I'm in the process of Megasquirting my MX-5, and while researching VTPS solutions (the stock manual NA has only switch TPS, which is not ideal for a MS install), I stumbled across this post http://mx5cartalk.com/forum/viewtopic.php?f=55&t=57566&hilit=vl+commodore, which got me thinking. For the record I've got a early 1.6 manual NA. Auto transmission owners already have a VTPS, manuals do not.
The good bits:
- It's a linear VTPS
It fits the MX-5 throttle body (with a bit of modification)
It's cheap, and you can find them at pretty much any wreckers in Australia
So I trotted off down to my local wrecker to peruse their fine selection of "pre-loved" VL Commodores. In exchange for $16 and a bit of skin from my knuckles, I got my mitts on the following item;
Important things to note & do:
- The OEM unit is on the left for comparison.
Take a multimetre with you to the wreckers, and test the VTPS you pull off. You should get readings between 1k & 12k (ish). You want to measure this by probing the pins on the large connector.
When you pull it out, snip off about 10cm of cable from the cars loom. Don't just unplug the connector and walk away with the TPS. Having the pigtail will make it easier to wire in.
The TPS has two connectors, one for the non variable (ie idle, not idle or WOT and WOT) and one for the variable component. Helpfully, as the VL came with a Japanese motor, they used the same Nippon Denso type connector as the MX-5 already has. So you could bolt this into your car, and use it with your stock computer.
My installation procedure required me to remove the throttle body from the car. If this hasn't been done in a while, I recommend you get a new throttle body gasket handy, as mine got shredded during removal, and air leaks will make your Megasquirt tuning life difficult.
The $4 warranty sticker is optional, although it came in handy for me after my wreckers TPS died after 1 day
.Installing it into the car:
You need to do 3 things to get the VL TPS installed;
1) Cut down the throttle arm so that the TPS fits
2) Massage the body of the TPS to get it to fit propertly
3) Tap a thread in the preexisting holes of the throttle body
Cut down the arm of the throttle body:
The VL TPS isn't as "fat" as the OEM, so the protruding arm which goes into the TPS to actuate it is too long. Cutting it down is the easy fix, and I checked, the OEM unit will still work once it's been cut down (as long as you don't cut it too far).
I've pushed the TPS onto the arm as far as it will go - as you can see it's not flush with the throttle body, and can't be screwed in. I lopped about 8 - 10mm off to get it to fit fine, please use your discretion and measure twice, cut once.
Since you need to tap some holes, and you can't do that with the throttle body on the car, you might as well remove it BEFORE getting the hacksaw.
Lop off a bit, file the edges smooth, and BE CAREFUL not to get filings down the throat of the throttle body. If you do, clean them out.
Next, you want to break out the dremel and file back the body of the TPS to get it to sit flush. Only take out material from the middle of the TPS, and try not to take too much, as the two tabs hold the black cover on, and you don't want it falling off. Feel free to epoxy over the tabs to ensure the thing stays together.
Last task is to tap the pre-existing holes in the throttle body so that you can screw the TPS on. Here is an illustrative photo;
As you can see, some engineer decided that standardisation was a Good Thing, and so there are some existing holes that we can use to mount the smaller VL TPS. Note that the holes have no thread, so you need to tap them. BE CAREFUL with this bit, you can a) bugger your TB or b) bugger your TB. Either way, you're not going to be a happy camper.
I didn't have a tap that was the same thread as the OEM screws, so I drilled out the holes a tad, and used the smallest tap I had. The TB is aluminium, which means it's soft, and if you aren't careful with your tap, you will not create a good thread.
Now bolt it up, and get the whole thing back into the car.
Wiring?:
If you're going down the Megasquirt path, you should know how to wire this thing in, and how to calibrate it. Either way, I cut off the OEM plug, then spliced in the wires of the large grey VL TPS plug (you did take a pig tail from the wreckers didn't you?) into the OEM loom. This way if I ever go back to stock, I can bolt up the old TPS. If you go down this path, DON'T plug in both connectors, as depending on how you wired them, your MS might not get a correct reading.
Calibrate your TPS (follow MS documentation), and then ensure that your accel enrichment is set for TPSdot. Drink beer and be happy.
That's it!
