02 to 99 3.8L Swap

[rjb]

I dropped an '02 3.8L and tranny into a '99 (was also a 3.8L). I noticed a couple of small differences on the wiring so I also used the '02 wiring harness.

The motor fired right up but I have a few small issues:
1. The cooling fan immediatley comes on and stays on
2. The temperature guage does not work (worked before)
3. The A/C will not engage (worked before)

I'm not quite sure where to start looking. I'm hoping that it's something fairly simple. Any suggestions are appreciated.

 

[wmburns]

The 02 motor has a CHT where as the 99 has a ECT senor. What did you do about the difference?

Since you used the 02 harness, likely this means that the CHT sensor is being forced feed to the 99 PCM as the ECT sensor. This is causing the temperature problems because the output of the CHT is different from the ECT.

The AC is likely not working because the PCM disables the AC when temperature related DTCs are present. This is by design to protect the motor.

When performing motor swaps it generally the best idea to keep the electronics of the original motor.

If you need a set of Ford wiring diagrams and workshop manuals for your car, I maybe able to help. PM if interested.

ECT=engine cooling temperature. Sensor located in contact with the coolant.
CHT=cylinder head temperature. Sensor located in the metal jacket of the head itself.

 

[rjb]

Yes, the biggest reason that I used the 02 harness was because of the temp sending unit. It's on the back-side of the head on the 02 and it's near the water pump neck on the 99.

Yesterday, I grabbed my multi-meter and started chasing wires.

On the 99 harness, I found the temp sensor on Pin 16 of the 42-pin connector. On the 02, I found it on Pin 5. I pulled it from Pin 5 and moved it to Pin 16 (which was empty on the 02 harness).

Now when I fire up the motor, everything appears to work fine. The cooling fan doesn't immediately start running, the AC works, and the Temp guage appears to be working.

So do I need to switch the 02 motor from CHT to ECT or will the 99 electrical system be able to handle it?

I haven't hooked up the oxygen sensors yet. I think that I will need to move another pin for those to work properly.

Thanks for the reply.

 

[wmburns]

A novel solution to the problem. However, I have no idea if the resistance curve of the CHT is compatible with the curve of the ECT. You are going to have to compare the graphs in the workshop manual to know for sure.

Most ppl would move the ECT from the original motor to the new in order to keep with the electronics that the PCM is expecting.

You are on your own.

If you need a set of Ford workshop manuals, wiring diagrams, and PCM manuals for your car, I maybe able to help. PM if interested.