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The mkiv Supra Owners Club

Removing the TRC System


Paul Booth
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What we know so far.......

 

Of cause one problem you will have is the flap on the auto is also used to reduce torque through the drivechain during shifts without it the clutches are taking full force of the engine every shift, which isn't good for them.

 

-----

Rich

 

Why do Toyota fit the 'OFF' button if it damages the gearbox. Isn't that a bit risky with warranty issues?

 

As noted on another thread, mine changes gear much more smoothly with the TRAC off and I would have thought the jerks on the drive chain were as damaging.

 

Why would HKS sell a unit which damages the car and isn't that why they have an auto specific adapter kit?

 

Answers to these questions, and many more, can be found coming to a thread near you, soon.

 

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P.B.

 

 

I'm pretty sure the OFF button only switches the TC use of the butterfly not the gearchange use.

 

-----

Rich

 

Well......

 

I spent until 01:30 last night reading "The Good Book" and from what I understand:

 

Hitting the disable button simply hits the TRC ECU with a momentary earth to signal user intervention.

I too surmise this only prevents it applying any action under slip conditions although this is logical surmise, not stated fact.

 

TRC is only active during up-changes, NOT down-changes. This much is stated.

This does not agree with the evidence, as I have proved, supported by a third party, that gear changes are smoother, down *definitely* with TRC disabled.

 

The fault diagnostic chart for lumpy gear changes includes the TRC ECU as part of the fault finding.

 

The TRC is slave to the Engine ECU and is linked in with the EFI function.

 

There is no differentiation between j-spec and uk-spec in the book and it includes a hydraulic pump in the functional  description for *all* JZA80 models.

 

Again, surmise, it appears all activity but the sub-throttle butterfly and braking are controlled by the Engine and ECT ECUs and, other than under slip condition when the TRC is considered part of the brake curcuit, the TRC is the slave controller for the sub-throttle.

Incidentally, the Engine ECu could perform the same function using the main throttle, so why doesn't it.

 

In the fraction of a second that the ECT changes up, any action by the sub-throttle is going to be way too late and this appears to me to be similar to the slip function, too little - too late and pointless.

 

Let's face it people while their hardware engineering is first rate, I have personal experience to support the fact that the Japnese are CRAP at software solutions.

 

If Leon is burning clutch packs, I think this is down to power applied and not  throttle control.

 

To reiterate, my car changes down demonstrably more smoothly with TRC disabled and this flies in the face of the the book.

I didn't think to pirate an engine repair manual (but it's on my list) so I'm hoping Ash has one and we can tie the action of the sub-throttle and the EFI/timing to ECT up-changes.

 

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Quote: from GavinL on 10:13 am on Aug. 19, 2001[br]Hi...

 

I found this on the US site, if the manual is correct a J-spec car should have all this gubbins as well as the UK spec.....anyone got their bonnet up?

 

http://www.mkiv.com/techarticles/no_trac/

 

 

Im not exactly sure what Im supposed to be looking for in that picture...?

 

Also bear in mind the brake master cylinder is on the opposite side of the car to the UK and j-spec cars.

 

JB

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Paul........

 

I think what you need with your car is to get everything working as stock, before removing sub-throttle buterflies, etc.

 

The key, to my mind, is to investigate the error code 42 you talked about in another post. Get that fixed first and the car running properly.  

 

Yours,

J  

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Ash,

 

I *know* where code 42 is coming from. It's the output from the pulse shaper in the odo.

 

The Pink wire isn't making with the back of the odo properly and, contrary to popular belief, you can't just link the wire from Sensor No 1 straight to the Engine ECU, PPS, Cruise, etc. as the signal needs pulse shaping (i.e. squaring off) via the odo first.

 

If I'm absolutely forced into it, I can solder the wire directly to the odo, but I'm gonna be real desperate for that to happen.

 

The ECT uses Sensor no 2 for it's speed data and Sensor no 1 is only a 'back-up'.

 

It's a very intermittent fault anyway, so I'm going to look at tightening up the female pin in the odo connector this p.m..

 

This is a minor problem and unrelated to my previous performace issues.

 

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Quote: from Phil Wall on 12:25 pm on Aug. 19, 2001[br]Should the pink wire from the odo beconnected to anthing.

Mine is cut as per JIC

 

I dont have top end speed problems.

 

But might I have other problems that  I don't know about.

