FI coolant temp sensor issue.

[wizard124]

For a while now, my 1980 FI would experience engine stalling/missing. One drive would exhibit these traits while the next drive would be without symptoms. This would mostly occur in the 3k to 4k rpm range. Very frustrating! It was hard to tell if it was fuel pressure related or electronic.

I took it out for a drive 2 days ago and the engine symptoms were much worse. These included surging under full throttle acceleration, engine dying under clutch depressed coasting to a stop, rough idle, lack of power, etc. It also stopped running and it was about 10 minutes before I could get it restarted and nursed it to my home.

My troubleshooting included the following steps without result: 1) Swapping the fuel pump control relay. 2) Inspection of distributor cap, rotor and centrifugal advance. 3) Pinching off the fuel line to the cold start valve. 4) Removing the connector from the ECU and reading the resistances of the air flow meter. There are 4 steps to this as outlined in the Fiat FI toubleshooting manual. All resistances were reasonable with the specifications given as these resistances vary with temperature.

I also checked the resistance, at the ECU connector for the Coolant Temp Sensor. This is the sensor located on the coolant tee at the very front of the cylinder head. The resistance read 168,000 ohms! It should be 2100 to 2900 at 68F. I then removed the plug at the sensor and read the sensor resistance directly to be 2380 ohms. So, my sensor checked good! Fortunately, once I re-plugged the connector and read the resistance at the ECU, I obtained the same result!

All I can surmise is I had a bit of corrosion on the terminals or the plug had worked itself a bit loose. The test drive went great.

[spider2081]

yes the connectors do corrode. So that may very well have been the issue. Did you use a contact cleaner on the connector? Often that will post pone future corrosion issues with the contacts.
Sometimes the temperature sensors themselves are intermittent. It might be wise to purchase one and have it in hand in case the problem reoccurs.

[wizard124]

Part of that coolant sensor connector had broken off at some point but it still connects with a snap. It wasn't a problem until it became a problem. I didn't use any contact cleaner. Once I reconnected it to the sensor, I had good ohm readings at the ECU plug.

3 zip ties later and a secure connection, all is good! I just ran about 45 miles, taking my wife to lunch, and she is purring like a kitten.

I had the car non-op in California because I was sick of the smog checks so it sat for a while. I'm in Wyoming now so I am happy to have the car running well. They are so much fun to drive. 40 to 60 mph on twisting country roads is my happy place!