Hot start issues pole.

[Paul99]

Lots been said about the general hot starting issues as in starts fine cold just not when very hot. 

Lots of different views around the best fix. 

Just wondering which fix gets the most votes!  ??

[Bshaunessy]

MAGIC BULLET:
   A fully functional COLD START SYSTEM ( per tech manual, Starting Aid Tour) will solve most COLD START and HOT START issues.

[ja17]

Good fuel pressure and volume is critical since the circulating fuel keeps the system cool and prevents vapor lock. Gas with Ethanol aggravates the hot starting problems since it lowers the boiling point of the fuel.

[Cees Klumper]

Mine starts very well cold and warm, except when it's been sitting (warm) for more than say 10 minutes. If I restart within 10 minutes it's instant, but much longer and it has to crank a bit longer. Then I usually turn on ignition but wait maybe 10 seconds and let the fuel pump do its thing, then crank and usually it will start up OK. I believe my injection pump check valve(s) are not 100% and allowing fuel pressure to drop in the lines. On cold start, there are those starting aids that compensate for that.
Simplest fix seems to be that manual 'extra fuel through the CSV button' that many have (had) installed.

[rosch]

This solved my hot starting problems in a very easy way .Most hot starting problems originate from a too rich (basic) setting of the FIP .

When engaging the starterswitch with a hot engine EXTRA fuel will be added via the 1 sec. relay by:
a. activation of the CSV
b. activation of the fuel enrichment solenoid at the back of the FIP causing the rack to the full rich position.
So a 2-way further enrichment to an already rich running engine ,causing flooding, thus hard hot start.

This solved my problems:
1. do the split linkage test to get your basic air/fuel mixture correct if required.
2. disconnect the connector from the small round 1-sec relay. Your cold start will not be influenced at all, you only avoid adding extra fuel/enriching when starting a hot engine.
Think of this : would you use the  old fashioned hand choke  when starting a  hot carburater engine?No of course not, it would flood and not start ! So why should you adding so much extra fuel when starting our hot SL engine's ?
3. I added the "extra" the under-dashboard-push-button to manually activate the CSV only when necessary. However did not need it a single time so far....It starts right up without touching the accelerator pedal !

[ja17]

Yes, good information from "rosch". Many hot start issues can be caused by too much enrichment. If you are having hot start problems, try jumping the CSV on the intake during a hot start. If that does not help, then it is likely that your hot starting mixture is already too rich!

[Paul99]

Interesting that it may be TOO much fuel during hot starting, always felt it was fuel starvation due to the hotness and the fuel evaporating and not getting through.

A similar (sort of) situation is with another car I have with a holley double pumper carb. On hard braking the engine would stop.  I thought it was again fuel starvation, but it turned out it was fuel flowing from the rear float chamber and flooding the engine. I lowered the float level a lot on the rear chamber and the problem went away.  Less fuel was the answer.

I will try your suggestions.  Many thanks. 

How boring modern cars are that just start every time!   

[Tom]

Timely topic. Today’s temperature in Alexandria, Virginia topped 101 Fahrenheit.  My car stalled at two stop lights. Never does this in normal conditions.  I’m afraid 100 in the summer is the new normal so I will need to figure this out.

[ctaylor738]

My early 230sl is almost impossible to start when hot.  My benchmark is what I call the "stall" test simulating stalling in traffic and needing to immediately  restart.  I also have the 5 minute "stop for gas" test and longer tests. They are all awful.  Long cranks with pedal on the floor, finally firing on one cylinder and then starting one cylinder at a time.  Never any stink out the tailpipe.  Plugs look perfect.  Pressure and flow not great but in spec. No difference in fuel flow between hot and cold.  Electrics check out.  Always has spark.  Pump solenoid and cold start valve can be activated manually but don't seem to help.  Cold start valve and short fuel pump are new. 

Obvious to me that the injection pump cannot deliver enough pressure to open the injectors on the hot start.

[primal scream]

CT

[rosch]

@ctaylor738

Sounds to me you might have a problem with "vapor lock" Check if your FIP gets hot after some driving, indicating your fuel circulation (and cooling of your FIP ! ) is insufficient. This may cause boiling fuel and thus air bubbles in your FIP and fuel lines to the injectors.Since your check for fuel volume  is in spec ( I guess you measured it just before the fuel returnline enters the tank ) you might check the returnline part within the tank towards the flowerpot for clogging, resulting in poor circulation.

[wwheeler]

On my '68 280SE, My hot starts were the same as above. Instant restart OK when hot. But anytime between that and an hour was difficult. I did a million tests and then zeroed in on the starting magnet. When I disconnected that, hot starts are great. Reinstall, hot starts are terrible. My later cold start system is different than the early 230SL, so I don't have the small round timer. Cold starts need more fuel with the starting magnet and I solved that by adding the manual cabin switch. The manual switch basically replaces the starting magnet function. All is good now.

I left wiring so that the CSV operates normally while the engine is cranking. I operate manual switch when the engine is not cranking. That is actually an advantage in that the fuel is sitting there in the manifold waiting for the engine to suck it in. Engine fires very quickly cold with that set up. It takes some time to learn when and how much fuel to add manually. I typically activate the cabin switch about 2 seconds when cold and NONE when hot.     

[ctaylor738]

Rosch and Wally:

Thank you for your comments.  In reply:

Fuel delivery, measured at the return line, is the same with the engine hot or cold.  I have blown out the return line several times and it does not feel restricted.

Right now I have the cold start valve disconnected because (believe it or not) cold starts were difficult with it connected.  I have the a momentary switch to ground the thermo-time switch so the pump solenoid operates normally on cold start and I can operate it manual on hot start.  Cold starts are OK.  Operating the switch on hot start does not seem to make a difference.

I understand what you are saying about vapor lock, but can that develop in 2-3 seconds (the Stall Test)?

Cheers,

CT