Throttle Position Sensor Wiring Question (A/T to M/T swapped)

nogard · May 19, 2014

I think I have it figured out, but hopefully a wiring guru will chime in (ehmm....Charlie?

)

Last fall I posted about a CEL and a few codes. Charlie brought up the point of the A/T car originally having a 3 wire TPS and the M/T car having a 4 wire TPS. I'm finally in the process of getting everything I want/need off the M/T donor car and sending it to Camry Heaven :lol:. The 4 wire TPS was on that list. I took the whole throttle body and cut the car side of the TPS harness.

Wiring wise this was the one thing I overlooked on the A/T to M/T swap.

I was just looking at the 1990 Toyota Camry Electrical Wiring Diagram FSM. It looks like the A/T and M/T TPS are also pinned out differently. I'm looking at page 55 all wires going to the TCCS ECU. If I'm reading correctly all the "S" circled pins are for the A/T that say W/ ECT? Then all the "T" circled pins are for the M/T that say W/O ECT?

It looks like the potentiometer has the fixed resistor left open on one end for the A/T use. For the M/T both ends of the fixed resistor of the pot are wired in.

A/T wiring as follows:

Pin 1 - Blue - IDL
Pin 2 - Brown - E2
Pin 3 - Black/Red - VTA

M/T wiring as follows:

Pin 3 - Blue - IDL
Pin 4 - Brown - E2
Pin 2 - Black/Red - PSW (VTA)
Pin 1 - Blue/Red - VC (additional wire)

Can just the TPS be swapped onto the throttle body, or does the whole throttle body have to be changed?

If I cut the car side of the TPS wire harness I should be able to wire color for color the 4 wire TPS harness/plug for the M/T donor car into the original A/T car wire harness, correct?

If so then the only wire I need to tap into is the Blue/Red that goes to pin 1 and the VC pin of the TCCS ECU. Any ideas for a point that I can neatly tap into? I see the air flow meter harness has the Blue/Red - VC wire in it.

I also take it I don't have to worry about the Black/Red wire that goes to the TCCS ECU, VTA (automatic) or PSW (manual) pins, since I swapped my ECUs. I also looked at my spread sheet I made of both the 1988 Manual and 1990 Auto TCCS ECU pin outs. Both have a VTA in the same pin position! Neither has a PSW.

white90dx · May 19, 2014

Swap your ECU back. Leave the wiring alone. :thumbsup:

-Charlie

nogard · May 19, 2014

Charlie, can you elaborate a little?

Doctor J said:
This is cool topic I tried figure it out to for professional prestige J
The MT and A/T cars without ECT (a140L transaxle use same 3 wire switch type TPS)
So if you are installing M/T in non-ect car (like Atobe did) no wiring work is needed
The 3-wire TPS has 3 outputs:
Grounded idle wire from ECU --- throttle closed
No connection made (engine is off-idle)
Grounded (PWR) power wire --- “pedal to the metal”
But if you are installing M/T in ect car with 4 wire teardrop sensor the following work is needed:
Unplugging (and optional removal) of ECT control unit located on the dashboard reinforcement beam above glove box) to kill the o/d off flashing light
Most likely ECU swap (need to double check this out)
Swap of the sensor (it looks like same throttle body accepts both sensor types at least on 88 year model)
Installation of the 3-wire sensor connector with 4 inches long wire pigtails

This diagram has an error and shows 3-pin sensor as the one W/ECT!!!
I am pretty sure about that because I have been working on B0TH cars J

To splice TPS sensor connector:
1. Cut the old connector
2. Connect brown wire (green arrow) to the wire coming out from center cavity (it should be brown as well)
3. Connect light blue wire [IDLE] from harness (red arrow) to the wire coming from cavity #1
4. Connect Black wire with Red tracer from harness to the wire coming from cavity #3
Adjust the sensor and check the engine operation
Solder wires together and insulate them with 1/8” shrink wrap

I did have a A140E with the ECT on my 1990. The 1988 donor was S51. I didn't get a chance to study the TPSs yet, but I did think it was odd they way it was show in the wiring diagram. I also thought last fall Charlie said the A/T has 4 wires and M/T has 3 wires. That is not what the FSM diagram shows, I'm looking at the same one you posted.

I did unplug my ECT and removed it. I get the concept about swapping TPSs and rewiring, but what is the difference between the ECUs?

So what is the verdict, I'm getting mixed signals from two gurus :rofl:!

Doctor J · May 19, 2014

This is cool topic I tried figure it out to for professional prestige J
The MT and A/T cars without ECT (a140L transaxle use same 3 wire switch type TPS)
So if you are installing M/T in non-ect car (like Atobe did) no wiring work is needed
The 3-wire TPS has 3 outputs:
Grounded idle wire from ECU --- throttle closed
No connection made (engine is off-idle)
Grounded (PWR) power wire --- “pedal to the metal”
But if you are installing M/T in ect car with 4 wire teardrop sensor the following work is needed:
Unplugging (and optional removal) of ECT control unit located on the dashboard reinforcement beam above glove box) to kill the o/d off flashing light
Most likely ECU swap (need to double check this out)
Swap of the sensor (it looks like same throttle body accepts both sensor types at least on 88 year model)
Installation of the 3-wire sensor connector with 4 inches long wire pigtails

This diagram has an error and shows 3-pin sensor as the one W/ECT!!!
I am pretty sure about that because I have been working on B0TH cars J

To splice TPS sensor connector:
1. Cut the old connector
2. Connect brown wire (green arrow) to the wire coming out from center cavity (it should be brown as well)
3. Connect light blue wire [IDLE] from harness (red arrow) to the wire coming from cavity #1
4. Connect Black wire with Red tracer from harness to the wire coming from cavity #3
Adjust the sensor and check the engine operation
Solder wires together and insulate them with 1/8” shrink wrap

dem2757 · May 20, 2014

did jet speed have an issue with fuel cut deceleration getting a fuel dump at around 1k due to the missing torque converter with an AT ecu?

mcx · May 20, 2014

my 91 with auto/ ECT is a four wire TPS..that factory chart is incorrect.

white90dx · May 20, 2014

There were minor wiring changes through the years (the diagram for the '90 that I have won't show the fuel injector ballast resistor, for example. It also doesn't show the correct under-dash connectors for my '89 Alltrac). I can confirm that the auto and manual trans TPS's were different on the earlier years. There may be (almost certainly are) differences in fueling, etc. between the manual trans and auto trans ECUs, especially near idle - but it shouldn't cause any major drivability issues.

-Charlie

Doctor J · May 20, 2014

On CA cars 88’ ECU will not detect EGR temperature as well as operation of secondary oxygen sensor, which were added @1989.

nogard · May 22, 2014

I had a chance to check what was on the 1988 M/T donor, it is the 3 wire. 1990 that had A/T w/ECT is still in storage, didn't check yet, but will later.

Is there any damage that can be done if I leave the TPS the way it is, 4 wire in the 1990 that had A/T and swap the original ECU back in as Charlie suggested?

Otherwise I am prepared to swap TPS, 4 wire to 3 wire. Knowing how it is really wired and that the FSM wire diagram is wrong makes it easier to go from 4 to 3 wires

.

Throttle Position Sensor Wiring Question (A/T to M/T swapped)

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