Throttle Position Sensor Issue

[Kingman]

I got my '84 Z31-powered '88 Pathfinder up and running, and it runs like a raped ape except when cold and at idle. If I plug in the TPS (I've tried 4 others), it will idle smoothly but not rev above 2500. If I unplug it, it idles like ass at around 4-500 and sputters and pops and blows clouds of black smoke out the tail pipe but revs freely and responsively when warmed up, as well as the black soot clearing up once it's revved. From my understanding, pins 18 and 25 at the computer are for the TPS sensor, yet the wiring diagram I have labels it as the "throttle valve switch" and only measures idle, mid, and full throttle. The diagram I have only shows two wires coming from the sensor as blue/green and pink/blue, but says nothing about the third wire which is pink/black. Being it's got black on the wire, I assume it's a ground? This is a manual TPS sensor, manual computer, and manual truck. I've even ran the blue/green and pink/blue directly to the computer's pins and it still won't idle, but if I touch those two pins directly together with no sensor involved it'll instantly idle perfectly, just not rev. The Pathfinder TPS sensor has the 3 wires coming from the main body, and a secondary plug coming from the side. According to the diagrams, it's got a throttle valve switch and an actual throttle position sensor with a full-range potentiometer that go to different pins at the TBI computer. I would assume since the Z only has the 3-way switch those other wires shouldn't matter. Again, I've tried 4 different throttle sensors and they all do the same thing. I don't want to drive the truck much because running as rich as it is at idle is horrible for rings and such. Anyone know what specific wires need to be ran to the computer for the Z engine to run right? Any help is really appreciated.

 

I made a video of it, what hooking pins 18 and 25 directly together does is the same with hooking the TPS sensor up.

 

http://www.youtube.com/watch?v=BrvAravn6pM

 

And a video of the truck going, warmed up, wide open (for fun).

[hoov100]

Voltage should be .45-.52 at the TPS when closed. I don't know of the wiring is the same as a z32, but there should be three wires on a gray connector coming off the TPS, one should be carrying 5 volts when the ignition is on and the white wire in the center should be you need to measure. I would almost bet though, that you have a bad/wrong MAF.

[michaelp]

Voltage should be .45-.52 at the TPS when closed. I don't know of the wiring is the same as a z32, but there should be three wires on a gray connector coming off the TPS, one should be carrying 5 volts when the ignition is on and the white wire in the center should be you need to measure. I would almost bet though, that you have a bad/wrong MAF.

 

NO!. The Z31 does NOT work off 5-volt reference, in-fact you'll have 12-volts at the reference wire to the TPS. ALL the TPS is on the Z31 is an idle switch, and also a WOT switch on automatics (hence the 3 wires). On manual TPS', only 2 of the terminals/wires are actually used. 12-volt reference, and the "signal" wire for the idle switch to the ECU, which when the throttle is closed it has 12v sent to it.

[hoov100]

NO!. The Z31 does NOT work off 5-volt reference, in-fact you'll have 12-volts at the reference wire to the TPS. ALL the TPS is on the Z31 is an idle switch, and also a WOT switch on automatics (hence the 3 wires). On manual TPS', only 2 of the terminals/wires are actually used. 12-volt reference, and the "signal" wire for the idle switch to the ECU, which when the throttle is closed it has 12v sent to it.

 

 

If all I had one my 89T was the three wire TPS, then why has every 87T+ z31 I have owned had a 3 wire plug on the TPS body and have a separate 3 wire connector? very similar to 83+ nissan turbo cars?

[michaelp]

If all I had one my 89T was the three wire TPS, then why has every 87T+ z31 I have owned had a 3 wire plug on the TPS body and have a separate 3 wire connector? very similar to 83+ nissan turbo cars?

 

Because all you've owned were 86+ automatics, no manuals? The automatics had a separate 3-wire plug for a potentiometer, it controlled the transmission and thats all. Doesn't affect the way the engine functions at all, like my 88T which has only the one connector to the TPS and an idle switch...because its a man's car with a 5spd.

Edited October 24, 2010 by michaelp

[hoov100]

Because all you've owned were 86+ automatics, no manuals? The automatics had a separate 3-wire plug for a potentiometer, it controlled the transmission and thats all. Doesn't affect the way the engine functions at all, like my 88T which has only the one connector to the TPS and an idle switch...because its a man's car with a 5spd.

 

I've had two 5 speeds and one auto and they all had two connectors, the same as every 87T+ I have seen. Also the TPS is not a potentiometer..

Edited October 25, 2010 by hoov100

[michaelp]

I've had two 5 speeds and one auto and they all had two connectors, the same as every 87T+ I have seen. Also the TPS is not a potentiometer..

 

 

WOW man..WOW..really? You're just digging yourself into a big hole. The typical "TPS" Throttle Position Sensor, is a Potentiometer. It varies voltage throughout its sweep, its a variable resistor called a Potentiometer, utilizing 3 wires. The 3 typical terminals would be VREF (Voltage Reference), GRD (Ground), and SIG/SGN (SIGNAL).

 

The Z31 utilizes a single-connector TPS on manual cars, as throttle position SWITCH, and is only an idle switch. 86-89 Automatic cars have a secondary connector that has a potentiometer to show true throttle position for the transmission control module, while 84-85 are fully mechanical. ALL 86-89 cars have the connector in the engine wiring harness, but it does not do anything on manuals. The Automatic TPS has the secondary set wires on it with the connector, but the manual does not. The automatic TPS can be put on a manual car and it'll function perfectly everytime, you can even plug that connector in...but that connector isnt doing ANYTHING.

 

Source: 1989 300ZX FSM

 

Don't argue with stuff you don't know, and have just observed on your cars. I've made Z31 engine harness', I know where that connector goes, and its for nothing on the manual. If you get a chance to mess with nistune, you'll also notice it shows no throttle position on Z31 ECUs, but it will on Z32s. It shows "IDLESWITCH" as one of the possible faults.

 

http://xenonz31.com/reference.html