230 SL hot start problem

[gordon]

230 SL starts first time every time from cold but won't start from hot. When cranking over it smells of fuel. I've read dozens of posts but haven't solved the problem.  Timing is set correctly,  Fuel pump delivers 1 litre in 15 seconds to just before the injection pump, 0.85 litre comes out of the pump before the return line and same amount just before the tank in 15 seconds.
The tts didn't send a ground to the csv so I connected a ground to the tts and the cold start valve delivers and doesn't leak.
When hot starting I disconnect the ground to the ccv to avoid flooding although I think that this is what is happening.
The suction at the air filter at the injection pump reduces to zero during warm up.
Linkages set as per book, split link test done

I'm therefore looking for inspiration in solving the problem as I don't want to leave home Incase I can't restart

[Charles 230SL]

Having gone through this same problem with my 230SL, I suspect the check valves in your FIP are leaking down. If you've got an R11 pump with the original cone-valves they (the cone-valves) may be leaking down enough to make hot-starts difficult. Once it does eventually start, if one or more of the cylinders are stumbling till the corresponding fuel line pumps up, its a good indication the cone-valves are leaking: https://www.sl113.org/forums/index.php?topic=34691.msg254035#msg254035

[UJJ]

If the check valves are leaking, wouldn't that be more of a cold start problem?

[gordon]

Thanks for your input.

Mine is fitted with the R11 pump.   I don't think I've ever been able to start it hot (or warm) to determine if it stumbles on start up.I had the injectors tested before I fitted them and they were said to be ok. Pump I believe has been rebuilt in the past but sat for 5 years before I refitted it.

The fact that this was originally an automatic car and is now manual could I have overlooked something relevant to the hot start problem?

[Charles 230SL]

If the check valves are leaking, wouldn't that be more of a cold start problem?

Leaking check valves are typically evident by difficult hot-starts. During cold starts a correctly operating/spraying cold start valve will normally spray enough fuel into the intake manifold to overcome leak-down in the fuel lines between the FIP and the injectors. My car (and Gordon's) started easily when cold but when hot it was difficult to start. When it finally did start, several cylinders would "stumble" until their corresponding fuel line pumped up enough to open the injector.

Gordon, if all 6 injectors tested good and your CSV is working properly, you may want to consider replacing your R11 cone-valves with ball-valves from a newer pump. The only other alternative I'm aware of would be to hot-wire your CSV such that you're able to manually spray fuel into the manifold during hot-starts.
 

[ctaylor738]

You should have a small round black relay mounted with the cold start relay.  This activates the cold start valve for approximately one second with the engine hot or cold.  Sounds like it may have perished. Test with a hot engine by disconnecting the wire at the cold start valve.  While an assistant cranks the engine, touch a jumper from battery positive to the cold start valve.  If the engine starts, then the little relay is the problem.  SL Tech is selling a replacement regular-style relay with the hot start circuitry built-in.

You might also check if the solenoid on the rear of the pump that moves the rack to full enrichment when the starter is cranked, is working. You can test this by having an assistant crank the starter while you put your hand on the solenoid.  You should feel something between a click and a clunk when the starter first engages.

Good luck,

CT

[Bshaunessy]

To elaborate on what CTAYLOR said ( I just went through this with my 1970 280 SL…..cold start valve wasn’t working and mixture control solenoid on fuel injection pump not working……both easily fixed and now she starts and runs like new!)
(1) first: go to TECH MANUAL/ Wngine Starting Aid Tour….invaluable trouble shooting advice here.  Go through all the steps and you will find your issue.
(2) after I solved the cold start issue : complicated because it involve the Thermo Time Switch ( good. Testing advice in th TM thread)as well as cold start relay ,  as well as the actual cold start valve which injects fuel into the intake manifold on cold( <15c) start.  After going through the testing: TTS resistance and voltage at the "G" terminal, with TTS amounted in manifold; bench testing CSV relay , and finally removing CSV and testing for fuel spray ( when electrically connected): voila! CSV sprays fuel for 2-3 seconds ( and car starts).
Yours , however, is a hot start problem ( also had same)….read on…
(3) DEBUG the "mixture control circuit". Again….good write up in TM thread.  A similar relay to CSV relay controls a solenoid on back of fuel injection pump and momentarily adjusts air/fuel ratio for starting…..does this when engine cold and I believe when engine HOT.  In my case, CSV was working ok but had a faulty wire connection (#86 on the mixture control relay plug).  Easily fixed and now , when cranking, you can feel solenoid on FInpump engage, modulating fuel , just during cranking..

Car now starts reliably… old or hot.
Hope that helps.

[gordon]

Thanks for all helpfull comments. Yesterday I had a conversation with Fred at Tower Bridge Diesels who only deal with our injection pumps.Having been satisfied that there was enough fuel he suggested disconnecting one wire off the solonoid on the back of the injection pump to see what effect it had.

It now immediately starts when hot. Does this mean that the current mixture is already rich and therefore doesn't need the boost from the solonoid? Cold start is still fine ( it still gets a fuel boost when hot  from the CSV because it has a full time ground from the TTS)

Any comments would be appreciated.

[ja17]

Yes some starting problems can be caused by an over-rich mixture. As long as you are not sunning rich all the time you should be fine. Realize that the latest versions of the M130 mechanically injected engines had no solenoids at all on the injection pump! Your next test will be to see how it does starting in very cold weather. During frigid cold temperatures both starting aids are maximizing fuel supply for cold starting.

[gordon]

12C temperature overnight so not very cold but car started first turn this morning with the injection pump solonoid still disconnected I guess that I now need to check the cold start device ( shims, plunger positions  etc) and adjust the mixture as per  the Tube video. Currently tickover is about 1100 revs but at least it now starts easily from hot.

Thanks for all your input, where would I be without it,