Okay. A question for you Fiero gurus. (Are you listening, Ogre?)

Can some one explain the purpose of the Air Charge Temp Sensor & Cold Start Injector Switch? Seems like they do similar functions, initially but as the engine warms up, the Cold Start Injector Switch disables the cold start injector so the engine doesn't run overly rich. Am I on the right track?

Also, it appears the cold start injector switch is no longer available. Does it operate the same way that that the fan switch operates, except backwards where a rise in temp opens the circuit? Does anyone know of a replacement?

(edited for grammar)

[This message has been edited by Mike in Sydney (edited 06-03-2024).]

The 2 have Nothing do to w/ each other.

cold injector only runs weather cold = engine cold during starting. the switch does even start to closes until engine coolant < ~ 50°F

ECM use the other along w/ more sensors to run the engine.

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

[This message has been edited by theogre (edited 06-03-2024).]

This is for the V6, but I don't think any of the 4cyl TBI cars use these.
The Cold Start Injector and the Cold Start Switch are an analog system invented by mad scientists from the 1950s. The newfangled 1980s ECM contraption is not connected to them and doesn't know they exist. However, the tuning of the ECM was calibrated to work best while this system is present.


The cold start injector can only be powered while you are cranking the starter *and* the cold start injector switch is cold enough to complete the path to Ground, closing the circuit.
The Cold Start Switch will only close the circuit while it's temperature is below some threshold. It has a heater built into it, so as you crank the starter, the Cold Start Switch will heat itself above the threshold quickly.
It has an effect even in warm weather. In cold weather it operates longer though because it begins at a colder temperature, so the Switch takes longer to heat itself above the threshold.

It's purpose is to aid starting the engine, and that's all. The CSI is disconnected from power when the key is released.
It is *not* involved in how the engine runs after it has started, unless the cold start injector (not the switch) is leaking.

The cold start injector sprays a more broadly distributed mist than the port injectors do, but it might not be well balanced between cylinders. The intake on the V6 wasn't designed for TBI, which is basically what the cold start injector is imitating.
Yeah, it's weird.
Some may consider it optional in warm climates. But I tried disconnecting mine in warm summer weather and it made the engine take a lot longer to start, so I plugged it back in. It might be possible to tune the ECM to start better without the CSI - but in a few attempts I didn't get anywhere and lost interest.


The intake air temperature sensor (in the air cleaner) is used by the ECM for fuel calculations. You can test it with a multimeter using this chart (I don't remember where this originally came from):

Mine was way off, but after soaking it in CLR it got back into line. Don't rely on ever seeing an error code because the rules for setting those codes are very simple, and generous.
According to the manual you'll only get a code if it reads below -22F or above 275F. Mine sitting at ambient was reading in the low 200s F, the ECM thought that was reasonable.
The sensor (and the air in the intake) does soak up heat when you're idling, so to be fair they did have to make some allowance for that, but I think they overdid it. When you're in motion, the incoming air and the sensor reading quickly cools back down.

[This message has been edited by armos (edited 06-04-2024).]

quote Originally posted by armos: This is for the V6, but I don't think any of the 4cyl TBI cars use these. The Cold Start Injector and the Cold Start Switch are an analog system invented by mad scientists from the 1950s. The newfangled 1980s ECM contraption is not connected to them and doesn't know they exist. However, the tuning of the ECM was calibrated to work best while this system is present.

Nope. ECM knows Nothing about CSI at all.

CSI is basically = to Carb w/ Auto Choke (that also knows nothing about the choke working or not) because some ECM skipped programing for this or other issues that CSI "solves" cold start problems.
Other ECM have programing for easier starting when cold & why some "upgraded" this V6 version to use a "newer" ECM for this & other reasons.

Even Dukes can take longer to start when cold but often isn't for fuel but ECM turning On fuel injection because ECM/PCM need to see ignition before starting injector(s). Example: 87+ DIS Dukes often "needs" a long crank when "cold." But turn the key to start, back off, try again often will start noticeable faster then 1 long crank. That's even when have a Wells ICM that's claim their unit is faster starting vs GM units.

If have iffy air or coolant temp sensors etc will cause problems & often won't set Codes. Could test some w/ Ω meter but best is ECM scanner that see iffy sensor but also iffy wires causing bad data. see https://web.archive.org/web...~fierocave/ecmqa.htm

Related "Fiero" V6 part often deleted is heater loop running thru TB. Is there to prevent "Carb Icing" that causes problems & w/o warning. Others use Thermac air heating by the exhaust pipes. Icing can happen regardless of weather temp or relative humidity because of air flow thru the TB/TBI/Carb body drops the temp in it. Example: I had old Gen 1 Dodge Caravan that Iced on the road stopped @ longish traffic light because Thermac pipe fell off the air cleaner. Engine was Hot, Weather above Freezing, but that day had somewhat high humidity. Engine stalled, ice melted, so could start & pull over w/o causing traffic problems. You see some Racers etc w/ blowers that spray alcohol on butterflies for same reason & even that fails sometimes.

quote Originally posted by armos: The cold start injector can only be powered while you are cranking the starter *and* the cold start injector switch is cold enough to complete the path to Ground, closing the circuit. The Cold Start Switch will only close the circuit while it's temperature is below some threshold. It has a heater built into it, so as you crank the starter, the Cold Start Switch will heat itself above the threshold quickly. It has an effect even in warm weather. In cold weather it operates longer though because it begins at a colder temperature, so the Switch takes longer to heat itself above the threshold. It's purpose is to aid starting the engine, and that's all. The CSI is disconnected from power when the key is released. It is *not* involved in how the engine runs after it has started, unless the cold start injector (not the switch) is leaking.

