AEM EMS Variable TPS How To!
 

After reading another variable TPS how to, I figured I'd throw up my experience with a different TPS on my 1.6L miata. I used a new Beck/Arnley TPS from a 1991 Nissan 240sx (5spd). I chose this because they are quite cheap, are super easy to find used, and they have a cable coming off of them, so it's very easy to wire it into the stock harness. Here is what the new tps looks like:

http://www.dbmiata.com/miata/tps/tps2.jpg
Like the stock wiring, it is a 3 wire setup. The black wire is ground, Red wire is power, and white wire is the signal. On your miata, you will have to move the TPS wire on the ECU from 2L to 2W. Here is a picture of the wiring harness:
http://www.dbmiata.com/ecu.jpg

So, here's the basic how to:

Things you will definitely need:
- Two small self tapping screws
- A Marker
- Double Sided Tape
- Some pliers and a vice (or a hacksaw)
- A Drill and a holesaw (or something to cut metal)


Step 1 - remove the stock tps and take it apart. Remove the plastic cover, and all of the little metal arms. You'll be left with the metal base, and the spinning part in the center of the base. The stock TPS looks like this:

http://www.dbmiata.com/miata/tps/tps.jpg

Step 2 - it will help dramatically to have a drill press and a hole saw, but you could do this several different ways. I used a hole saw and cut the center right out of the metal base:
http://www.dbmiata.com/miata/tps/SSPX0255.jpg

Step 3 - With the hole enlarged in the middle, I then went and straightened the metal base out (it has an L bend in it). I just used a vice and some pliers to get it reasonably straight:
http://www.dbmiata.com/miata/tps/SSPX0257.jpg

Step 4 - put the base back on your throttle body, and screw it in. Then, get some double sided tape and put it on the new Nissan TPS. Put the new TPS onto the throttle body, and hold it in your hand while moving the throttle. Make sure there is enough room for the throttle arm to rotate completely. I found that having the Nissan TPS line up exactly with the original plate worked fine for me. Once you've verified that the throttle can move properly, push the new TPS onto the old plate so that it sticks. Unscrew the original plate and pull the two off.

Step 5 - Using a small drill bit (smaller then the self tapping screws), drill two holes (one on either side of the TPS) that go through the baseplate (you can use a marker if you want - not super neccesary, just make sure they're centered). Once the holes are drilled, screw the sell tapping screws through the Nissan TPS metal arms and into the base plate (all the way). Once they are tightened, use a hacksaw or some cutting device to cut the backs of the screws that are piercing through the original TPS plate.

Step 6 - Install your new TPS! Push it onto the throttle rod, and use the original screws to mount it.

Step 7 - Wire it up! It's pretty straight forward. The easiest way is to cut the end of the factory harness for both the miata and the Nissan TPS, and then solder / connect the wires together. Make sure you also get access to your ECU and move the tps signal wire from 2L to 2W. Your AEM EMS will have come with extra ECU pins, and they fit the stock miata harness.

Here's a pic of mine installed (please ignore the hole in the top of my TPS - long story):
http://www.dbmiata.com/miata/tps/IMG_3725.jpg

***** SOFTWARE STEPS *****
Step 8 - Open your AEM Pro software and connect to the ECU. Go into Setup -> Sensor -> Throttle Position Sensor -> Options. Change the Throttle Analogue Input to TPS Voltage.

Step 9 - This Nissan TPS rotates the opposite direction of the miata, so you need to invert the voltage settings. Go Options -> Full List. Scroll down to TP RAW INVERT. Change the setting to ON.

Step 10 - Go to Idle -> Advanced Idle -> Idle Switch Input. Make sure under theadvanced idle table you have "Idle Switch Input" set to "Switch is Always OFF"

Step 11 - Go to Configure -> ECU Setup -> Set Throttle Range. Follow the onscreen steps to calibrate your TPS.

Congrats, you have a variable TPS! My car ran 100 times better with a variable. It used to be very jumpy when going on or off throttle, and is much smoother now. I hope this helps you!

