stall during warm up

[hands_aus]

Hi Group,

My early 250SL (auto) has been running great for about 6 months until yesterday. With the help of Joe Alexander we have leaned it out to be within proper exhaust CO % level.

When I start my car, I let it run up to normal working temperature.

Yesterday it started ok but I noticed it was idling a bit slow (around 500 rpm).

As the temperature increased the car stuttered and stalled.

I restarted the car and as long as I had my foot on the accelerator pedal it turned over.

As soon as I removed my foot from the pedal it stalled.

I have done nothing to the car, engine-wise, other than clean the plastic protector cap that covers the distributor and spark plug leads.

(I have rebuilt my old style electric fuel pump and it is going great, but that is another story)

Previously and as part of getting the fuel mixture correct, I took out two shims between the body of the thermostat and the IP.

Today I checked

The INJ PUMP Rack. It is working freely. I put a 5 mm bolt in the end and it moved and returned to the normal position.

The IP air cleaner is clear. I can hear the air being sucked in while the engine is cold.

The INJ PUMP Thermostat seems to be working (maybe too well) because the stalling only happens slowly as the engine warms up.

I suspect that I need to replace the IP Thermostat, but, I think I might try re-inserting the thinner of the two shims that I removed 6 months ago.

Does anybody have any suggestions?

Thanks

Bob (Brisbane,Australia)
early 250 SL, RHD

[Naj ✝︎]

I would start by checking the normal idle air screw. Maybe remove the assembly from the inlet manifold and give it a good clean out.
Were you able to fit the paper air filter element?
naj

'Kloines Scheisserle'
65 230SL
68 280SL

[ja17]

Hello Bob,
Also check and make sure the oil level in the pump has not risen above full. This could change things a bit.
It is not that unusual for some settings to settle in or change after major adjustments have been made. Be cautious not to jump into injection adjustments before the tuning items are checked. Changes in point gap, timing, spark plug condition, fuel supply, fuel pressure and vacuum leaks etc. can also give you these symptoms.
Shim replacement is easy and harmless you can always take it back out. However check tuning also. Good luck.


Joe Alexander
Blacklick, Ohio

[hands_aus]

Hey Naj and Joe,  This is a bit long

Naj,
I have checked the air screw .. it is OK.

No I went off the idea of the paper filter because the interior of the housing is different from the paper filter unit.
The oil bath unit has a shelf built into the case on which sits a steel meshed filter and the lid has a huge steel meshed filter built into it.
I would need to replace the whole unit.
Joe advised me that the paper filter would change the amount of air entering the engine and that would adversely affect the economy. It is bad enough.

Joe,

In the last couple of months I have replaced the vacuum lines to the inlet manifold and brake booster and the injection pump.
The electric fuel pump was rebuilt recently.
The tank to pump fuel hose replaced.
The delivery volume on the Return Line (at the tank end) is about 1.5 litres in 15 seconds.

This morning I re-installed both shims under the inj pump thermostat housing that I removed 6 months ago and it made no difference.

I removed the Coolant Housing with the Thermostat still in it and put it into a saucepan of water and measured the change of the plunger length as the temperature increased.
When the water boiled the Thermostat Plunger had extended by approximately 9-10 mm. I figured it was OK

I then took the Air Valve Housing off the Inj Pump.

I removed the aluminium Air Valve Piston and the Plunger with the spring on it.

There seemed to be little or no lubrication in there and it was dirty and sticking. I cleaned it out with a cotton bud and wiped the exterior over with a cloth soaked in petrol.

The Air Valve Piston was a little scored and so was the wall of the Air Valve Housing.

I then used engine oil to lubricate the Air Valve Piston and Air Valve Housing and spring/ Plunger.

I assembled the Coolant Housing to the Air Valve Housing. I tested the Plunger and it moved freely.

I then added the two shims under the Air Valve Housing and fitted the whole thing to the body of the injection pump.
I added new heater hoses and re-attached the vacuum line.

I topped up the overflow tank and started the car.

It ran smoothly. The engine stalled as the temperature reached 180 F.
At the beginning the engine stalled at 160 F.

I played with the INJ PUMP fuel mixture screw and the manifold air screw  increasing the richness and air until it kept on running while at normal operating temperature.
When I took the car for a test run, it was running a bit slow. The motor was running unevenly.

Tomorrow I will test its air /fuel running mixture.

Joe,  you told me the procedure of removing the top of the control rod to the injection pump and increasing the throttle air etc.
I will be interested to see how the car goes at start up and if it continues to run at normal temperature.

