Engine Doesn't Start When Hot

[98telecaster]

Hello.  I am new to this group.  I have a '66 230 SL that has been in my family since it came off the line in 1966.  I am not as familiar with automotive repairs as my dad and granddad were, but consider myself handy and would like to learn more about the car rather than take it to the one guy in town who works on this class of vehicle. 

I just had some work done to the engine.  Head gasket was busted.  So the entire engine was taken apart to inspect if any other problems were present. 

My 66 starts up after sitting for a month or two in an instant.  No issues aside from needed to give it a few pumps as to not shut off since it's cold.  I can drive it just fine.  Recently, when I drive it for about 10 minutes to get to the gas station, I pump the gas, and then try to start it up and it won't start.  It's not the battery.  The engine is warm.  So I did some research. 

It looks like there are two starter valves:  a cold start valve (CSV) and, I guess, the not-cold-start-valve (I'm learning, be nice!).  Because the engine starts up just fine when the car's been sitting, but doesn't start well at all when it's warm, I'm thinking the cold start valve works ok and the other doesn't. 

I also read the solenoid could have been installed incorrectly.  Not claiming the guys don't do quality work, but on one of the threads I read somewhere that with modern tools the parts could have been over-tightened, possibly.  But hey, maybe it's just an old part that needs replacement. 

I am looking for any advice, vocabulary to engine parts, and helpful information to pull me away from being so dependent on an auto shop.  Not that I want to perform all repairs myself, but would like to be more informed. 

THANK YOU IN ADVANCE!

[Pawel66]

Hi! I think you are starting a great adventure with your car!

I am not a mechanic. I write about your issue as I went through it myself. Twice, actually. And I am basing what I write on a thorough study of the related threads on this forum.

There are a lot of threads on this forum about hot start issues. Type "hot start issue" - exactly like I wrote and you will see many results.

As for the starting aid, primarily cold - there are, I think 3 systems, older and newer on our cars. In essence it is about a temperature feeling device sending a signa to activate a Cold Start Valve on the intake manifold to inject additional portion of fuel for certain time and in certain engine temperature conditions. The same set of devicces is responsible for some injection during warm start, but it may not work during the warm start. My impression is Mercedes have never solved this issue really...

The details of these systems are described in the Technical Manual, in the sectin for Full Members. You may consider becoaming a Full Member - it is not a huge investment, it pays off very, very quickly.

Your system seems to be working perfect when cold.You can briefly check the influence of operation of the cold start system on your hot start by manually providing power to Cold Start Valve while cranking hot engine. Just for e second or two.

Reading through the threads on hot start issue, you may conclude that most or a lot of these issues are related to fuel supply. Engine is in the very lean condition at this moment. Fuel supply need to work perfectly (this short injection of fuel through CSD helps there).

If you briefly check electric side by seeing you have a strong sparks on all cylinders, you may look at the fuel side. Probably the first test is to undo your return fuel hose where it gets to fuel tank, put it in the empty fuel canister, switch on ignition (and fuel pump) and see if you are getting 0.8 - 1.0l of gas pouring within 15 seconds. If you get below - you need to check where the fuel system is clogged:
- fuel filter in the tank (if you say you poured gas in the gas station and you could not start, I am excluding the inner gas tank fuel passages)
- additional (not original) fuel filter you may have between tank and fuel pump
- filter in the inlet of the fuel pump
- fuel pump itself
- fuel line
- main fuel filter
- return fuel line

You just check/clean piece by piece.

Observe safety rules when working with fuel.

If you blow air to the return line to hear it bubbling inside the fuel tank and/or to clean it - cover the opening on your side through which you blow air so that it does not flush back at you in cae the line is clogged.

In my case the hot start issue was caused by:
1. Clogged filter between fuel tank and fuel pump (non original filter that, I think, we need)
2. squeezed fuel line (becauise of my stupidity)

I am sure others will chime in with their advise - probably better than mine.

