What functions does the cold start valve do? - Rennlist - Porsche Discussion Forums

Go Back  Rennlist - Porsche Discussion Forums > Water Cooled Technical Discussion Areas > 928 Forum
Reload this Page > What functions does the cold start valve do?
Notices
928 Forum
Sponsored by: 928 Specialists

What functions does the cold start valve do?

Reply

Old 07-26-2002, 06:52 PM
  #1
lacast
User
Thread Starter
 
lacast's Avatar
 
Join Date: Jul 2002
Location: South Texas
Posts: 71
Smile What functions does the cold start valve do?

What functions does the cold start valve do?
1982 928
lacast is offline  
Reply With Quote
Old 07-26-2002, 07:49 PM
  #2
Jack in Malta
User
 
Join Date: Jul 2002
Location: Malta
Posts: 139
Post

Hi

I have a 1982 Euro. The cold start is active for a few seconds when you start the car and it supplies a controlled burst of fuel into the intake which should ensure the car fires as as to the best of my knowledge the injectors do not open initially. If its blocked it will cause starting problems and if it is leaking it will cause mixture and pressure problems.

Why do you ask?

I initially had a wiring problem that led to the cold start only working occasionally.
Jack in Malta is offline  
Reply With Quote
Old 07-26-2002, 11:23 PM
  #3
Dennis Wilson
Super User
 
Dennis Wilson's Avatar
 
Join Date: May 2001
Location: Owasso, OK
Posts: 2,747
Post

The cold start valve functions the same as a choke, in that it provides extra fuel when your engine is cold. Its duration of operation is from 2 to 12 seconds. As Jackin mentioned, if it leaks it can cause difficult cold and hot starts. Its power is supplied through the thermotime switch.

Dennis
Dennis Wilson is offline  
Reply With Quote
Old 07-26-2002, 11:45 PM
  #4
joel roeder
User
 
Join Date: Jun 2002
Location: georgia
Posts: 40
Post

cold start valve function is the enitial shot of fuel to start cold engine. once you start the warm up regulator can take up the slack in so far as running a richer mixture during cold engine warm up. (cold start enrichment). the cold start valve is run by the thermo time switch, this temp sensor regulates the time the cold start valve stays open or turns on at all. tha cold start enrichment sets a lower fuel control presure at the fuel distributor allowing injectors to run richer, as the engine heats and the electrical signal to the warm up regulator warms it, the control presure increases to lean the fuel system to run with the warmer temps. O2 sensor cars had another temp sensor that controled when the lambda seystem would start. alot of the sensors were set too warm and were allowed to work on a cold engine on a warm day. this caused hesitations and poor proformance. a bad cold start valve causes longer cranking time and no start at all in cold weather. a bad warm up regulator will give same complaints as o2 circut falty but lasts longer. a fuel presure guage is the best way to diagnose fuel issues on a cis system. a noid lite for bosch injection is also a good tool. on the electrical side the most common issue is either the thermo time switch or the power sorce. many times on these systems the power sourse is tied in as a secondary circut on a relay such as fuel pump or lambda relays. so part of the relay works and another doesnt, hard to find problem at times but not uncommon.
joel roeder is offline  
Reply With Quote
Old 07-27-2002, 12:09 AM
  #5
Dennis Wilson
Super User
 
Dennis Wilson's Avatar
 
Join Date: May 2001
Location: Owasso, OK
Posts: 2,747
Post

kevin? am i done yet?

Kevin, you left out the auxillary air regulator and the frequency valve on O2 systems. 8^)

Dennis
Dennis Wilson is offline  
Reply With Quote
Old 07-27-2002, 05:15 AM
  #6
jpitman
User
 
Join Date: Nov 2001
Location: Riyadh
Posts: 243
Post

There are several parts to 'cold start'
1. Thermo time switch allows current through if temp is below X (for up to 12 Secs) to an injector to supply extra fuel for rich mix.
2. WUR in CIS, or a temp sensor in EFI allows richer mix which gradually fades to normal for a minute or two (depends on ambient temp).
3. Extra air valve in CIS, L-jet allows more air than normal to provide a higer idle to stop stalling. In LH, the Idle control valve lifts idle until warmed up.
I think thats all?
jp
jpitman is offline  
Reply With Quote
 

Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
traxtar928
928 Forum
14
07-20-2016 05:11 PM
Handy930
911 Turbo (930) Forum
8
12-04-2012 06:57 PM
Tripster
911 Turbo (930) Forum
20
05-24-2006 09:45 PM
FLYN930
911 Turbo (930) Forum
8
04-05-2006 03:21 PM
Hladun1
911 Forum
7
01-12-2002 06:24 PM


Thread Tools
Search this Thread
Posting Rules
You may not post new threads
You may not 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

Forum Jump


All times are GMT -3. The time now is 02:25 PM.


Copyright ę 1998 - 2017 Rennlist.com
 
  • Ask a Question
    Get answers from community experts
Question Title:
Description:
Your question will be posted in: