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  #1  
Old 12-03-2022, 10:23 AM
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Location: Oklahoma
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'86 cold start valve issue (cold start problem)

Problem - my 1986 560SL won't start when cold. The colder it gets the harder - and longer - it takes. I can usually get it to start after cranking for several MINUTES!

Here's what I know after some early morning tests - it's currently 30F here and I decided to test the cold start valve. Pulled it and aimed it in a jar and it's not working - no fuel present while cranking....

Tested for voltage at the connector while cranking and I do NOT have 12 volts...

Tested the CSV directly by wiring a 12 volt source straight to the valve and when I do that the valve operates nicely - nice atomized flow of fuel present.

Clearly I have a problem getting electricity to the valve...

But, I can not find a wiring diagram for the cold start valve anywhere - I know it's connected to the coolant temp sensor, but I'm pretty sure I tested it the last time I went through this and it tested OK - but I don't know...

Any thoughts?

ryan

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RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE
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  #2  
Old 12-03-2022, 12:31 PM
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Join Date: Feb 2011
Location: Modesto CA
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-Power for the CSV comes through the fuel pump relay (FPR).
-The circuit for the CSV within the FPR is separate from the circuit for the pumps themselves. Hence, it is possible for the pumps to run without the CSV circuit closing.
-The temperature logic signal to the CSV circuit in the FPR is supplied by the engine control unit (ECU).
-Power to the CSV appears at pin 4 of the FPR.
-Power for the CSV circuit is supplied on pin 9 of the FPR, and comes from the overvoltage protection relay (OVP).
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  #3  
Old 12-03-2022, 06:30 PM
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First off - thanks for the help!

OK - if I'm following correctly, since I have no power to the CSV I have a problem at EITHER the FPR or the OVP. I know I have replaced the OVP recently with a new unit, so if the OVP is functioning properly I should have 12v at pin 9 of the FPR - if not, bad OVP - correct? Key On Engine Off or Key On Engine Running?

And if I do have 12v at pin 9, I should have 12v at pin 4 of the FPR (which is on its way to the CSV) - if not, bad FPR - correct?

If I have voltage at these connections, then I have a problem in the wiring from the FPR to the CSV - correct?

Am I missing anything?
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RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE
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  #4  
Old 12-03-2022, 07:13 PM
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Location: Modesto CA
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Quote:
Originally Posted by rgnprof View Post
First off - thanks for the help!

OK - if I'm following correctly, since I have no power to the CSV I have a problem at EITHER the FPR or the OVP. I know I have replaced the OVP recently with a new unit, so if the OVP is functioning properly I should have 12v at pin 9 of the FPR - if not, bad OVP - correct? Key On Engine Off or Key On Engine Running?
Correct, and Correct.

Quote:
And if I do have 12v at pin 9, I should have 12v at pin 4 of the FPR (which is on its way to the CSV) - if not, bad FPR - correct?
Power at pin 4 will be present only when cranking, and for a very short period immediately after start.

Quote:
If I have voltage at these connections, then I have a problem in the wiring from the FPR to the CSV - correct?
Correct.

Quote:
Am I missing anything?
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  #5  
Old 12-04-2022, 12:13 AM
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RG:

Also in the CSV circuit is fuse #7; check for integrity, clean contacts, continuity, etc.
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  #6  
Old 12-05-2022, 04:33 PM
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Thanks - I'll check.

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1984 300D
1972 250
1986 560SL
1991 300CE
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