I think, however, the most time and money efficient way is to go systematically through the components rather than shooting from the hip.

[ja17]

There are four starting versions on the W113 cars. version 2, 3, 4, 5. Version 1 was never used on W113 cars, just old sedans, cabs etc.  All are similar but all are different also. With a 230SL you may have version 2, or 3. Most likely is you have version 3. The two starting devices on your engine are the (CSV) cold start valve on the intake manifold. The name of this valve is incorrect since it is also used for hot starting. The other device is the injection pump solenoid (enrichening device) With two injection pump solenoids, the top one is the starting solenoid. You need a 12 volt test light or volt meter to check your system. Assuming your system is version three, test both devices for function. Activating the starter switch also activates the two starting devices via their electrical solenoids. With version 3, both starting devices function at all starts. Above 95 degrees F (coolant temp) both devices should operate one second only. Lower than 95 degrees F (coolant temperature) the activation increases as the temperature of the coolant decreases. During very cold starts the devices may activate up to 17 seconds of cranking! Once the engine catches and the key is released the starter disengages and all starting devices go off. From this point the WRD (warm running device) (warm-up-regulator) takes over to act like a automatic choke did in old carbureted engines. The WRD supplies extra fuel and air needed for a cold running engine.

My first guess for your problem is that one or both starting devices are not being activated for one second during hot starts. You'll need to confirm this for us so we can move forward with the fix, or move onto a different cause.

[UJJ]

It is always a pleasure to read Joe Alexander's responses to our various questions. So much knowledge, so great advises and help!
He really is a treasure to our forum.
Even though I personally did not need to seek for his advise, but learning more and more about our cars just reading his posts.
Thank you so much Joe,
Urban

[ja17]

Thanks Urban, you are too kind.

[mauro12]

Hi guys , sorry it’s been 2 years since you opened this topic but I wanted to expose to you my experience.
My 250sl is equipped with the r22 injection pump with no solenoids. I have no difficulties with hot starting but during very cold starts It helps to press half way the gas pedal .
Maybe this condition depends on the r22 pump ? What is the benefit of an injection pump with no solenoids ? There should be a reason why this pumps can provide good starting without having solenoids .

[mauro12]

In other words , why the later injection pumps were equipped with 1 or no solenoids ? Is there a benefit for having no solenoids in the injection pump ?

[Pawel66]

Mauro, I think the reasons of eliminating solenoids may be cost and simplicity.

If I am not mistaken, one of the solenoids was a shut-off solenoid, required in the US for emissions control and the other one was to support cold start. Its elimination was, I think, with the evolution of cold start systems.

I would probably look for reasons for difficult cold start in overall engine tune-up and in operation of the cold start system (TTS, relay, CSV).

I am not sure, but pressing the gas pedal may be quite common also for the cold start.

[Shvegel]

Mauro12,  The reason for the elimination of the enrichment solenoid is on your later pump they improved the design of the delivery valves (check valves at the outlet) of your injection pump.  The old design tended to leak fuel back into the pump which caused vapor lock and particularly hard starting when warm.  The new design starting from R22 on up used a ball valve rather than a pintle valve and was much less susceptible to leakage.   Once they solved the issue with the delivery valves there was no more need for the enrichment solenoid.

As an aside I am fairly certain the R22 pump was never installed on the 250 from the factory.  It should have an R18.  Your pump may have been tuned down to r18 spec to keep it from over fueling the engine.  Regardless it has the newer delivery valve design and if it has run for a while like that it is probably OK.

[mauro12]

Thank you for the explanation. Yes my car was equipped with the r22 pump from the previous owner . I don’t know the reason . Probably the original pump was worn out .
By the way ,in September I’m going to have my injection pump overhauled by oldtimer Technick in Germany . He told me that he will replace the space cam of my r22 with the space cam of an r18 pump , using the 3D printing technology and calibrate my r22 with the specifics of the r18 .
Even if it’s not the original pump , I will have the benefit of a more modern pump compared to the r18.