TPS adjustment

[93 Z32]

I bought a new voltmeter just for the TPS adjustment.

I've read forums that just confuse me.
First, do I start the car? I read u need to open the throttle wide open, don't think I wanna do that with it in park.
Or do I just turn the key over so that power curculates thru the car but doesn't start?
Then, which plug do I slip the paperclip in? (I bought small thin paperclips for this) Is it the plug that plugs into the actual body of the TPS? Or the gray plug that goes to the engine harness?
And which wire located on the plug do I insert the paperclip in to make contact?

I'd appreciate anyone's advice and direction on this.
I do know once it's set, to unplug the gray plug for 10-20 seconds so the ecu resets as I had to do that when I replaced it. It's a brand new TPS.

[GerryO]

The TPS is a variable resistor and one of several inputs to the ECM that contribute to controlling the idle speed, engine and automatic transmission functions, such as shift points and OD lock-up.

Setting the TPS output voltage is a matter of fully warming up the engine, but first making sure that the throttle bodies are clean, so that they always close fully, meaning that the TPS always returns to the same position physically, whenever the throttle is fully released. Throttle fully CLOSED and not full open, and engine idle speed is lowest with the transmission in Drive and fully stopped with your foot on the brake.

The TPS output voltage is set with the engine running and a new reference setting is stored in the ECM by momentarilly disconnecting and reconnecting the TPS connector with the engine running. It will stumble a bit and the engine won't start with the TPS disconnected.

I'd use a strand of copper wire, as the contact resistance of copper wire will be lower than that of a galvanized or chrome plated iron paper clip. Note the strand of copper wire protruding from beneath the white wire in the photo below.

[93 Z32]

So I need to do it with te engine running?

[93 Z32]

Had it set with paperclip at .45
When I put in copper wire, it read .46

So I adjusted it back down to .45

[GerryO]

Sounds good. What's the fully warmed up, transmission in Drive, fully stopped with your foot on the brake pedal, with no AC or load on the alternator and PS (wheels pointed straight ahead), engine rpm speed at idle? My TPS output voltage is set to 0.38 VDC and the engine idles at about 650 rpm under the conditions listed above.

[93 Z32]

I'm a rookie with the electronics lol. She idles right at about 700rpm with foot on brake in drive. But I've noticed that when I'm driving, it takes it awhile to shift into the next gear. Throttle is more responsive but it's like it wants to wind out the gear then shift hard. Where as before, it would just shift nice and smooth. Think I need to lower it down closer to .40? I don't wanna burn up my trans but letting the rpm ride high before it shifts.

[93 Z32]

What does 'VDC' mean?

[93 Z32]

Guess I'll take the day tomorrow and fine tune it. Adjust it a lil, take it for a ride. Let it run thru the gears and see how it feels. Keep doing that till I find the sweet spot.
All the Z32 technicals that I found, said to set the TPS at .45. But it just doesn't feel right. When I replaced the TPS, then hooked it up, it read .32. That didn't feel right either. Felt a lil sluggish. And of course being an automatic, it's a dog off the line, but I think I need to lower it somewhere between .37-.42

[93 Z32]

I actually had to do the wd40 lube on the iacv. Then I adjusted my idle down. It was idling up around 1050-1100 rpm. But I adjusted the TPS to .45 before I adjusted the idle down. Now when I start it(cold start), it goes up to about 1300rpm for a couple seconds, then drops down to 800-850. Then put it in drive, goes down to about 650rpm like u said. But it just wants to whine the gear out then shift, and shift kinda hard. So I should probably lower the TPS voltage huh?

[GerryO]

What does 'VDC' mean?

VDC, voltage, direct current

VAC, voltage, alternating current

[GerryO]

I actually had to do the wd40 lube on the iacv. Then I adjusted my idle down. It was idling up around 1050-1100 rpm. But I adjusted the TPS to .45 before I adjusted the idle down. Now when I start it(cold start), it goes up to about 1300rpm for a couple seconds, then drops down to 800-850. Then put it in drive, goes down to about 650rpm like u said. But it just wants to whine the gear out then shift, and shift kinda hard. So I should probably lower the TPS voltage huh?