Here's information you might need on finding one of these tps's:

The Beck/Arnley part number is 1580490.
Here's the application list for the TPS (must be manual transmission):
NISSAN 240SX (1991 - 1995)
NISSAN 240SX LE (1991 - 1992)
NISSAN 240SX SE (1991 - 1995)
NISSAN ALTIMA 1993
NISSAN ALTIMA GLE (1993 - 1995)
NISSAN ALTIMA GXE (1993 - 1995)
NISSAN ALTIMA SE (1993 - 1995)
NISSAN ALTIMA XE (1993 - 1995)

great write-up!

Your guide is missing a very important step 12:

Go to the TPS setup and manually alter tha values so you never get 0% or 100% throttle reading. Adjust the numbers so you're around 1%-2% with the throttle pedal released and around 98% at WOT.

This is MANDATORY. You should never ever see 0% throttle in the software or otherwise it won't work correct.

Just realized I made an error in wiring. Move wire from 2L to 2M, not 2W.

I am a moron for missing this all this time. I'm blaming it on my annoying little kids.

Should be a sticky.

I guess I have an update. I installed one of these on a friends 92 miata, and I just made my own bracket out of flatbar. I just drilled a hole large enough in the center, and used two sheet metal screws to attach the TPS to the bar (shaved off the rear like I did with the other one). Looks much cleaner, and worked great. I'll try and get a pic up.

And I'm glad a few people are using this :)

Pretty slick.

All you had to do is buy a throttle body withy the 4 wire TPS from a Mazda Protege automatic, must be 1.8 DOHC engine to have the bigger bore.

If you decide to grab the TB from the 1.8 SOHC, it will be much narrower on the TB plate (token WE U want to call it)...

this writeup is fantastic. i did it tonight and my car runs, and idles 100% better now.

Would this still work if I'm running a F/IC instead of a EMS?

i made mine way easier than this looking back....


i just cut the bottom of the miata one off and made it flat, bolted it to the throttle, put the tps on and tack welded the nissan tps to the miata baseplate.

Agreed, it can be done way easier since I first did it :) I just got a piece of flat bar, drilled a hole in the middle, bolted it onto the throttle body, and then attached the Nissan TPS to the flatbar.

Well I would think the AEM f/IC would read the variable tps, but it's just a piggy back so the stock ECU wouldn't be getting any proper signals as to the car being in WOT, etc.

So then how would i get the TPS wired up on the F/IC? Should get a TPS from an automatic miata or just wire the F/IC into 2L?

Sorry to bring this back from the dead. Looking at a wiring diagram, and comparing to what I saw while the harness was apart, while the black/lt green is ground, the red and ltgrn/white wires are both continuity inputs to the ECU. Neither of them are a 5V reference. I've read this over a couple times, but it didn't look like you changed the ECU anywhere to output a 5V reference on the 1N (closed throttle switch) pin. I was contemplating just slicing it out and merging it with the 2K line (the 5V ref out), but it sounds like you got around that somehow?

I stupidly recovered the whole harness before remembering to deal with the TPS wiring issue. I could tear it back apart and splice into the 5VRef down there too, which is also an option. I'm just wondering if there's an easier way.

It's been a while since I've even thought about this, and I realize now that in the write up I didn't actually specify what wires to hook up. One of the wires is indeed a variable voltage line, I just can't remember which one.

Interesting. On the stock ECU they're definitely both inputs. I haven't actually gotten the AEM in the car yet and even looked at the settings for the EMS (never used an AEM before, only Nemesis, Autronic, and Megasquirt), so I don't know what's available. In theory, it sounds like, you can enable one of those lines to be a reference voltage line?

TPS Settings Help!!
 

So I got the tps in wired it up but my Aem Ems4 won't let me play with the TPS settings it's almost as if they were locked in? I'm trying to change the following Step 9 - This Nissan TPS rotates the opposite direction of the miata, so you need to invert the voltage settings. Go Options -> Full List. Scroll down to TP RAW INVERT. Change the setting to ON.

Step 10 - Go to Idle -> Advanced Idle -> Idle Switch Input. Make sure under theadvanced idle table you have "Idle Switch Input" set to "Switch is Always OFF"

Step 11 - Go to Configure -> ECU Setup -> Set Throttle Range. Follow the onscreen steps to calibrate your TPS.
But everytime I try doing step 9 the invert goes back to off like if the option was locked in some how?
Any help or anything I'm doing wrong or missing? Thanks!

After you change the settings, you mist hit ENTER on your keyboard. If you just use your mouse to change it the settings don't stay.

will this work for megasquirt pnp2