mx5cartalk.com

Hi all,

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!

I can confirm that this is all 100% accurate.

Excellent writeup.

Dann

+ 1

Great write up, with great photos

Just thought I would ask

Without an MS, would this work/have any benefits with the stock ecu?

Slightly off topic, but my car had a VTPS installed with megasquirt and my tuner can't get it to work for some reason. So right now boost is just set relative to RPM instead of TP.

Is it possible for someone who knows that they are doing to get it to work, or must it be done on the dyno? I just don't want to do anything that would affect the tune.

MosieurCinq wrote:Without an MS, would this work/have any benefits with the stock ecu?

Probably not, the stock ECU only knows what the stock sensors tell it.


I only speak english, and I have a great book at home on the basics of engines.
I could get a more detailed book easily, but if the additional detail is all in chinese I won't get any benefit from it.


Same idea with the factory ECU, a variable sensor might be giving it better info, but the ECU will likely jsut ignore it because it's not been taught how to understand that language so to speak.

hks_kansei wrote:
I only speak english, and I have a great book at home on the basics of engines.
I could get a more detailed book easily, but if the additional detail is all in chinese I won't get any benefit from it.

Haha, noted! I'll leave it for my turbo install then

Awesome parts sourcing and write-up mate!

Nice man! I did a similar thing but modified the TPS so it would plug into the stock loom. Details can be found here:
https://plus.google.com/u/0/photos/1168 ... 2233581457

WARNING!!!! super thread revival!

VL commies are a bit thin on the ground now in NZ....does anyone know if the nissan RB20 RB25 from a R32 skyline/laurel fits with the above mods??

Hmmm. Not sure about the RB option, but the BMW e30 has a relatively compatible unit iirc.

I suspect that most Nippon Denso units will be close, especially anything from early to mid 90s cars

thanks. the e30 bmw ones are EXPENSIVE in NZ... wreckers want stupid money for them and most ebay ads a re a bit vague on exactly which model they are selling(theres two types, a VTPS and non VTPS)

My itbs use a the stock Toyota vtps from an ae101 Corolla. It's values read backwards to a mazda but not an issue for an aftermarket computer.

Factory mazda wiring plugged in but need two wire positions swapped (middle two for memory)

So maybe try some Corolla?


Sent from my iPhone using Tapatalk

I would also add.. don't be too hasty in giving up on map dot accel enrichment. i have no hesitation or lean spikes after installing a fuel filter in my MAP line using the stock NA tps.

It's more a refinement than necessity

Paulus wrote:I would also add.. don't be too hasty in giving up on map dot accel enrichment. i have no hesitation or lean spikes after installing a fuel filter in my MAP line using the stock NA tps.

It's more a refinement than necessity

Sure, but cl idle works best when it knows the position of the TPS - without it, the idle code in the ecu isn't going to function correctly. Obviously you can try to run the car without the idle valve being used to manage AC, electrical loads, power steering etc... but it won't be as good as the CL idle code to get right.