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Old 07-26-2002, 07:52 PM   #1
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Smile What functions does the cold start valve do?

What functions does the cold start valve do?
1982 928
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Old 07-26-2002, 08:49 PM   #2
Jack in Malta
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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.
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Old 07-27-2002, 12:23 AM   #3
Dennis Wilson
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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.

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Old 07-27-2002, 12:45 AM   #4
joel roeder
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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.
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Old 07-27-2002, 01:09 AM   #5
Dennis Wilson
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kevin? am i done yet?

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

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Old 07-27-2002, 06:15 AM   #6
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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?
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Old 07-27-2002, 06:15 AM

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