Joe I have some questions

How do I get the Thermostat out of the Coolant Housing? Mine was stuck in there and because after the test I decided that it was working properly, I didn’t remove it.

Will the scoring on the Air Valve Piston and Air Valve Housing be a problem in the future and should I think about buying a new housing or having the existing one rebuilt and maybe a new Air Valve Piston made out of stainless steel?

Will the engine oil (20W50) be sufficient lubrication or should I use high temp grease?

I will keep you informed of my progress

Bob (Brisbane,Australia)
early 250 SL, RHD

[Cees Klumper]

Hello Bob. What a drag - engine running fine and then all of a sudden these problems. Just some thoughts here:
(1) have you checked the fuel flow? Maybe something clogging the fuel supply in the tank, fuel filter or the return lines? - might explain the rough running and stalling when not enough throttle is applied; (2) ignition: when my own engine all of a sudden started acting up last year (running rough WHEN WARM, not when cold) it turned out to be the spark plug leads; (3) is the vacuum advance mechanism working right? Check with a timing light.
From all you have told us over the past year I feel as though I know your car as well as my own. Wish I could help you troubleshoot it with you right there. Anyway, good luck and keep us posted please.

Cees Klumper in Amsterdam
'69 white 280 SL automatic

[ja17]

Hello Bob,
Read your spark plugs after a test drive, they may give you a clue. You may want to check and see if your timing has shifted.
On your other questions, The thermostat in the "warm-up device" is just a friction fit, It should pull out. A little scoring in the housing should cause no problems. A little engine oil is fine for lubricating the mechanism. Good Luck!


Joe Alexander
Blacklick, Ohio

[hands_aus]

Hey Joe and Group,

The motor now continues to run during warm up and as the air valve closes there is no sputter or stutter.

I have taken it for a test drive (only locally and not on the highway yet) and it seems to be idling about the correct speed. (I should buy an electronic tacho and connect it to the coil, just for testing)

Removing the Inj Pump Top linkage Rod and increasing the Throttle Air supply caused the engine speed to increase only marginally before it faltered.
Similarly, increasing the Inj Pump fuel supply, caused the engine speed to increase only marginally before it faltered.

This indicates to me that the air/fuel mixtures are correct.

I will take it for further test drives and check the PLUGS for colour etc. before saying I am completely satisfied.

I am going to add “Lubricate the Inj Pump Air Valve” to my schedule of Regular Maintenance. Maybe do it every 12 months.

Thanks for your help.

Bob (Brisbane,Australia)
early 250 SL, RHD

[n/a]

If it has a solenoid it will be the solenoid. Same problem for any make of car of that era. My Fiat Spider does it occasionally. With fiats you clean out the solenoid (usually full of crap from the fuel lines). Rust is a problem on the SL solenoids and they are very difficult to fix as you have to drill them open to clean but replacements cost $£$£$£€€€.

Cheers
Andrew
London (formerly Melbourne, Australia)

[bayleif]

Group,
Here's a question. Bob describes a procedure for disconnecting the linkage so that you can effectively test the air to fuel mixture by increasing either the air supply or the FI pump fuel supply. This is done at idle. Engine warm?
As I recall the procedure for adjusting the idle, with a warm engine (warm up device fully closed) the idle air adjustment is closed so that the engine is idling about 200 rpm or so less than maximum idle. This would leave the adjustment such that the engine is just slightly rich. So my question, shouldn't the idle have increased more when Bob increased the air supply then it did when he increased the fuel supply. In fact, shouldn't increasing the fuel supply have caused the idle to decrease?

Chuck Bartlett
1969 Signal Red 4 Speed

[ja17]

Hello Chuck,
The increase in rpm should be around 60 before faultering. This is not a rigid specification, just a guideline.


Joe Alexander
Blacklick, Ohio

[hands_aus]

Hey Chuck,
The engine speed did increase more when I adjusted the air supply, than it did when I adjusted the fuel supply.
The additional fuel caused the engine speed to marginally increase before decreasing and almost stalling the engine.

Bob (Brisbane,Australia)
early 250 SL, RHD

[jeffc280sl]

I had a very similar problem with my 1970 280SL.  I adjusted the CO and warm idle with my new gas analyzer.  This effected the cold start idle which dropped to such a low rpm that the car almost stalled.  I oiled the air valve in the warm running device and removed 2 of 4 compensating washers with no change.  Decided to spend $25 and replace the thermostat.  This seems to have been the problem and it may have solved a long standing very intermittent idle problem.  After driving the car a while I would let it sit for and hour or so.  Sometimes after restarting the idle would be very low and then ok once the car got warm.  Time will tell.

