Cold Start Enrichment Circuit On 2.4 911T?

[73ess]

I've searched the forum on cold start enrichment for MFI 911's, but couldn't find any posts with enough detail. Can someone explain in detail, how 12V gets to the cold start enrichment solenoid that sits on top of the fuel filter in a 2.4 911T with MFI? Should I see 12V at the solenoid, after I turn the key to the ON position or only while cranking the starter? What other components are between the ignition switch and the enrichment solenoid? Thanks!

[toms73]

I am not an expert but I have been chasing the same system.This is what I have heard There is a solenoid black round in the engine compartment below the three fuses, this controls the duration of fuel flow. In order for the system to operate the temp sensor on top of the engine must ID the engine as being cold and the hand the hand throttle must be engaged enough to turn off the fuel shut off solenoid. mine was disconnected I believe for safety reasons. Older models injected fuel into the air box and if proper starting procedures were not followed the build up of fuel would cause a fire burning, down the Porsche not a happy song. The fuel lines to each cylinder had not been used in SO long they leaked. I am now replacing them and will see if I like it better with the system hooked up.
73 911 T Targa

[howard freeman]

Terminal 50 start only power runs to the thermo time switch mounted on the crankcase breather housing. The 2nd wire on the thermo switch runs to the solenoid on top of the fuel filter. Its is only activated at temps under 40 degree C. or 104 F. So the only time you will see 12 volts there is when those conditions are met. Been a long time since I worked on a MFI car.
Howard

[dicklague]

I have a push button on my dash that grounds a relay the supplies +12vdc to the solenoid.

I thinks lots of MFI guys do this.....this way YOU control it!

[Porboynz]

12V is fed from the ignition key when in the starter cranking position (its the starter solenoid feed). This 12V is fed via the thermostat to the cold start solenoid. The fuel shut off is not part of this circuit on my 911, thats a different circuit designed for over run fuel cutoff fed via an RPM sensor and microswitch on the intake stacks (avoids back firing in the exhaust, most of the time) Make sure your fuel filter assembly is properly earthed as its rubber mounted and depends on a short earth wire to the body stud behind the filter assembly for correct operation. The switch on the dash makes sense as well, but the Porsche system works OK except when the car is not quite warm enough for the thermostat to deactivate the cold start solenoid and its easy to over fuel the engine. Half throttle helps in this case.