TPS males EL Auto go nuts!
Hi folks, just in case this one ever catches you out....
Cruising along in my EL I6 Auto at about 100k's and the auto suddenly jumps back to 2nd cog - then hunts between 3rd and 4th with lots of slipping in between. I pull over and then notice it wont idle at all - has the staggers and is running way over rich (black smoke). Then on a restart it settles but now we have only 1st through to 3rd cog with no lock-up, it is shifting based on speed and not engine load, and the shifts are as firm as can be.
A later check of the fault codes reveals a Throttle Position Sensor (TPS) fault and an idle under / over fault. I checked the TPS for resistance against the manual and all appeared to be OK, but when backprobing the ECU and looking at the voltages the TPS signal was reading about 3V at idle where it should have been at 0.6 to 0.8V. Having measured the sensor and believing it to be OK I suspected a loom fault or ECU fault. Measuring resistance of the loom back to the sensor cleared it of suspicion and checking the voltages at the back of the TPS (Pin B and ground is the signal, pin A and C should be 5V) showed that the signal out of it was wrong.
I got a new one from Repco (Ford wasnt open) although it cost $150 supposedly at trade price. Ouch. This instantly cured it.
The other interesting thing is that I believe that it has been reading high for a while as the tranny has been flaring between cogs a fair bit (which I put down to a failing trans / S5 fault), and it has been using a heap of fuel. Changing the TPS has fixed both and of course when you think about what the ECU uses it for it all makes sense. Thing is, it took for it to be really crook before the ECU logged a code.
Check the voltages before you go replacing it but if you are having fuel consumption or weird gearbox problems this could also be a culprit.