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1999 4.3: I started having these issues after I changed the spark plugs. At first, I got a cylinder 3 misfire and after checking the wires I found the #3 wire was burnt through. I replaced all the wires, then popped a CEL for P0118 engine coolant temp sensor high voltage. I replaced the sensor, which worked briefly and then cut out again. I cleaned both connectors and still nothing. With the sensor not working the truck idles roughly and wants to cut power when driving, also it cranks a little longer than usual, but it starts up without too much trouble. I ended up finding a ground strap (i think it's the engine ground) on the passenger side connected high up on the firewall just under the hood. The strap is cut in the middle so I don't know where it connected originally. Can anybody tell me where it connects to or if this could even be the source of my problem?
 

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The truck won't run very well if the ECT sensor is not working because the PCM uses that data to determine how much fuel to inject. It most likely thinks it's -40° inside the engine and pouring fuel in.
Have you considered returning the new sensor since it might just be a bad one? You can test the sensor with an ohm meter. With a cold engine at normal ambient temps it should read a couple 1000 ohms. If it is way high like 250K ohms or way low like 10 ohms, it's bad. The sensor has it's own ground back to the computer. You can also test the wires back to the PCM for continuity with the ohm meter. The yellow goes to C2 pin 23 and the black goes to C3 pin 4.

The ground strap on the firewall bolts to the back of the head. If you feel around you'll find the grounding bolt.
 

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Yep. Itll run in Open Loop (choke on) and foul the spark plugs, thus, rough running.

#3 wire is near the sensor? May have had a high voltage arc-over and destroyed the ECM Temp sensor input. Also, sensors are sensitive to installation torque, make sure to not over-tighten them.
 
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