Been a while since I've been here, but long story on the truck, it was a 96 with a stock 318, motor blew and I dropped a 98 360 in it. Did a full rebuild on it, ecu flashed to a 98 360 via vin. Really the only problem is the temp sensor is pegged to the right all the time. Now the 98s intake manifold deleted the sensor that the 96 had which I relocated to an inline hose splice. Sensor, along with every other sensor on the motor is new. Any ideas where to start?

 

Did the '98's have 2 sensors?
Might not need both. Or could have
got a bad one.

 

98 intake manifold has one, I think. It's right behind the alt and only has one wire. The 96 has that one plus one tapped into the manifold between the alt and a/c comp.

 

Sensor should have two wires in the manifold.....

Sensor for the gauge is one-wire. Hence, the sensor needs a ground as well.

 

One worked the gauge the other was the sensor for the pcm. In 98 i think they just used one for both. May need to swap intakes. Good time to do the plenum repair!
You need to do some comparisons from the two years. Wiring and sensors. The two wire sensor could be a two part sensor. Usually the motor is used as the ground in the single wire set ups. Not sure if the second wire is a ground or not.

 

On the two wire sensor, one wire is a 5 volt reference signal, the other is the sensor signal going back to the PCM. Check out the wiring diagrams, they will confirm that.

The one wire sensor does indeed ground thru the engine though. So, if it is isolated in a hose, it simply won't work. Need to have a ground path. (although, If it wasn't getting any ground, I would think the gauge wouldn't move off Cold, not be pegged out.... something is strange there.)

 

Unless without a ground (0 volt reference), it's trying to ground though the gauge (signal wire) and only seeing 5 volts.

Generally, inline sensor adapters have a screw for a ground wire.

 

Single wire sensor is still in its stock location. Two wire sensor was put in the splice

 

Disconnect the single wire connector, and see if the gauge bottoms out.