warm running problem

[enochbell]

OK, so I have had this problem for several years and I now have the time to finally fix it.  I have been to the technical wiki, I have searched and researched, and I am still stumped, so I am here for some advice.

My '64 230sl starts fine, in cold weather or hot.  It runs fine for about 10 minutes, then gets rough below about 2k rpms.  Above 2k it is smooth and powerful, below 2k it stumbles and sputters.  Idle is rough but driveable.  The car will behave like this no matter how far/long I drive it, regardless of ambient temperature and regardless of city/highway/combined route. 

However...

If I shut the car off and let it sit, and it must sit for at least 10 minutes, it returns to it's normal happy self and I can start it and drive it for the rest of trip with no issues. The stumble disappears and the idle is fine.  The key here is that the car must be off for at least 10 minutes.  Anything less and it will restart but I will have the bad idle and stumble/sputter below 2k.

I know that sounds screwy, but there it is.

Any advice would be really appreciated.

Best,
g

[ja17]

Is your main  fuel filter is clean?  Check the ignition point gap and dwell. Sounds like a fuel issue, but don't rule out ignition issues for an unusual problem like yours. Try loosening the gas cap in case you are getting a vacuum build up in the fuel tank.
Keep us up to date.

[enochbell]

Thanks Joe, I appreciate your thoughts.  I have gone through the items you suggested, the fuel filter is new, I have electronic ignition, the car runs great after I give it the 10 minute rest after it warms up.  I know this sounds odd, by my thought is that there is something that is causing the fuel delivery to stay rich until I stop the engine and let it cool a bit.  Once I do that, it will run perfectly.  Until I do that, it runs like crap.  Is there a way to manually disconnect the relay that keeps the fuel delivery in "rich" mode?

Thanks again,
g

[114015]

 

WRD (warm running device) on the fuel injection pump?
Is that one working correctly?

Sorry, I am not an expert here. Joe and Dan are.

Good luck!
Achim

[jacovdw]

...Is there a way to manually disconnect the relay that keeps the fuel delivery in "rich" mode?

Hello Greg,

If your FIP has the solenoid on the back that richens the mixture temporarily during the starting process, you could just disconnect the wires and see what happens.

Have you checked the function of the individual components of the cold start system?

Another possibility, as Achim has mentioned, is to check the WRD for freedom of movement of the slide.

Does the thermostat housing of the WRD get warm?
What happens to the airflow through the WRD air filter during the warm up phase?
Is there a difference in air flow before and after the 10 minute pause?

CSV not leaking?

These are just a few questions I'm toying with when thinking about your situation.

[ja17]

Hello Greg,

You may want to hook a fuel pressure gauge to the metal fuel  line at the intake manifold CSV and actually watch to see if the fuel pressure changes during these episodes.

[enochbell]

Thanks all for the help.  I tried disconnecting the leads to the solenoid on the back of the pump.  The car started, albeit with more difficulty.  But the problem remains: the car began to stumble after it warmed up and the problem disappeared when I parked and let the car sit for 10 minutes (all with the solenoid disconnected). So I believe the solenoid and whatever instructions it is getting from the WRD are working correctly.  Next I will take WRD and hope there is something making it stick.  But for the life of me I can't figure out why the problem goes away just by letting the car sit. 

Best,
g