2 days ago I decided to do my semi annual coolant change and after I finished the job I have been experiencing a hard start issue. I have had no issues until I performed the job.

It is a 1995 LT1 Z28. The steps i took during the job was I disconnected all the hoses and flushed the engine and radiator with a garden hose because the lower drain plug on the radiator had broken off. after refilling the sytem i acidently knocked the IAT sensor wire off while bleeding the cooling system and got the sensor wet. Is there a possibility that the coolant can be affecting the sensor and has forced this hard start condition. Also would water intrusion into the Optispark be causing this same problem. When I crank the engine it acts like a weak spark condition and is causing the engine to flood. While it is running i dont experience any other issues like misfires or overheating. Any help would be appreciated!

 

Unless you spilled a lot of coolant on the opti, I don't see this causing the problem.

Knocking a sensor loose wouldn't cause a hard start issue, as they would only affect driveability and the car would still fire up fine.

The only things that can prolong starting are:

Worn/dirty/fouled plugs
Moisture in the ignition system - Opti, ICM
Weak fuel pump
Clogged fuel filter

Forget a sensor causing it.

If you spilled coolant on your opti and it's a bad hard start you might want to give it a good cleaning or even take some compressed air to it to blow the coolant out.

 

Check the coolant temp sensor in the water pump.

 

Typically when these go bad it doesn't affect starting.

IIRC this has no bearing on the ECU until the car reaches operating temp.

 

So tell me then...how does the PCM (not ECU) know when the motor has reached operating temperature? Hmmm?

 

When you first start the car the ECU disregards sensor activity and remains in open loop (rich condition). Once the coolant reaches operating temp, if the coolant sensor is working properly, it will send a signal to the ecu and adjust fuel delivery to a stoich mixture.

If the sensor is bad, it could leave your car in open loop, causing a constant rich condition, or as I've seen a few times, when it reaches operating temp, lean the car out to where it spits and sputters and will barely hold an idle.

Actually, you could unplug that sensor on the water pump and the car would start and idle fine for a while - I did it while diagnosing an extremely lean condition in the past.

 

The PCM uses the coolant temp to set the cold-start enrichment (A/F ratio). Do you think that telling the PCM the engine is ice cold when its not, or very hot when its not, might cause starting problems? Did you ever tried to start a carb engine with a faulty choke?

PCM also uses the coolant temp sensor to set target idle speed. Also uses it to determine when to switch to closed loop.

 

Where did you come up with this BS. When the engine starts, the PCM (or ECU as you want to call it) uses ALL the sensor input EXCEPT the O2 sensors.

 

 

I thought I read that in the past.

So that sensor will effect the starting of the car?

 

yes

 

Rofl.... Injuneer does it again. If there were a LT1 god award, he would get it. Besides Injuneer's suggestion on the coolant temp sensor, I do have to wonder if you spilled a lot of coolant on something electrical, though. Did you notice any really wet areas right after changing the coolant?

 

Since i had no way of draining the radiator and had to remove both hoses and perform a " Back flush " the front of the engine did encounter alot of water. Also while i was bleeding the air while it was idling the thermostat housing bleeder allowed ater to spray onto the IAT sensor and when i un;plugged the sensor insite the housing was wet from coolant. I plan on spending tomorrow doing some more in depth troubleshooting and will find the source. Thanks injuneer for clarifying the coolant sensor operation for me and how the ECM utilizes specific sensors at cold engine operation. I will post what i find!