Thanks, Armos. Appreciate the explanation.

The connector on my '86 SE has become broken due to age and heat. I've been looking for a replacement CS sensor. The AC Delco part number is 212-312 and it's no longer available. There are NOS units out there but thaey are US$125 or more. I'm trying to understand how it operates to see if another sensor (like the radiator fan switch) will work.

From your description, I don't believe the Fan Switch can be used. What you describe is a normally closed switch that opens when the engine temperature rises. I believe the fan switch is normally open and closes when the temperature rises activating the fan.

I'm having issues when starting the car when it is cold, even in summer. After coming up to temp, the car starts pretty easily. When cold, it is stubborn but a shot of starting fluid will fire it right up. THat's whay Im leaning towards an issue with the cold start system.

I used to have an old Citroen CX gti that had a similar cold start system, with an extra injector that sprayed into the plenum.
If you can't find the switch for GM cars, you may be able to get a similar switch for an older european car. One that uses a Bosch K or L-jetronic injection system?

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"Turbo Slug" - '87 Fiero GT. 3800 turbo. - The fastest Fiero in France! @turboslugfiero
https://youtu.be/hUzOAeyWLfM

Good to know Frenchrafe for the cold start switch
Do you know if some european car have the EGR solenoid similar to a fiero V6
Me I dont need one but i know some PFF members need it

quote Originally posted by Mike in Sydney: I'm trying to understand how it operates to see if another sensor (like the radiator fan switch) will work. From your description, I don't believe the Fan Switch can be used.

Correct. "Fan" and most Thermal switches won't work.

CSI Switch operated when coolant is cold.
But when it get power thru starter solenoid circuit... That Heats the Switch as well as running the CSI.

This limits fuel vs temp & stops running CSI after ~ 8 sec Max, can run shorter if engine is warmer.
Prevents "flooding" as take some time to cool it to run again.

Switch start CSI when coolant < 95°F 35°C

The CSI won't work can be electrical or plumbing like crap in the injector.

Many think can just put volt meter across the injector plug but...
Have volts but not load so may not turn off as expected.
If you short the injector plug, the switch can fry before the fusible link.

Can use Pressure gauge to watch it better. Get FSM etc. Summary:

quote Originally posted by claude dalpe: Do you know if some european car have the EGR solenoid similar to a fiero V6 Me I dont need one but i know some PFF members need it

No, EGR was an american thing long before it was imposed to europeen cars !
Only high end cars had fuel injection. We carried on using carburetters and very little emissions control right up untill the '90's

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"Turbo Slug" - '87 Fiero GT. 3800 turbo. - The fastest Fiero in France! @turboslugfiero
https://youtu.be/hUzOAeyWLfM

quote Originally posted by armos: However, the tuning of the ECM was calibrated to work best while this system is present.

quote Originally posted by theogre: Nope. ECM knows Nothing about CSI at all.

The ECM has a table that controls the amount of fuel it commands from the port injectors during cranking. It varies according to temperature from the Coolant Temperature Sensor. I haven't messed with it enough to swear that the table works, but it's there.
The values in that table, or any other programming that involves cranking fuel, would have been calibrated for the target application - a car where the Cold Start injector is working. Without the CSI, the factory tune doesn't give enough fuel while cranking.

quote Originally posted by Mike in Sydney: I'm having issues when starting the car when it is cold, even in summer. After coming up to temp, the car starts pretty easily. When cold, it is stubborn but a shot of starting fluid will fire it right up. THat's whay Im leaning towards an issue with the cold start system.

When I tried unplugging my CSI in warm weather, I had much longer crank times, but it would start in around 5-7 seconds I'd say. Long enough to be annoying but it wasn't difficult. Once it started, it ran normally. I had WinALDL hooked up when I was messing with this so I know the sensors were all fine, it just wasn't getting enough fuel quickly enough. I made a couple wild guess edits to that table, then gave up and just plugged the CSI back in.

If you only have longer crank times, then a CSI issue is possible. You mentioned a broken connector, so maybe it's just not making contact.
But if it's especially difficult to start (not just annoyingly slow), or continues to be problematic on repeated starts, or if you need starting fluid in warm weather, or it has any issue with how it runs after starting, then you probably have a different issue. Like Ogre suggested it could be another faulty sensor, such as the coolant temperature sensor. That resistance chart above can be used to check whether that sensor (and the intake air sensor) are accurate. Try checking them while the car is sitting at ambient, so you know what temperature and resistance to expect. They should read close to the same.
WinALDL on a laptop is even better, since it shows you everything the ECM is seeing, but a resistance check on the sensors is simpler to do.

GM also used the CSI system on some V8 cars, like some 305 TPI Camaros. The injector is almost surely different but there's a chance the Switch component could be the same - I don't know.