MFI starting enrichment temp sensor - '73 911S

[Boulder Bob]

I suspect the subject part is not working properly. Does it change the amount of fuel that gets squirted depending upon the temperature? Can someone please provide a part number and tell me where it is located?

thank you very much!

[LKreg]

I think this is what you are referring to...maybe an expert can provide the info you need.

[blucille]

I'm sure someone can post a photo.....but often it is a failure of the double-hose (hose within a hose) that goes from the heat exchanger to the temp sensor....the hose ends sort of to the rear (of the car) of the MFI pump, or head up from the ignition distributor....basically the top of the fan housing, on the left side.

so, the temp sensor senses temp of the heat exchangers, the factory put one of those cardboard hoses (now likely superseded to vinyl) inside another one of those hoses....if the outer hose fails, the temperature readings are inaccurate....otherwise, they often get replaced with any ordinary hose that a mechanic has laying around.

[blucille]

here's a good photo of the hose I had in mind, attaches to the thermostat on the MFI pump, the hose passes thru the ignition coil wire

http://members.rennlist.org/analogmike/myengines.jpg

[beh911]

I suspect the subject part is not working properly. Does it change the amount of fuel that gets squirted depending upon the temperature? Can someone please provide a part number and tell me where it is located?

thank you very much!

I'm no expert and will be corrected if what I write is not correct, but I believe the thermo-time switch (correct part# 911.617.117.00 as provided in pic above) closes the circuit (opens the enrichment solenoid) on a metered time basis but does not affect how 'open' the solenoid is. The enrichment solenoid (on the MFI pump) is what is opened per the current from that sensor in the crankcase cover. Make sense?

The sensor (thermo time switch) is located in the crankcase breather cover, centerline of engine, underneath your air intake assembly, on the left, at the back (front of car) of engine. It works within a certain temperature range

What symptoms are you experiencing?

[Boulder Bob]

cold ambient (< 60 deg F) starts pretty well (one second of cranking, stop, count to 10, crank again, fires right up) - hot ambient, cold start (90 deg F) starts crappy (lots of cranking and runs poorly for 30 seconds)

"hot Start" (within 20 minutes after full warm up) starts great

"warm start" (hot day after sitting for 2 hours) starts crappy

I follow the starting procedures as outlined in the owner's manual

thanks for the help

[RSTarga]

with the gas these days, i always pull up the hand throttle to start when hot also. I think, but stand to be corrected, that the fuel boils off in the line vapour lock, due to the heat and the alcohol in the fuel.

[cmcfaul]

I am a bit confused, What tells the cold start not to work when the engine is hot? A picture would be great.
I hooked up the cold start (on top of the fuel filter) to the starter circuit. Engage the starter and power goes to the cold start thing on top of the fuel filter. Works great when cold but can flood when hot.

[beh911]

I am a bit confused, What tells the cold start not to work when the engine is hot? A picture would be great.
I hooked up the cold start (on top of the fuel filter) to the starter circuit. Engage the starter and power goes to the cold start thing on top of the fuel filter. Works great when cold but can flood when hot.

What year is your car?

In short, the temperature sensitivity of the cold start valve and/or enrichment solenoid depends on the thermo time switch. This switch says 'too hot to engage'.

I'm not experienced enough to speak too strongly, but I would be concerned with your current setup connected directly to the starter circuit. Someone will comment probably.

For 69, there are two switches, one for the solenoid on top of the MFI assembly and one for the enrichment solenoid on the pump. For the 2.2 engines, the two switches went away. Here is the factory manual's explanation of the thermo-time switch:

[mrg3.6]

I'm sure someone can post a photo.....but often it is a failure of the double-hose (hose within a hose) that goes from the heat exchanger to the temp sensor....

As an ancillary question on the same subject, I am just about to swap out my heat exchangers for headers on my 2.7 mfi so how do I deal with the enrichment circuit?

Thx

Martin