 

The JIC converter feeds an 8/5 pulse train into the speedo but they then use a UK odo which already handles the miles v Km issue. Then, to get around the speed limit issue, they cut the square pulse signal output from the back of the odo and feed that with a limited signal from the converter, output 2.

 

Now I have yet to determine whether it is frequency limited, i.e. it delivers an accurate input/output response up to the limiting figure and then caps it off at that point, or whether it uses the same 8/5 pulse train.

 

The problem with this is that you're not providing accurate data to the PPS, etc.. There's an argument (which I'm inclined to buy into) which says beyond 112 mph the characteristics of the PPS, A/C amplifier, Cruise control, etc. are irrelevant anyway.

 

Now if I *was* correct, why would HKS do an SLD device for the manual and one for the auto. This leads me to believe that the JIC solution is probably perfect for manual boxes but there are hidden issues on the auto.

 

Therefore, I will go with the safest route, i.e. use the JIC converter for the speedo but leave the square pulse output from the odo driving down to the Engine ECU where I will fit the HKS SLD. Hopefully, once I've seen where that wires into on the auto it will give me the necessary clues as to what's going on with the TRC.

 

I feel confident removing the butterfly and braking components of the TRC immediately as (a) It's a waste of space & (b) by leaving the electronic interaction between the TRC ECU and the engine ECU in place, you ensure any timing/EFI function exist during up-changes.

 

The flashing light referred to on the US site will be bacause the sub-throttle actuator has a position sense feedback and if it doesn't 'see' any movement it will report an error code. I'm going to look at mechanically connecting the actuator to the sensor when I remove the butterfly.

 

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The JIC converter feeds an 8/5 pulse train into the speedo but they then use a UK odo which already handles the miles v Km issue.

Are you sure they use a UK Odo most places solder a connection in the back so it shows the "MILES" instead of "km" LED and just convert the read milage down, then use the same box they are using to convert the speedo to convert the Odo. It seems strange they would go to the expense of a UK Odo when a Jap one can be converted for virutally nothing. (maybe that's why their cars are so expensive)

 

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Whatever.

 

You might be right that they have the divide link on the back of the odo swapped, I just remember they referred to the cost of 'buying' the units and having them converted, which I assumed at the time to be 'clocked'.

 

The effect is the same as far as the loom wiring and pulse shaping is concerned.

 

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But didn't I hear someone say they convert the odo to read the equivalent miles? In which case it's a chip-change or a UK unit that's been clocked with a sig-gen to whatever reading.

 

Yours,

J

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Yes they do translate tro miles. My conclusion exactly, i.e. UK odo fed with a sig-gen.

 

I assume you've looked at the odo; you'd have to pay me a lot to want to swap that rather large quad flat pack sitting under the CCF display panel, with likely lifting pads during seperation. It's just not worth the labour costs.

 

No thanks, UK odo and sig-gen for me, thank you very much.

 

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I fitted the HKS ETCS removal kit at the weekend and have the problem of flashing warning lights.

 

The 'OD OFF' and 'TRAC' flash in sequence, which is the same problem you get if you disconnect the 4-pin wiring plug from the spring housing of the l/h side of the throttle body (as you look from the front of the car).

 

I'm guessing that there is a missing signal but I can't decipher the electrical manuals on mkiv.com to work out how to fool the car.

 

Anyone got any ideas?

 

 

(Edited by Phil at 3:37 pm on Aug. 20, 2001)

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Do you have this problem when you first switch on the ignition or after you've started the engine/moving?

 

All the circuits are self testing so just disconnecting them is always going to upset it. You have to either leave the circuits electrically correct or take the bulbs out.

 

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There is a metal disc with 2 contact points, and I suspect reed switches or similar, in the spring side which I have tried re-fitting in both positions to fool the ecu but without success.

 

I'm wondering if it takes a signal from the motor on the other side of the throttle body but until I know what is expected I can't sort out a work-around.

 

The instruction sheet is in Japanese (obviously) but even the pictures are rubbish really, I've had a quick look on the 'net but haven't turned up anything useful yet.

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  • 5 years later...

Well thats the end of my search and no conclusive answers on how to fool the ECU into thinking the trac is connected.

 

Ive just finished making my own throttlebody, but with the trac gubbins disconnected, I lose manu mode and get the flashing lights.

 

Any ideas gents?

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