Coolant Temp Sensor causing rough idle and low power?

[searya]

I have been chasing a problem for a while with my 1984 Pini Azzurra. The car worked perfect driving home the night before but the next day it ran rough and had super low power (missing, backfiring etc).

Today I unplugged the Coolant Temp Sensor (in the front of engine in between radiator hoses) and the car ran MUCH better. It would now idle fine and it would drive fine to about 2500 rpm. At 2500 RPM it would still lose power. Anyway, I told my wife that I am staying in the garage until I find the fix so any help would be appreciated.

The Coolant Temp Sensor (in the front of engine in between radiator hoses) has already been replaced so it is brand new (wires are still old though so checking those now)

Here is what I have done so far:
1. Replaced Spark Plugs (and gapped to spec)
2. Checked for vacuum leaks (everywhere except I don't know how to check inside the brake booster)
3. Checked timing with a timing light
4. Cleaned Throttle Plate
5. Check spark plug wires for arcing
6. Replaced Fuel Pump
7. Replaced Fuel Filter
8. Checked vacuum thingy above rear axle
9. Checked Charcoal Canister and hose for breaks (and fixed some)

[searya]

So some new info that I determined after my first post:

I continue to work through the FI Troubleshooting guide.

I retested Fuel Pressure at the cold start injector hose which as at 35. Since it was low I went to the next step which was to pinch the return line with pliers and see if pressure increased. I definitely did as it shot up to 80psi. Right when I let go of the pliers it jumped back down to 35 psi.

So assuming I need a new Fuel Pressure Regulator?

Also, I wanted to see if there was a break in the coolant temp sensor line so I did the following and would love to know if that confirms a good wire to the sensor:

I put a paper clip in the end of the pigtail connecting the two pins. Went back to the ecu and checked ohms using ECU pin 13 and a ground. I got 3.5 ohms. I also did the same test on the old pigtail I cutoff but this time instead of checking the ECU put the paperclip in and tested the ohms on by putting the black and red multimeter points on the cut wire. Also got 3.5 ohms.

[RRoller123]

35 is good pressure for the FI system

[searya]

Thanks! So looks like either one of my Fuel Pressure regulators are good.

Still runs way rougher with the coolant temp sensor (on the front of the engine) plugged in. I swapped back to the old one and still same problem. So figuring if a brand new sensor and an old one didn't make a difference then it would have to be the wiring to it.

I don't know much about electrical testing so to check to see if there was a break in the wire I did the steps below. Would that confirm my wire is good?

I put a paper clip in the end of the coolant temp sensor pigtail connecting the two pins. Went back to the ecu and checked ohms using ECU pin 13 and a ground. I got 3.5 ohms. I also did the same test on the old pigtail I cutoff but this time instead of checking the ECU put the paperclip in and tested the ohms on by putting the black and red multimeter points on the cut wire. Also got 3.5 ohms.

[spider2081]

I assume you are using a digital volt/ohm meter, if this is the case have you touched the meter leads together on the most sensitive (lowest) ohms scale. 3.5 ohms could be the lowest value you meter can display with the leads you are using. In other words this is your meter/leads will display for zero ohms.
Have you measured the resistance ot the coolant temperature sensor before starting the engine (cold engine) and then again when the engine is at operation temperature of 190 degrees At 70 F resistance should be about 2000 ohms at 180 degrees F resistance should be around 300 ohms

[searya]

I tried that with the sensor plugged in from the computer and go nothing ohm wise with both the original sensor and and a new one that I bought.

That made me think there was a break in the wire hence the reason I looped it it at the end of the pigtail and then got 3.5 ohms.

I assume you are using a digital volt/ohm meter, if this is the case have you touched the meter leads together on the most sensitive (lowest) ohms scale. 3.5 ohms could be the lowest value you meter can display with the leads you are using. In other words this is your meter/leads will display for zero ohms.
Have you measured the resistance ot the coolant temperature sensor before starting the engine (cold engine) and then again when the engine is at operation temperature of 190 degrees At 70 F resistance should be about 2000 ohms at 180 degrees F resistance should be around 300 ohms