When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Hello, I have been having trouble with my car stalling after cold starts. I unplugged the cold start injector this morning and it took longer to start, but ran fine with it unplugged. I am wondering if I can get away with just leaving the injector in there and unplugged. A tidy engine isn't all that important to me. I am also wondering if getting the computer reprogrammed or getting a prom from a 3.1 engine will help with the extended starting times. I have an 86 firebird with a 2.8 and automatic transmission.
The cold start injector gets its power (+12v) from the ignition switch side of the starter solenoid.
On the front of the engine close to the thermostat housing and next to the Coolant Temperature Sensor there is a cold start switch or coolant temperature switch that sends the ground to complete power the cold start injector. Below is from another post on how the cold switch works. It only works when engine is cranking.
This from an older post on the forum V8 section. The cold start injector on the V6 works the same way.
This is how the cold start injector works:
The ground side of the cold start injector runs through its own coolant temperature switch that's located in the intake manifold below the thermostat. The temperature switch also contains a heating element that limits the time the injector is "on", inversely proportional to coolant temperature - it's on more when cold, on less when the coolant is kinda cold (within its operation range).
The cold start injector turns on only when the ignition switch is in the start position and the coolant is "cold"; the temperature switch is closed and grounded which completes the electrical circuit.
When the coolant is "hot", the coolant temperature switch is opened. In this case the electrical circuit is opened so the cold start injector will not turn on when the ignition switch is in the start position.
So from what I understand I should try getting a new coolant temperature switch? It seems like the cold start injector is staying on too long and is causing the engine to stall. Is this the right sensor?
Ricks Camaros shows it is out of stock with a price close to $300. If a new one is available it would be expensive. List of GM vehicles that used the same switch at the bottom of post. Someone in the forum said it has a timer built in to the switch so it only operates for 9 seconds.
Check your existing CSS with a meter for proper operation. The switch is closed supplying ground. Below is from Factory Service Manual for V8 but V6 operates the same way.
when the engine is cold but opens around 100 degrees.
+12 Volts DC supplied only when cranking engine
List of vehicles with Cold Start Switch from a member who found a replacement in junkyard on a corvette I should be picking up the Cold Start Switch here shortly. In case anyone was having this issue as well here are the vehicles that the part is on. Same part for the V6, V8 (305 and 350) and the L4
On a cold engine below 100 degrees 12vdc should present on the connector for the cold start injector when cranking the engine. On a warm engine over 100 degrees no voltage should be present when cranking the engine.
Since your car starts it is likely the cold start injector is working even with the voltage a bit low. There are videos of people using a 9 volt battery on a bench to pulse clean injectors. The cold start injector supplies extra fuel only while cranking. Since the voltage is 0 when the temperature is over 100 the cold start switch is doing what it is supposed to do.
You could remove the cold start injector and see if it is supplying fuel but since your car starts it is probably working. Some members have advised against removing the cold start injector because it is hard to get out and back in. The oring on the cold start injector is easily damaged and it is hard to find a replacement.
Would the cold start injector stay stuck on for a warm engine because of a bad coolant sensor or thermal switch? (Cold start switch)
Mine seems to run the cold start scenario every time when the engine is fully warm. It takes about the same rev up time which is really annoying as wouldn’t expect every time you turnover a warm engine.
Appreciate any help as studying this thread and the shop manual. What page number was this from?
Electrically looking at schematic power to timer switch is only during cranking . That’s not to say it can’t be stuck open a fuel pressure test would show drop.
On a cold engine below 100 degrees 12vdc should present on the connector for the cold start injector when cranking the engine. On a warm engine over 100 degrees no voltage should be present when cranking the engine.
I’ll test for this and see if I have voltage on the injector when warm for starters then, thanks 🙏
