MFI AFR at start up

[bliebler]

While cranking at start up, what circuit of the mfi influences starting? Is it the idle circuit because at cranking it is low RPMs or is it the main, because on cold starts, using the hand throttle , or pedal to floor at hot starts, puts the rack at higher RPM position.

I realize that at cold starts the thermostat moves the rack rich but at warm and hot starts it should not influence the rack.

[edmayo]

What year car?

[bliebler]

Ed.
It's a 73S.

[edmayo]

During cranking there is a timed squirt of fuel while the starter is engaged,,,but only for a couple seconds so that someone who grinds away on the starter for a couple minutes doesn't flood the engine. There is NO fuel squirt above 114 degrees engine temp.

[bliebler]

I realize that the cold start system will squirt raw gas, but while cranking, what circuit of the MFI pump influences starting. Is it that only the thermostat and the cold start valve influence starting and the MFI pump is dormant at that time.

[RSTarga]

What problem are you experiencing?

[bliebler]

I'm having problems with warm starts. After driving (oil temp up) and the car sits for 2/3 hours, the car cranks for a long time. Sometimes it cranks for 10 seconds no matter what throttle position I use. When sitting overnight and garage temperature around 50 deg or lower, the car starts right up in 3 seconds which I believe is mostly due to the thermostat as this is true even with the cold start valve disconnected.

[edmayo]

Where are you located? Got ethanol in your gas?

[2.5MFI]

To answer your question on "What circuit of the MFI pump influences starting", it's the thermostat. Except if you have a 69 pump. For the 70 on up nothing else on the pump influences cold starting.

[RSTarga]

If you do a search on "warm starts", you'll see this issue has been discussed quite a bit. I think the conclusion has been that ethanol in the gas is the culprit. The fuel vaporizes in the hard lines. This requires fuel to be pumped back into them.
I don't know where you are, but it gets pretty hot here in Texas so this happens pretty much every time I stop my car and leave it on hot days. Humidity and varying gas quality also affect this.
You sort of have to get the hang of how long you need to let the pump run before engaging the starter, and how far to depress the accelerator when activating the starter.
Usually 5 seconds or so and 1/2 to 3/4 accelerator depression starts it. Don't just crank it forever, if it doesn't start in the first engagement. Turn the switch off and restart, but don't lift your foot off the accelerator and don't pump it.
Practice makes perfect.
Around here the worst times are when they are switching from winter fuel formulations to summer formulation.