Bob_The_Normal

Well, having recently had my TPS go bad and had to replace it... and being the curious person that I am... I decided I wanted to know WTF was in my TPS and why it can't be rebuilt... why the hell do I have to pay $350 for a brand new one also? =/

After tearing it apart, I still don't have answers to those questions... but at least I know how it works. And that Mazda are ******** for charging so much. I bet they make a whole SHITLOAD of money off these stupid simple devices.

I would even expect that someone could MAKE these for cheaper, and rebuildable.

I didn't feel like hosting all the images I have for this tear-apart seperately so HERE (right click, save as) is a RAR pack with them. It's 7mb... yeah I could probably make it smaller... whatever. Just download it and un-rar it somewhere.

Ok this took me maybe 30 mins to do, but this writeup has kept me up all damn night and I'm too tired to finish it properly.

I started trying to be civil opening the TPS... pried the metal pins holding it onto the bracket off, as you can see in pics 24-26.

After that I attempted to open the thing up. This didn't work. It is SEALED shut, there is no way to open it.

What I eventually did was take a screw driver and a hammer... and I first broke off the back of it, where the wires were. This let me see inside, so I had a better idea of how to break it apart from there.

Also at this point a spring and a little metal bar came out. When I carried everything upstairs, these got lost. I don't know where they are... doesn't matter because I figured out how it works without them. Just know that although there are no pics, they were in there... and they fell out, so I wasn't sure where they went anyway.


Okay, so I split the rest of the TPS in half with the screwdriver/hammer.

You can see the main part of the TPS and generally get an idea of what the inside looks like from images 28-30.

Images 31-33 are a little black sliding piece with two fray-contacts... NOW, the REASON one of the fray contacts looks SHORTER than the other one in the pictures (sorry they're a little blurry) is because it IS. This is what failed in my TPS. One of the leads basically broke. They are very brittle, it was probably a bad combination of being old, really warm from where it is in the engine bay, and pressing the gas forward and backwards a little too roughly or something like that, that caused it to break. Which would mean the contact, although still sort of happening, was very frail and crappy... leading to weird resistance issues.

In image 34,35 you can see the top half of the TPS... it's just a block of plastic with a groove in it, that groove is for the top of the sliding piece.

37, 38 are to show what the whole thing would look like when it's together... so you can see what wires go to what leads on the resistance board. BTW that board, although I'm not very electrically inclined at all but I have taken basic classes and it's fairly obvious to me, is made of a semi-resistant material... just like resistors, except in printed circuit format. The more distance between two points on that material, the higher the resistance. Remember that because it's how this thing works.

Ok images 42-44 show how the sliding piece fits into the puzzle.

And 52 is just one last image, to show the whole thing... and the scratched up material on the right side of the picture on the resistance material... I'm ALSO guessing this had something to do with the failure... the scratch is fairly deep and took out a good amount of material.

OK!

So it's easy to see how this works now, but I'll lay it out.

I'm GUESSING at this, I want someone who knows what is really going on to support or slam my guess and tell me what's actually happening. If no one refutes it, I'd say I'm right. ;P

There are three leads, we have the

BLUE: (Picture 52) it connects to the lead on the RIGHT side of the picture. This lead is connected THROUGH the RM (Resistance Material) to the RED wire, and BY the SLIDING PIECE _and_ the RM to the LEFT / YELLOW wire.

I am guessing that BLUE is a POSITIVE wire, I would think it is charged... and it's purpose, I don't know. =/ I can guess, and say maybe the computer needs this as a starting point... the resistance between BLUE and RED will always be the resistance of 2 units of distance through the RM. Other than that, I don't know. Someone want to figure that one out?

It is always connected to the RED wire through the RM (2 units of distance through the RM is how far the current has to travel... what I mean by "units" is later)

RED: (Picture 52) it is in the middle. Again, this and the BLUE lead are connect (with or without the SLIDING PIECE) _THROUGH_ the RM. The distance between them through the RM is pretty far though. The green material is non-conductive.

I am guessing that RED is a NEGATIVE / GROUND wire... I think the current should flow TO this wire for the entire circuit. (Well, if you're using the conventional eletrical... yeah) The right lead on the SLIDING PIECE should be ABOUT 1 unit from this wire through the RM when the TPS is un-pressed.

YELLOW: (Picture 52) it isn't connected to anything. The SLIDING PIECE connects it to the other side of the circuit, where the scratched part is shows the path of the leads.

Again, I'm guessing that YELLOW is a POSITIVE wire and that it is charged. Its purpose though, I easily understand. This is where the computer is going to measure it's resistance from. From THIS wire to the RED / ground wire.


How this all comes together:

When the TPS is not pressed in, the SLIDING PIECE is all the way forward, with the leads as far as they can get, on the RM, from the wires. At this position, all of the leads ARE connected together, in a way. But the current is traveling from the YELLOW wire, all the way to the end of the RM, into the SLIDING PIECE, to the right side RM all the way to the OTHER end of the RM on that side, to the RED wire / ground. So lets call the distance from the wire contacts to the opposite side of the RM 1 unit of distance. The current right now from YELLOW to RED is going 2 units of distance. 1 on the YELLOW side, 1 on the RED side. The resistance here should pretty much be 1k Ohms.