Anyway the car now has a cold idle at 1000 rpms.  I need to go back when its warmer outside to reset the CO and warm idle rpm.

Before I forget, the new Behr thermostat was slightly different than the old one.  The base where the plunger extends was brass.  The old one was hard rubber or plastic and slightly cone shaped.  The new brass base was not coned shaped and it would not fit into the guide ring.  Referring to the BBB diagram I noticed the thermostat seated neatly into the guide ring.  I decided to ream out the guide ring so that the new thermostat would seat properly.  A little bead of Waterpump RTV silicon on the top flange of the thermostat created a great no leak mating with the housing and that was it.

Jeff C.
1970 280SL 4-speed

[hands_aus]

Jeff,I have replaced the thermostat too.
I noticed the same thing about the shape. The silicone sealer worked for me too.

After reading of the problems being described on here and the other 113 site I checked the existing points dwell and it was 48 degrees (should be 38 +3 -1). I then checked the gap and it was .003" .......way too small a gap, should be .012" minimum.
I looked at the fibre rubbing block of the points and I decided that it must have worn down (affecting the timing and hence the running). So last Monday I bought new points for my car.
I asked the local Repco shop for a set but their catalogue didn't go back far enough.
I went back with the actual points and found an identical Bosch set for an International Truck at $11.00.
After installing them and adjusting the Dwell angle to 39 Degrees, the car nearly jumped off the floor when I started it.
The idle speed was about 1200 RPM. I wound in the manifold air screw and let it warm up to normal operating temperature. Then I took it for a test drive.

The car has never responded so well as long as I have owned it (18 months). It was quick on take off, the transmission changed smoothly, there was no hesitation, it was like i had the car in first gear all the time at the traffic lights.

I could smell petrol in the exhaust so I adjusted the fuel /air mix until it was correct. Unfortunately no CO meter here, yet. I also kept my eye on the colour of the exhaust pipes.

Last Tuesday I went for a drive to the beach and back. I checked the fuel gauge and it seemed to be moving at the right amount for me to be happy with my adjustment.

The consumption ended up being 16.84MPG which for my car is excellent, given it has been 12mpg.

I will have the CO level checked in a couple of weeks.

Bob (Brisbane,Australia)
early 250 SL, RHD

[n/a]

Bob,
I read this post with great interest.  I had exactly the same symptoms that you describe.  I enrichened the fuel mixture by turning adjusting screw on the IP clockwise a few notches.  Then, I raised the warmed up operating rpm to 900 via the air adjusting screw at the engine air intake.  This solved the stalling problem during pre-warm up.

Can you explain more about how you adjusted your CO% by removing shims?  I tested the CO using a Gunson gas analyzer and I cannot get it lower than about 8%.  The BBB says I should be at about 4%.

Best regards,
Don

[ja17]

Hello Don,
These oval shaped "adjustment shims" with three holes, when removed will lean the injection pump through the entire range of engine rpms. Start by removing a thin one first. Adding shims will richen up the engine fuel mixture. You can always put them back if the adjustment does not work. You should not have to unhook the water lines.

Download Attachment: warn up device exploded.jpg
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The other full range adjustment is a rack adjustment through the access screw.

Joe Alexander
Blacklick, Ohio

[hands_aus]

Hey Don,

I have been off line for a couple of days.

Joe will guide you to see the light.

Bob (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[n/a]

Hello everyone

It appears that cold run problems (as against cold start problems) are pretty common. I have the same experience, especially as the weather gets colder here in Sydney. My 230SL starts easily when cold and runs fine for about two or three minutes but then starts to stall as soon as I stop at a set of lights. This happens for about 10 minutes before the motor is properly warmed up. By the way Bob, what is the Repco part number for those points? It's good to know that there is an alternative.

Thanks
Mark

1965 230 SL light blue, auto, RHD

[hands_aus]

Hey MarkR,

My early 250 sl has an "051" cast iron distributor.
This might be different from your 230 SL.
The points were a Bosch set, number GB 527.
Note: I had to modify the cable lug but the physical set of points were identical.
I think the MB points have an exact cable lug, MB part no. 1237 013 027

I think the stalling problem is centered around the air slide valve not moving easily. It might need to be oiled and maybe freed up.

My car gave a huge cough last Tuesday when I drove it before letting it warm up fully. Like your car, once mine was at proper operating temperature I had no further problems.

It is almost 12 months since I last oiled that air slide valve. So shortly I will be giving it a squirt of oil.

Bob (Brisbane,Australia)
RHD,1967 early 250 SL, auto