Will a defective cylinder head temp sensor prevent a car from starting? I have an 86 300 na and I can drive it to work in the morning but that afternoon it wont start. the next morning it will. Ive ran the diags and get a 21 code. My coil was loose and i tightened it - it may have not been grounding? Now, when im driving it cuts out a couple of times but doenst die and seems to be starting fine. I thought it might be a cyl sensor but may be a defective coil?

 

When a car doesn't start it's missing:

#1... proper fuel mix
and/or
#2... spark
and/or
#3... oxygen (air)

Are you getting spark at the plugs? Are you getting fuel? I'm not sure why you'd be checking the CHTS (cyl temp sensor) if the ecu is showing code 21.

 

I thought of it may be a sensor when the car wouldnt start in the evening and I didnt have the ecu out to diagnose. I did check the coil and didnt see any spark. when i did get the car home the next day(it started and ran well) and ran the diags, i got a code 21 but the car did start and i could smell gas.

 

the car will start and run with a bad CHTS. a bad CHTS will make the car run rough when cold, but it will run. you have other problems.