Why is extra fuel for cold starting added via the cold start injector + IAC passage?

Why wasn't the extra cold start fuel supplied via the normal injectors?

Maybe it was too easy to overinject fuel via the normal injectors and flood the engine with liquid fuel?

Perhaps by spraying liquid fuel in the IAC passage, puddling/accumulation in the ports is eliminated. Fuel vapors rise through the six holes and enter the runners, with less flooding risk.

I suspect that the cold start injector gave a wider tuning window versus simply using the normal injectors. I suppose that later on the tuning expertise was developed to allow for throwing away the cold start injector.

GM use that on some early Port EFI not sure why.
It's auto feed starting spray.

Is only on in cold weather and run in parallel w/ the starter control by the Ignition switch in the cabin.
CSI Switch is thermal and doesn't run above X°F(Y°C) Temp is covered in some charts in 85-87, maybe 88, Fiero FSM. (Told GM deleted that for 88 along w/ other 88 changes...)

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The ECU probably doesn't have enough processing power for it. The Fiero ECUs are pretty primitive.

Being a rather old mechanic (engineer) now, I have worked on some rather old cars in my time😉
The early '70s injection systems, like Bosch K and L-jet injection always used a "simple" thermo governed extra cold start injector.
As was said before, the systems were primitive so alot of "mechanical" or hard wired components were used.
They (the ECUs) were probably just not that fast enough or tunable at the time.
Regards,
Rafe

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"Turbo Slug" - '87 Fiero GT. 3800 turbo. - The fastest Fiero in France!
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quote Originally posted by Blacktree: The ECU probably doesn't have enough processing power for it. The Fiero ECUs are pretty primitive.

Yep I'd blame 80s technology as well.

Unless the Fiero processor was already the top-of-the-line unit available (doubt it), it seems like it would be cheaper overall to spend a bit more on a more capable processor and save the money on the cold start hardware.

For that reason, I'm not convinced of the limited processor idea... there must have been some other motivating factor, such as "that's the way things are done, lets not deviate from the standard too much".

Likely Is Not a "Slow" ECM CPU or other ECM problem.
Other "Primitive" ECM have same CPU but different injector system types.

IS Likely involving...
Programing the Fuel mapping in the ECM.
The choice for main injectors for Batch Firing them for V6 and V8.

Again the dumb CSI is only to start when Cold to Very Cold. In warm to hot weather the injector barely runs or not at all...
In Fiero (and others w/ same engine) FSM "CHART A-9, COLD START VALVE TEST, 2.8L "P" SERIES (PORT)"

quote The circuit is activated only in the crank mode. The power is supplied directly from the starter solenoid and is controlled by a cold start switch, which provides a ground path for the valve during cranking when engine coolant is below 95°F (35°C). The cold start fuel injection switch contains a bimetal switch, which opens at a specified coolant temperature. This bimetal is also heated by the winding in the cold start fuel injection switch, which allows the valve to stay "ON" for 8 seconds at -20°C (-5°F) coolant. The time the switch will stay closed varies inversely with coolant temperature. In other words, as the coolant temperature goes up, the cold start valve "ON" time goes down.

This subsystem will give bigger "starting fluid" shot as weather temp drops w/o having more complicated fuel maps in the ECM.
Will basically act like someone hit the gas pedal for Carb engines.
And that 8 seconds max If you turn the Key for 8+ seconds too. When turn the key less then whatever max the CS switch "thinks" the injector is Off regardless.

Many people block/remove them but can be hard to start in cold weather making problems for the cold battery and starter motor spinning engine w/ cold oil etc. IOW You better have the best battery (high CCA rating) and good starter when weather is cold or freezing as is, more so DIY deleting the CSI on cars w/ them.

[This message has been edited by theogre (edited 10-06-2021).]

quote Originally posted by theogre:b Many people block/remove them but can be hard to start in cold weather making problems for the cold battery and starter motor spinning engine w/ cold oil etc. IOW You better have the best battery (high CCA rating) and good starter when weather is cold or freezing as is, more so DIY deleting the CSI on cars w/ them.

My previous owner deleted mine, he didnt even bother to clean out the metal shavings from retapping the threads. As with starting I havent had any issues with starting below freezing, altho the coldest its gotten is like 25 degrees. I imagine at -10 degrees it would be like trying to start a carbureted car without a choke.