When you push on the TPS, the SLIDING PIECE moves, along with it the two leads move about 3/4 of a unit down the RM. Now, in a way you would think this wouldn't increase the resistance.. or I wouldn't. Because as you move the LEFT side closer to its' lead you're decreasing the resistance there. But as the RIGHT side moves in, it's getting further away through the RM from the RED lead. So it would stay the same right? Decreasing on one side, increasing on the other? Hmmm...

Somehow it doesn't though... the resistance increases as you push it in.

The only way I could think of it working is if the LEFT / YELLOW side of the RM is not RM or resistant at all. In which case this makes perfect sense, you slide along the YELLOW side and it makes no difference, you slide along the BLUE connected to the RED side, you increase the distance it has to travel through the RM and the resistance goes up.

So anyone want to tell me how it's actually working?

And why can't we just use a NORMAL variable resistor rigged to work like one of these? It wouldn't be that hard... not $350 hard at least.

--Gary

RETed

Sure, if you're willing to sell them at $10 a piece, I'd buy 100 of them from you.


-Ted

Bob_The_Normal

I'm looking into it now... not sure it can be done for $10 a piece, I'll let you know what I come up with.

I'm sure it could be done for $10 in mass quantities... but I think plastic casings would need to be made... not sure how much that costs. And I don't think that without some experimenting it'd be nearly as reliable as a new stock one... there's a lot to take into effect, especially the heat conditions it has to operate in. Still... I'll look into it.

--Gary

Parastie

Ever play with those electric race car tracks as a kid? You know, the one with the guns that controlled the speed of the car? The TPS works nearly identical to that, but in reverse.

Technicially, you can use whatever you want for the signal as long as it's identical to what the original. It's like relays, you can either spend $20-50 for a car relay or pick up a $2 12v relay from radio shack. What's the difference? The car Relay is tested for the heat and environment of the car, that testing (and supply/demand) cost money. I've used the Radio Shack relays though (have one now firing the EFAN) with no problems.

A standard variable resistor should work, but getting it connected and tuned properly would be hard and who knows how long it would last.

WAYNE88N/A

How can you possibly call an auto part a piece of **** when:

1) they last a good 15 years (in my case almost 18 now)
2) they function through outrageous temp extremes while still outputting calibrated puny voltages (as Parastie refered to)
3) a normal wiper-type potentiometer would have burned out 10 years ago, or more
4) for a relatively low price (relative to other "moving parts" on the car), you can purchase another that will last another 15+ years

Look at the electrical schematic for this puppy in the FSM- that tells me all I need to know, I don't need to tear it apart to figure it out, lol.

Now the boost sensor, on the other hand, is not schematically represented, and WhiteFC did a hell of a job tearing that thing apart (some of you may remember the thread we had going on this about a month ago) so we could figure out what that 12vdc input was doing...

Drag'nGT

TPS: Throttle position sensor

FSM: ???

Tiers

FSM - ****** stupid motor
(actually FActory Shop MAnual)

Drag'nGT

Aahhhh

2ndGen.rocket

Actually, Factory Service Manual.

SureShot

The inside



the worn out resistor



the worn out slide

Bob_The_Normal

Thanks SureShot! =)

--Gary

Kenteth

Interesting, is there any possibility of repair (just curious)...

Aaron Cake

iTrader: (1)

It's just a slide pot. Available at any electronics store for less then $5. Here's the problem though. If you buy a generic pot, it is up to you to mount it, and keep it VERY sealed from the weather. Slide pots will die a quick death with any exposure to contamination. I guess you could mount it in a case with a pluger, then use a diaphram to isolate the plunger from the actual pot. But that's a lot of work when you can find good used TPSs for less then $20 all day long.

Really, the factory TPS is not bad at all. Consider how old they are, and what kind of conditions they have lived through for 15+ years.

If you want a part that will last nearly forever, you can buy military spec "ruggedized" pots, but be prepared to spend over $300 and still have to figure out a mounting system.

Now, you could find another more modern car with a TPS that produces similar values, make a mount, and use it instead. But is it really worth the trouble for a part that might have to be replaced every 10 years?

Bob_The_Normal

I'm not saying anyone did a bad job, but **** happens... sometimes they just go bad and maybe I don't WANT to take the chance of having a $20 used one that is now at least 15 years old. My point is, why are these not rebuildable? As these cars get older you're going to find these getting rarer and rarer, it'd be nice to have a rebuildable replacement... even if it did last a few years LESS than the factory ones.

--Gary

Aaron Cake

iTrader: (1)

You could probably rebuild if you can find a pot that will fit in the case, but you can't really repair the existing pot.

I'm not too worried about running out of TPSs as the cars get older. Mostly becasue I have sourced a replacement pot that easily mounts up with a minimum of fuss, and has the same values of the stock unit...When we run short, I'll start selling them.

NZConvertible

No, the point is why would any manufacturer bother to make it rebuildable? It would considerably increase the design and construction costs of a part that is far easier and in the long run cheaper simply to replace. How many other parts of the car are rebuildable? Very few...