cold start stalling

[Mqueretin]

Hi there,

the 250 SL will start easily when cold, however the engine will run very roughly until it starts warming up. if i'm not continuously pressing the accelerator, it will stall (but start again easily). When the engine's temperature is starting to increase after a few minutes, then it will keep idle without stalling. When at normal operating temperature, the engine runs very nicely and smoothly.

On the car, the ignition was changed, timing is OK, plugs are new, the heat sensor on the fuel pump was changed recently, and so was the thermostat in front of the cylinder head. Any idea of what I should be checking next ?

Many thanks for your suggestions,

Marc

Marc

250 sl 1967
2 cv citroën 1983

[Jonny B]

Take a read of Pagoda Notes Vol 8 no 1. There is an in-depth discussion of the injection pump and the type of check valves in the pump. Richard Simonds put together a nice write up of what he did to fix his car.

[ja17]

  Be sure your engine linkages are correct first.  Observe that  the WRD cold air supply shuts off when the engine is fully warmed. Use the "split linkage test to determine if the engine is running rich during warm-up.  If so you can removes some oval shims under the WRD to lean out the cold running mixture. Keep us up to date! Ask questions as needed.

[Mqueretin]

Hi again and happy new year to all.

It's a long time since i asked the question as I had little time for progress, but could spend some time on the 250 SL during the Christmas break. As a reminder the engine starts relatively easily, but very roughly until warn and will stall unless the level of rpm is kept at 1500+ It takes around 4-5 minutes to be stable and will the  run very smoothly and very nicely once at normal running temperature.

I focused on the CSV and did a number of tests. The CSV seems to be working fine: the solenoid is working (I tested it on a battery), fuel is getting into the CSV, which does not seem to be leaking. It sprays OK and the relay is working (a test lamp lights up for a couple of seconds when cranking).

I'd like to test the relay of the injection pump thermo-switch but i don't know how to do it: i could see no wire connected to the thermo switch itself, so  I connected a wire of my test lamp on the solenoid at the rear of the pump and grounded the other but no light showed when the engine cranked/run: could any one let me know how to do it ? (The thermo switch was replaced back in 2013, so i doubt that there would be any issue with that, but i want to close doors).

the thermo-time switch near the ventilator is also new from 2013.


If CSV is ok and if both thermo switches (injection and time switch) are new  and operating normally, what else would you suggest I check next ?

Many thanks.

Marc

250 Sl 1967
2CV citroën 1983
SL 300 2010

[Jordan]

Marc, did you check your linkages as Joe suggested, as well as confirming your WRD is functioning correctly?  There is a lot written up on the linkages and WRD.  The WRD is notorious for sticking if the car sat for any length of time and they are very easy to check if working correctly.  Just remove the air filter from the side of the WRD.  Start the car cold and put your finger over the hole where the filter was removed.  It should be sucking air, enough to pull on your finger.  As the car heats up the air flow should slowly decrease until it stops when your car is fully warmed up.  If this the case then you know your WRD is working.

[Mqueretin]

Hi Marcus

Thanks for the comment. Yes I did check the linkage and (unfortunately) this is not the issue.  I will look at the WRD.

Looking at the notes on this site, i saw that if a test lamp connected to the CSV is glowing for 1-2 seconds only (which I experienced) when cranking,  then the TTS might be bad. I will test that too.

The Haynes manual also suggest checking if the control rack rod on the injection pump moves easily. is it something that can be done with the pump installed ?

Since I don't recall my car running cold easily, should the idle RPM level be the same as that of normal running temperature or should it be higher ?

Cheers,

Marc.

[Benz Dr.]

It's not your CSV and is more likely the WRD. If it runs better when warm, that's a very good clue you should be following.

[Mqueretin]

Thanks Dr Benz,

I think you're right:  the test light does not work during and after cranking when connected to the solenoid at the back ed of the injection pump, so the relay may be 'kaput'. I'll test also the air filter as suggested below. On the car, the device on top of the injection pump is new from 2013, but the relay was not changed.

Best,

Marc.

[Mqueretin]

I tested again: test light on fuel pump solenoid only works when grounded directly on the battery, not on other parts (e.g. engine valve cover or body) which I find rather strange as I had no issue of grounding when I grounded for testing the CSV. Test light then only works when the engine is cranked.

I could not check the air being sucked in the air filter as the engine will stall by the time I get out of the car and there was no one available to assist.

Cheers, Marc.

[Jordan]

Marc, just so we are talking about the same air filter, here is a pic of the air filter on the WRD.  You will need a thin wrench to get it off.

[Tyler S]

Steer clear of the solenoids and CSV for now. They are starting aids only. As Benz Dr mentioned, focus on the WRD (warm running device). This is what enriches the fuel mixture during warmup until the engine is at operating temp. Your symptoms point to this. The small thermostat inside could be bad and stuck in the extended position, as well as the sliding valve being stuck.

[Mqueretin]

Thanks al for a very useful input. I have not yet solved the problem, but I know what to look at. 

yes that's the filter i was looking at but i couldn't test it on my own as the engine would stall before i could reach to it. As the car is in a holiday house and i won't be back there before a few weeks, i'll update then.

cheers,

Marc.