Cold start valve solenoid

[gordon]

Hi, 1965 230 sl rhd,  can't start from cold( it was ok before)  I've checked that the incoming fuel filter is clear, I've lapped in the spring loaded valve so it no longer leaks so I'm at the solenoid now. When I crank it over I get a reading of 0.005 v for sometimes about 3 seconds and other times for as long as I try to start it.  With the solenoid free from the inlet there is no movement of the pin which should let fuel through. Is the voltage to the solenoid enough to activate it and can I give it 12 v direct to check it's working?

Also does the double inlet manifold jet unscrew from its housing?, I'd like to check it's clear and if not to sort it.

Thanks Gordon

[roymil]

Hi Gordon,
I had similar behavior with my early 280SL.   I've found the fuse for the CSV solenoid blown before, so of course check that first.   Many DC voltmeters wont respond very quickly to the short voltage pulse from the thermo-time switch, so you might miss the event, especially if its warmer and the pulse is shorter (by design).  It wont pulse at all on a warm engine.   You might try hooking up a 12V test light to the solenoid (12v test light from any auto parts store should work).  Place it so you can see it from the driver's seat when you turn the key.   It should flash on for a short time as soon as you start cranking cold.   

When I was first bringing up my engine from its 25yr slumber, I actually hooked up a 12V LED to my solenoid semi-permanently so I could always see for sure it gets voltage. On a cold engine I'll see it come on during the initial cranking for about a second, just long enough to notice, although it should stay on longer if colder.    When troubleshooting I have also briefly brushed the solenoid input terminal with a 12V hot lead just to hear the audible click and know it was actuating.   ***!!!BEWARE!!!*** Be careful doing that with an unfused lead though, and certainly don't do it unless you are absolutely positive there are no fuel leaks anywhere around the CSV or the intake manifold.   There will be a spark if you touch that solenoid with a hot lead.   That wont end well if you have any fuel vapor around.   Have a halon fire extinguisher around if you try this.  Good luck!

[gordon]

Thanks for your response Mark. I note your safety concern re fuel vapour. I was concerned about giving the solenoid 12 volts and perhaps trying it! I'll momentarily power it from the battery  away from the fuel.

My other query was asking if the twin jet  which squirts into the manifold can be  removed from the mounting point so i can check if the jets are clear.

Thanks Gordon

[roymil]

I don't remember having to remove the twin jets.  I think I just soaked that whole assembly overnight in parts cleaner and then blew them out with compressed air to be sure they weren't obstructed.

[gordon]

The solenoid works fine with direct current from the battery, however with a test  light connected to the solenoid wires instead of the solenoid no light!.
I'm now looking at a relay (4 pins) on the inner wing\fender near the battery. Am I heading in the right direction?

[roymil]

It certainly could be the relay, or bad wiring/fuse.   It could also be an issue with the thermal time switch which triggers the relay based on temperature.  I found this post from just a year ago with really good discussion by some of our most experienced members on how that switch works.  Get out your schematic!  -Mark

https://www.sl113.org/forums/index.php?topic=30453.msg220698#msg220698

[roymil]

also, don't forget to re-read the tech manual starting aid tour : https://www.sl113.org/wiki/Restricted/Engine-starting-aid-tour
I learn something new every time.  Many thanks to those before us who put all that together!  -Mark

[gordon]

I reread the tech manual as suggested and it seems that the TTS is bad so I have bypassed it and now have a working cold start valve solenoid. Although I have fuel on the solenoid side of the spring loaded inlet valve non squits out of the inlet manifold jets so they must be blocked. Do the jets unscrew or are they pressed in?
Thanks Gordon

[Cees Klumper]

I recall a recent thread where the question how the nozzle is fixed into the aluminum housing was also raised, and I believe the answer was it is pressed in. I think Benz Dr advised to gently twist/pry it out, but best search for that thread ('restoring a CSV' or somethimg along those lines).

[gordon]

There is a reference in the technical guide to using acid to clear the jets but that must must have been done from  the non jet side because the jet orifices are so small.
I'll resist the temptation to pull the jets till I learn more

[roymil]

I'd avoid acids that might etch the metal and stick to carb cleaner (or maybe acetone) to dissolve what is probably fuel varnish/residue clogging the jets.   Might also be worth checking and changing your fuel filters too in case some contaminant made it through to clock the jet. 

[gordon]

Benz Dr confirms that the jets are pressed in and can be gently eased out having marked the orientation of the jets. Care needs to be taken to make sure that the jet is refitted securely, a dislodged jet could cause a lot of damage.