Lowering the TPS voltage will lower the idle speed, and make those shifts happen earlier and more smoothly. Go too far and the transmission will "hunt" between 3rd gear and OD, when pressure on the gas pedal is light. Idle speed can be increased by adjusting the idle screw on the side of the IACV.

[93 Z32]

So I need to lower the voltage on the TPS. Which will lower my idle speed. So then I need to adjust the iacv back up a lil to compensate for the voltage drop.
So I need to find that sweet spot. I did notice that when I raised the voltage from the .32 it was set at, the throttle is more responsive. But shift points are bad. Ill drop it down to about .35 and adjust up from there. Thank god I live out in the sticks in southern Louisiana so I can get on the road and test it easily lol.

[93 Z32]

So this would explain my poor fuel mileage too then?
Car is maintained very well. New injectors. Plenum/fuel rail insulators. Plugs. Coil packs. Fuel pressure regulator. Fuel filter. TPS. PTU. PTU sub harness. New vacuum lines. Pcv hoses. Order all parts thru Z1.

[GerryO]

So I need to lower the voltage on the TPS. Which will lower my idle speed. So then I need to adjust the iacv back up a lil to compensate for the voltage drop.
So I need to find that sweet spot. I did notice that when I raised the voltage from the .32 it was set at, the throttle is more responsive. But shift points are bad. Ill drop it down to about .35 and adjust up from there. Thank god I live out in the sticks in southern Louisiana so I can get on the road and test it easily lol.

I tried, very unsuccessfully, to adjust mine by feel and focusing primarily on idle speed, without using a meter to measure the output voltage. Another thing to watch closely is engine rpm speed at highway/cruising speeds when in OD, as it really effects gas mileage. My J30 runs about 2,800 rpms at 70 mph.

There is a lot of transmission info in this pdf, if you can get it to download.

http://www.240edge.com/manuals/89-90_240sx/auto_tra.pdf

http://www.pdfbeast.com/auto-trans-diag ... 314215099/

[93 Z32]

Man that's like reading Chinese. Lol. Looks like I have a long day ahead of me tomorrow. If I can't work it out, I'll take it to an import shop. Or dealership. Have to go there and pick up some extra gasket anyways. But I'll do some trial & error tomorrow

[GerryO]

So this would explain my poor fuel mileage too then?
Car is maintained very well. New injectors. Plenum/fuel rail insulators. Plugs. Coil packs. Fuel pressure regulator. Fuel filter. TPS. PTU. PTU sub harness. New vacuum lines. Pcv hoses. Order all parts thru Z1.

A couple of new O2 sensors improved my fuel mileage. I also replaced PCV valves and made sure that the IACV, AAC and Air Regulator were working properly and clean. I also unclogged the EGR tubes, when I pulled the plenum.

http://www.mdsmarthome.com/z/Z%20Tech/Z ... 20Idle.pdf

Have you checked ECM codes? A bad knock sensor, a Code 34, doesn't cause the CEL to turn ON, and really affects performance and fuel mileage.

[93 Z32]

What's the 'CEL'? Still haven't figured out how to pull codes yet. Had the car about 10 months. Just been replacing things here and there. Guy I bought it from neglected it. I was getting great fuel mileage when it was set at .32.

[93 Z32]

Oh check engine light. Gotcha. I've actually had my car hooked up on the diagnosis machine at Nissan twice. And the only thing that came back was a bad injector. Which I replaced last weekend.

[93 Z32]

I just found a write up on pulling codes. I'll have to do that. But I think I'm gonna drop it back down to where it was at .32. Then work my way from there. I'll take it .01 at a time and adjust the iacv accordingly. Might cost me 100 miles on the car to get it worked out. Lol. If I can't get it straight, I'll run it over to the dealership so they can beat me over the head $129hr labor lol

[93 Z32]

I just can't see how all the technical write ups I've seen on setting the TPS, say to set it at .45. Cause obviously that's way too high.
I'll get it worked out tomorrow tho

[93 Z32]

Question, how do u post pics on here? I'm using my iPhone. My laptop crashed, so I fixed it with my hammer. Lol. iPhone is all I have now

