Stalling after engine warms up - Occasionally

[Benz280]

Trying to diagnose a new issue. Over the past few weeks, when doing a cold start idles at around 500 RPM, when engine warms up jumps into normal range 1000.
On occasion, when you stop at a light engine will stall ( will crank and crank as if no fuel or electric ), I wait 20 minuets and it starts ( Putters then runs normally )
Question to the Dr. in the house :
Cold Start Valves ?
Fuel Pump ?
Fuel Tank not vented properly - After Driving I remove gas cap - Poof of air come out.
Any and all suggestions welcomed 
 
   

[roymil]

I've seen similar behavior and have worked through debugging and rebuilding all of the cold start systems at one point or another.  The all interact so several things could be going on but it's suspicious that you mention normal for your car is 1000 rpm hot.   It should be closer to 750, so I think that might be a clue.  Assuming it was once perfectly tuned and adjusted for 750RPM hot, then something changed.  Also, 500rpm is a bit low for a cold engine if all the starting aids are working properly.  I'm an engineer, not a mechanic, but overall it kind of sounds like its too rich. A leaky cold start valve might explain that and thats not uncommon.   The fact it jumps up to 1000 RPM when warmed makes me think the injection pump is getting the fuel flow it needs, especially if everything works well at higher RPM.  If so, I think that rules out the fuel tank, electric pump, venting, etc.  Mine will build some pressure in the tank after driving and warm too and i think my vents are OK.

some questions:
Does it accelerate and perform well when hot and at higher RPM and load?
Are plugs black?
Is exhaust dark when at cold idle and then cleans up?
It fuel milage normal for your car compared to the past?   (I'm not exactly sure what the normal milage is)

The pros on this site may know exactly what is going on just from your symptoms but it's hard to be sure without more info.   Suggest reviewing the WRD page in the manual. https://www.sl113.org/wiki/Engine/WarmRunningDevice

Also suggest looking through the Engine starting aid tour to eliminating suspects. 
https://www.sl113.org/wiki/Restricted/Engine-starting-aid-tour

[Benz280]

Thanks Mark for your thorough ideas as to what could be going on .
Upon rechecking, my RPM at start is about 650, once warm it runs up at 1000. Car starts immediately, in fact I find it amazing how fast it starts even after sitting for awhile.
No smoke at all, plugs are clean.
Run runs great under load, pull strong . Honestly, haven't done a MPG , too much enjoyment to be concerned with MPG. I will do the math on my next long haul.
I'm wondering if the problem could be with the Injection pump thermostat.
The cold start solenoid has been disconnected ever since I purchased the car, given that I do not dive in cold temperatures, don't think this comes into play, am I wrong ? 

Again, its an intermittent thing, but always seem to make it home

[Benz280]

Forgot to mention, did look at the WRD and seems to be working properly, did the hot water test.

[roymil]

Sounds like a pretty well running car overall with just some infrequent idle & starting issues, so thats really good.  It took me a long time to tune for reliable starts where my plugs stay perfect and there's never smoke.  I was going to ask about WRD but see you checked that.   I have my cold start solenoid at the back of the injection pump  disconnected too, as I think many of us do, especially in warmer climates, although it might still help you on very cold days in NJ, but thats not your problem here. 

So, yes, maybe another thing to check is the thermo-time-switch.  I wonder if the hot-start problem is really a warm-start problem?  ...only happens if the engine is partially warmed but still below the temperature (~35C) that the switch is designed to stop triggering the CSV, and then maybe it is still pushing a small bit of raw fuel into the intake and making it too rich to start easily (ie, flooded) which could explain why you come back in 20 minutes and it starts right up, although it would be cooler then too and the WRD would also be in a different place, so hard to know for sure.   Multiple things are going on but I have heard from at least 2 sources who have put a manual cut-out switch in their CSV circuit to be able to force it off and prevent warm start flooding problems, so clearly that is a real "thing", although I haven't experienced it myself.   Given that is a thermo mechanical switch that heats a physical element up to close the ground for a certain time vs. temperature, it's easy to imagine it being out of calibration, especially if it's original.  Fortunately that is something you can bench test with warm water and a thermometer just like you did with the WRD.

So combine that with hot and cold idle RPMs not perfectly in spec and you might have a situation where under certain edge cases you have issues.  If it were me, remember I'm not a mechanic, since its a pain to pull the thermo-time switch out, I'd first go carefully through the idle tuning guide on this site and try to get the cold and hot idles a little closer to spec, but don't make huge changes since you have an overall well running engine.   Just getting the hot idle down to ~750 RPM may buy you the mixture margin you need.   Also in going through the very systematic idle tuning process you may figure out why your cold idle is low and that could help too.

The only other thing I can think of to check is timing, but it sounds like its in a happy place with good cold starts and good power so dont want to fix something thats not broke.

Thats it, I'm out of ideas, maybe some other vets on the site will chime in.   Good luck !  and hey, if the pagoda continues to give you the cold shoulder just go fire up the shelby ;-)

[kampala]

The gasp and poof of air you notice when opening the fuel cap is typically due to your fuel expansion tank not being able to breathe — blocked vent lines.

Several folks have had the same issue.  I used a solid copper wire and fed it through the small vent lines and that opened them up.  Others have used a piano string and carb/brake cleaner.  Once these vent lines are cleared, the tank can breathe via the expansion tank. 

You can access these vent lines from the trunk by removing the fuel hump cover next to the spare tire.  You should push wire into tank and towards expansion tank but clogging is typically within tank. 

This link may help:
https://www.sl113.org/forums/index.php?topic=32821.msg239947#msg239947

[Iconic]

Benz280,
Your issues sounds like mine on my first Pagoda back in 2009.
It would run nicely and shut off after about 20 minutes (while driving or at a light, it didn't matter).
Basic advice would recommend you should have the car in good "tune" with known good components, and do the linkage tour to insure your setting are correct .......
But, if I were you I would skip to the chase. Your car runs, so you have spark, fuel, and compression, but, not all the time.
Another requirement is to have 1 liter per minute flow from your fuel pump after all of the connections and hoses. My understanding is that this keeps the FIP (Fuel Injection Pump) cool, otherwise it can vapor lock??? After my car "stalled" it would take 20 minutes or so to "cool down" (20 minutes, just like yours) so that it would re-start and run normal for about 20 minutes, then shut off.
So, I would disconnect the fuel line that feeds back into the fuel tank, and measure the flow at that point. Mine was less than 1/4 liter per minute. If you have a blockage, you will need to work upstream to find your clog. FUEL IS DANGEROUS. If you are not experienced, you should have a mechanic do the test.
For me, it was that return line to fuel tank. I cleaned it out and drove the car successfully for about 9 years.
Many on this forum have seen the car. I'm just stating it drove great and I was able to go to Ohio and many other places with it. On a 50 year old car, sediment can start to clog lines, especially if the car sat for any significant lengths of time.
Whether this solves your main issue or not, it is still a great idea to make sure your CSV and/or WRD are not dumping fuel into the engine as this will wash your cylinder walls which will ultimately ruin the finish on those walls.
Good luck to you and keep us posted.
Mark

[Benz280]

Thanks everyone for your input on this, one of the additional pleasures of owning a 133 is the investigation side of identifying issues .
Looking to identify where each of these lines go and how they function . 
Yellow
Green
Beige
Red
Blue