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  #1  
Old 03-20-2019, 11:12 AM
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Join Date: Feb 2003
Location: Oklahoma
Posts: 1,025
'86 560SL - really hard

I'm having a really hard time getting my SL to start cold. This morning was really tough - a bit damp out and in the low 50s - so not real cold. Took me about 60-90 seconds of cranking and then it fires, very slowly at first. After a few minutes of babying the gas pedal, it will run fine.

Hot starts are fine and once car is warmed it, it runs great! Warm starts ok as well, but starting gets progressively more difficult the colder the motor gets.

I have looked at the cap and rotor and they look very good...

any thoughts?

ryan
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RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE
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  #2  
Old 03-20-2019, 03:51 PM
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Iím going to guess itís an issue with your cold start injector. Does it start easy if you spray something combustible into the air intake?


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Past mb: '73 450sl, '81 280slc stick, '71 250, '72 250c, '70 250c, '79 280sl, '73 450sl, parted: '75 240d stick, '69 280s, '73 450slc, '72 450sl,
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  #3  
Old 03-20-2019, 04:38 PM
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My understanding is the CSV only works when it is pretty cold outside - ambient less than 50F, maybe even lower. It didn't start yesterday and it was 70F here...

I think it's contributing maybe...
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RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE
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  #4  
Old 03-20-2019, 09:56 PM
Daantjie
 
Join Date: Nov 2014
Location: Vancouver, BC, Canada
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Fuel accumulator probably shot.
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  #5  
Old 03-20-2019, 10:12 PM
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Quote:
Originally Posted by rgnprof View Post
My understanding is the CSV only works when it is pretty cold outside - ambient less than 50F, maybe even lower. It didn't start yesterday and it was 70F here...

I think it's contributing maybe...


Incorrect. Maybe C, not F.


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Past mb: '73 450sl, '81 280slc stick, '71 250, '72 250c, '70 250c, '79 280sl, '73 450sl, parted: '75 240d stick, '69 280s, '73 450slc, '72 450sl,
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  #6  
Old 03-21-2019, 01:58 PM
MatthewZ
 
Join Date: Oct 2018
Location: Sydney Australia
Posts: 1
From what I know, the cold start valve is triggered by the temp sensor on it which reads coolant temp, not ambient air temp. So even in summer, your cold start valve will still be triggered to operate on 'cold engine' (first) start-ups.
I know this doesn't solve your issue, but maybe it will lead to a clearer diagnosis. This may involve checking the relay that powers the csv, or other parts as mentioned earlier (accumulator at pump, csv itself, wiring, etc).
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  #7  
Old 03-21-2019, 04:55 PM
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Join Date: Jul 2009
Location: North America
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I see you've come here for help

Your 86 560SL should have a two pole coolant temperature sensor. When the air temp is <50*F the cold start valve should pulse for a second or two. Below freezing it should do it for 6 seconds or so.

With the car cold either at or below 50*F, take out your cold start valve and stick it into a jar. Have a helper crank the vehicle while you watch.

A stream of vaporized gas should come out.

I believe grounding the two prong pin should get a nice long stream of vaporized gas out when starting. Again, have a helper near by to crank while you juggle all of this.

If gas does come out, then I would look at fuel pressures. This thread has some tips for you to try: https://www.benzworld.org/forums/w126-s-se-sec-sel-sd/2752969-how-test-cold-start-valve-electricals.html

https://www.benzworld.org/forums/w126-s-se-sec-sel-sd/1302387-how-cold-start-valve-works-2.html

Apologies, on BW the CSV operates differently on the M117 engines as opposed to my ancient M116
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Quote:
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Going back to the original post: "Can you get the vac to blow instead?" No. Vacuums are low pressure so they by nature "suck" and nature abhors them.
1984 380SL
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  #8  
Old 03-22-2019, 09:52 AM
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Yea, I figure 2 'heads' are better than one...

Here's what I know after some early morning tests - it's currently 42F 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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1984 300D
1972 250
1986 560SL
1991 300CE
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  #9  
Old 03-22-2019, 05:53 PM
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Join Date: Feb 2003
Location: Oklahoma
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Quick update:

Just checked the duty cycle and I'm not sure what's going on here...

With key on engine off - I'm getting 0 duty cycle

With engine idling, I'm getting mixed results. If I use the duty cycle feature on my 2 meters that read DC, I get about 70% (fluctuates around 70 and if I rev to 2500 rpm, I'm getting basically the same thing). BUT, if I test for DC using the voltage approach, I'm only reading approximately 40mv - with BOTH meters...so I don't know what's happening. At 2500 rpm, the voltage reads a pretty stable 5.8 volts...
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RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE
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  #10  
Old 03-23-2019, 02:06 AM
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Rogue T Tolerant
 
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Location: North America
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The duty cycle should be fixed when cold. Once the engine is up to temp you should be able to read it.

There's a coolant temperature sensor on your engine that might have gone bad. I don't have a test procedure for it but it controls the CD start valve and other enrichment related activities. Do a search on that topic. I believe your 86 has two different coolant sensors that achieve this functionality. The links I posted make mention of it.
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