 919 came back to life, ^^
Thank you for your great help.

mare is offline  
post #17 of 17 Old 02-09-2017, 06:27 AM Thread Starter
Tirone
 
Join Date: Apr 2016
Location: Martensville
Posts: 9
Rep Power: 1
 
Cool! Glad I could help!

umfri077 is offline  
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Wrist Twisters forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

 
For the best viewing experience please update your browser to Google Chrome