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Discussion Starter · #1 ·
My throttle position sensor is no longer getting power, and I cant find a fuse or relay for it? Does it even have a fuse/relay? Or would it be one for the ECU? I checked both the main fuse box under the hood and the one inside car under the steering wheel, and all the fuses are good. And if the ECU relay was bad, wouldn't there be a lot more components not working??
I dont have much experience with this, it's my first project car, and I'm stuck.

I followed the wires to the wire harness and followed until it goes into the firewall behind the glove box. I removed glovebox and now I think I might have figured out which wires they are, going into the ECU box, but I'm not sure what to do now.. If anyone can point me in the right direction, I'd super appreciate it!
 

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Drivers foot (left) side fuse panel there's a power relay there (at least for a 85/86), use a large paper clip to insert to reset
 

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There's a jumper E1 connector on the engine harness under the dash on the later cars that supplies part of the circuit
 

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Discussion Starter · #4 ·
SilverMK2, is that one of the yellow convectors going into the ecu box? And so what am I supposed to do? i check each wire to see if they all have power while the engine is running or just while the key is turned in ignition?

AJ, is the relay round with a flat top? And is the hole in the top of the relay? If so, I think I found it, but it didnt feel like I hit a reset button or anything when I stuck the paper clip in..
 

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Yes, make sure its plugged in. At least in 85 E1 pin 9 feeds 5 V from the X connector on the ECU to the TPS and water temp sensor. There are a few other things on that connector like cruise control and water temp gauge.
 

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Your not saying if the car runs or just cranks. The TPS wires go directly to ECU. So try the following.

When you tested for no power with ignition on with TPS disconnected and center pin (red wire) showed no battery voltage on harness , then check at ECU pin 4 large connector. If no power then check 15a EFI fuse its ECU power source. Check 7.5a IGN fuse also.
 

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Discussion Starter · #7 ·
82TURBOSUPRA, so I just got the car running a few months ago, and it was driving pretty smooth for a while. Now if I try to drive it, each time I shift to a higher gear the tachometer fluctuates up and down as the car jerks back and forth. It seems to go away once I ease up on the throttle until I'm just very lightly pressing on it. While I was trying to narrow down the possible causes I noticed the TPS connector wasn't receiving any power. I only have the general TSRM for 79-92 and was super confused with the wiring diagram..
Only just last night I found an 82 specific EFI wiring diagram and it's starting to make sense. And your instructions just simplified it way more, thank you! I'll post again soon with my results.
The only other thing I'm having trouble finding in these diagrams is which ground point does the TPS/ECU connect to? Or is it the EFI fuse the ground point?
 

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Ground for 82 TPS is at the ecu. You can test voltage back probing pins 4, 5 and 6 to pin 8 (white/ black stripe) or a good ground point. Need to move throttle to test for open. If voltages are not there open ECU and check for bad solder joints for those pins to board and any burnt resistors and replace. 82 TPS wiring not the same as 83 to ecu. You might have to adjust the TPS once power is corrected.
 

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Discussion Starter · #9 ·
So when I tested all of the pins on the connector to the ECU, the only 2 wires that had power were the 2 ground wires? IIRC pins 7& 8, the two White w/ black stripes. Shouldn't those ground wires only have power if the rest of the wires on the connector have power?

So now I should open the ECU and check for bad solder joints/ burnt resistors? Or could there be another problem now?

For a brief period before this all started, when I pressed on the brakes, the whole car would shut off like it wasnt even connected to the battery. I can still hear a relay click occasionally if I press the brake or turn the wheel. So I was thinking maybe a wire near the brakes or something might be crossed or cut and shorting out the system? What do you think?
 

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The electrical system is marginal on these cars. 4 stop lights is enough to create a load on the system. When troubleshooting power issues, it's always good idea to wire a DVM on the battery to monitor voltage at the source. The relay clicking could be caused by voltage lowering and not enough to keep them on.
 
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So when I tested all of the pins on the connector to the ECU, the only 2 wires that had power were the 2 ground wires? IIRC pins 7& 8, the two White w/ black stripes. Shouldn't those ground wires only have power if the rest of the wires on the connector have power?

The ground wires for pins 7 and 8 start under the intake manifold ground bolt and go to the ecu.
To test: ignition switch to on position and TPS must be plugged in.

Pin 6 to pin 8 voltage 8-13 throttle valve closed.
Pin 5 to pin 8 voltage 8-13 throttle valve open.
Pin 4 to pin 8 voltage 8-13 always.

Like RedP85 said about the voltage drop, most 12v relays won't stay energized after 8 to 9 volts.
Is your alternator working correctly, does this only happen when headlights and blower fan is on or rear defroster.
Take lower cover off and check for any wires interfering with the mechanical brake linkage.
Buy a plug in volt gauge .
16322
 

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Discussion Starter · #12 ·
So I just checked with a voltmeter and it read ~7 for pin 4 to pin 8 and pin 6 to pin 8, and ~18-19 pin 5 to pin 8. But neither 4, 5, or 6 will power my test light? Should the test light light up or does that not matter?
I'll get a DVM by this weekend to connect to the battery and check everything again. The alternator seems like it's been working fine the whole time I've had the car, but I'll try to check it tomorrow and make sure. And no, unfortunately this always happens--no air blowing, no headlights on. It jerks super bad as I accelerate through each gear, but once I ease up on the gas pedal and keep just a small amount of pressure on it to keep my speed consistent, it stops jerking and the Tach stops fluctuating& levels out, and it drives fine...
 

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Discussion Starter · #16 ·
Okay so I found out I was wrong about what is causing the problem, and the TPS is actually fine. The pins on the ECU all read in the correct range, the connector works, and the resistance on the TPS was in the correct range as well. So I will make a new post for further help with the matter.

Thank you all so much for your help with this! I had no clue what to do or where to start before, but it's starting to make sense now.
 
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