starting problems

[Tony T]

I have a 1967 250sl that I have a recurring problem with.  The car will always start when the engine is cold.  I can drive it for a long period of time or a short period of time.  Either way once I shut it off I have to wait for at least 30 min. before it will start again.  The engine will turn fine but it wont fire up.  I have drained the entire fuel tank replaced the filter in the tank, change the fuel filter in the engine compartment but I still have the same problem.  Any and all help would be appreciated.

Tony T

[Cees Klumper]

The car seems like it needs the cold start help. I know some have hard-wired a momentary push switch inside the cabin to activate the CSV (Cold Start Valve) to give it the extra squirt of gas when cranking. You might try this as a 'fix'. If you shut the car off after say 30 seconds of starting up from cold, does it start then? Probably does.

[franjo_66]

Tony, as far as I know a lot of the 230SLs have a known issue with hot/warm starts due to leak down of fuel via the valves on injection pump. I had this same issue even after getting the injector pump overhauled, CSV rebuilt and the injectors cleaned. On top of that I installed a new 123 electronic distributor, new coil, new wires and so on. Cold starts are fine but hot starts were a pain.

Simple solution (even recommended in the BBB) is to depress the accelerator when you do a hot start. I do this and the engine catches straight away. No fiddling or having to install customised set up.

The design is improved in the 280SLs (not sure if this includes the later 250SLs) and most 280SL owners that I know have no problems with their hot starts.

Regards
Franjo

[w113dude]

It could be a weak fuel pump (heats up) have you checked the pressure?

[wwheeler]

For hot start problems, there is also this factory fix. It activates the cold start valve on the intake even when the engine is warm. Sounds like might be a fix for Tony's problem. Does the same thing that Cees is talking about but is automatic.

[ctaylor738]

The parts for the factory fix have been NLA for a long time.

Here is my solution with a timer relay:

http://www.sl113.org/forums/index.php?topic=17329.0

And here is a schematic for the new relay.

[wwheeler]

I bought the kit (#001 545 16 24) from the Classic Center no more than two years ago. I haven't installed it yet, but I am sure it came with everything for the modification. Might give the Classic Center a buzz and see.

[ja17]

Tony, a lot of things can cause starting problems.
Ignition contact points set too close can cause starting problems especially on hot engines. Faulty ignition coils can get lazy as they heat up. These items are easily checked. Check for ignition spark when you are having hot starting issues (hold the center distributor wire close to ground and watch for spark as engine is cranked)

You will need to make sure that the basics are in order first. The main fuel filter should be clean.  Your fuel pressure should be up to specs. Low fuel pressure could be caused by fuel line restrictions, plugged fuel screens in the electric fuel pump or fuel tank and defective check valve  on the fuel return line. Vapor locking fuel in the system can happen on hot engines if the fuel return line is restricted or the pump check is blocked. A lean running fuel mixture will also aggravate warm starting problems.  A split linkage test on your warm engine will confirm this.

Your engine starting aids should be checked next. Un-hook the metal fuel line going to the cold starting valve on the intake manifold. Remove the metal fitting screwed into the intake. Check to make sure that the fine screen in it is not clogged. Also check the the slide valve moves freely.  Re-assemble.

There are several versions of starting aids on the W113 cars. Your 250SL should be version 4.  On cold starts (below 95F) the intake CSV (cold start valve) will activate. The injection pump enrichment solenoid will also activate on cold starts and hot starts. Check these two devices with a 12 volt test light to make sure they both work on cold starts. Next check the injection pump enrichment solenoid to make sure it starts when the engine is hot. ! (this could likely be your issue).

If one or more of your starting devices are not operating correctly get back with us and we will help you pinpoint the problem (sensor, relay etc.)

Most likely you will find your problem among the above possibilities and modifications will not be needed.

Joe Alexander (ja17)
Blacklick, Ohio