[93 Z32]

So basically TPS setting are virtually different for each vehicle? Hope I'm not irritating u with these questions. I chased this car for many years. And like a female, it's inner workings are very complicated and complex. I've done LOTS of research on my car. But research alone doesn't help one to diagnos and fix issues. If that were the case, I'd be a genius with this car. I can't really do any major work on the car myself cause I fell 32' 2 years ago an broke my back and neck. And still have major complications with both. So my cousin does all the hands on heavy work for me. And the only performance upgrade is the exhaust. Factory was shot. So I upgraded to megan racing type2 catback and downpipes. But I've spent a total of $2,602 after the initial purchase. It does have the 1 piece driveshaft from Z1. New transmission mount. Replaced the windshield. And many other things. I'm not looking to beat some teenage road racer. As I'm 33. I just want to have a vehicle that runs to its top potential.

[93 Z32]

Set mine at .39. Took it for about a 20 minute drive, fuel needle didn't even move. Shifts beautifully. I had my voltmeter on the wrong setting. So it was set in the .5s. Way to high. I greatly appreciate ur help and knowledge.

[GerryO]

Set mine at .39. Took it for about a 20 minute drive, fuel needle didn't even move. Shifts beautifully. I had my voltmeter on the wrong setting. So it was set in the .5s. Way to high. I greatly appreciate ur help and knowledge.

Glad to read that things are improving, and thank you so much for the updates and the thank you.

Got over my fears of working on the VG30DE engine, while unemployed several years ago. Everything fits so precisely and has a specific purpose, plus so many things can be tested individually, and simply cleaned up and adjusted to improve performance.

Believe manual transmission cars also have a TPS and suspect its' output voltage doesn't affect how as many other pieces of equipment function. Hope your cousin is careful with your O2 sensors and replacing the passenger side was the tougher of the two on my J30.

[93 Z32]

I may just have the shop do the O2 sensors in a couple weeks when I have the 120,000 mile maintenance tune done. Only thing I don't like about the Z32 series, so many different parts that overlap each other. And u can't get to anything around the back of the motor unless u do a pull. Or just tear it down. So far I've had good luck with this car. And once I get te maintenance tune, should run even smoother. Taking it to a shop that works on nothing but Japanese cars. And they are very knowledgable about this particular motor

[93 Z32]

How hard it is to change out the O2 sensors? I'm gonna order them tomorrow. My buddy has a lift at his office. So it won't be that hard to get underneath the car. I have Megan racing type2 catback system and down pipes. Will I need to remove the downpipes to access them? I have a whole nother complete set of gaskets for the flanges for the exhaust. So that's not an issue.

[GerryO]

How hard it is to change out the O2 sensors? I'm gonna order them tomorrow. My buddy has a lift at his office. So it won't be that hard to get underneath the car. I have Megan racing type2 catback system and down pipes. Will I need to remove the downpipes to access them? I have a whole nother complete set of gaskets for the flanges for the exhaust. So that's not an issue.

It's been a few years since I did mine. It's important to have the proper O2 sensor socket, breaker-bar and open-end wrenches, and it probably helps to apply some penetrating oil first, giving it ample time to work its' way in. The O2 sensor on the J30 passenger side threads into a threaded reducer bushing that came out along with the sensor. Separating the two galled the inside threads of the reducer bushing, but I was able to use the other old/good O2 sensor, along with some lubricant, to chase and clean them up. No project ever goes as smoothly as it should.

I bought a pair with connectors already attached and used the supplied copper anti-seize when installing them. You might do some searching on-line for a write-up. Let us know how things work out.

[93 Z32]

Definitely will. When it comes to operational/performance affecting parts, I only order from Z1. I have the socket already, as I've had to change them on several other of my vehicles, including 90' 240sx. I'll get everything required for installation from Z1. I have penetrating oil and antiseize. I buy that in bulk lol. Buddy has a lift, so I think we're just gonna put it in the air, remove the downpipes and go from there. I researched a lot last night, just gotta have a lil patience when it comes to replacing 19 year old parts.