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Discussion Starter #1
So the car in question is a UK spec TT originally an auto - now converted to 6 speed manual using a bmw gearbox and still using the stock auto ecu.

Mechanically everything seems to be working fine, but I have a low rev limiter issue. So far I have tried a few things:
I have bridged the NSW in the gearbox connect for the car to start. Without this the starter will not engage so this is essential. So far so good. However standing still or in motion I have a 5800 rev limiter. Tried disconnecting the NSW after starting using a relay, but the low rev limit is still present and nothing actually changes.

Then I decided to try and fool the ECU that the car is in a gear (like when you move the gear selector to L, 2, D). Now two things happen here, does not matter which exact gear I select:
1. If I leave the NSW bridged and select some gear nothing really changes.
2. However if I disconnect the NSW and select a gear, the car bumps a bit the idle (perhaps expecting a load from the gearbox since a gear is engaged?). But then things get even worse, if I press the gas I get a rev limit around 4000-4500 and it gradually falls down to 3000 and stays there.

Maybe when the car is in gear the ECU expects to see data from the gearbox speeds sensors and since they are not existing anymore it cuts the revs, thinking the car is standing still? Or maybe the ECU needs something else in order to remove these low limiters? How are people overcoming these problems during manual swaps?
Tried using the search a lot for this, but I didn't find solutions different from the ones I already tried.

Anyone knows what I am missing?
 

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From the land down under
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Are you able to swap in an known working ECU from a 6 speed? That would be a good place to start.

I recall seeing many threads on here over the years in regard to false rev limits, so I will have a dig and see what I can find
 

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Discussion Starter #3
In researching this issue I also stumbled on a few topics where people described similiar issues, but didn't find a working solution in either of these topics.
I even found a strange topic where some guy said he cut the NSF pin/wire on the ecu and the car had a normal rev limiter, but had an NSW related engine code afterwards, with the engine light on the dash etc.

Swapping a good ECU from a 6 speed is what I will ultimately try to do. But finding a 6 speed UK spec ECU is sadly not a simple task. And a Jspec ECU won't work because of different hardware - injectors, turbos, etc.
 

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From the land down under
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Yes, unfortunately, finding an UK spec 6spd ecu will be tough. I was just wondering if any of your car friends may own the same car, so you could just swap it in temporarily to see if it solved the issue.

Does your Cruise control function as normal, and are you getting any fault codes thrown at present?
 

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Discussion Starter #5
About swapping the ecu - looking at the electrical wiring diagrams the ECU pinouts look 99% the same except for the auto ECU which has a few more things for controlling the transmission. Are these ECUs a direct swap using the stock auto harness in the footwell? I can't see an obvious reason why it would not work.
Pity if they are just plug&play since I am far from the UK and this car is the only UK spec where I live, so no one to borrow an ECU from at this point. Only JSpecs and US specs around me :)

Cruise control is something I have not tried yet since the swap. I see it reads speeds sensors and also uses the NSW switch, so it will be interesting to see if it works fine. I will try it next time.
Otherwise the dash is clear from any warning lights and there are no error codes. The car seems to work okay up to the 5800 rpm point.
 

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By any chance did you unplug any modules behind the stereo area while the battery was still connected? Also is the USDM ecu an option? I belive we have the same injector sizes between UK/USDM spec vehicles.
 

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Discussion Starter #7
I also think the injectors and the other stuff are the same, in theory the ECU could be the same as well, but I don't know for sure. Just checked the part numbers and they are different between US and UK spec ECUs for the same spec (a/t - m/t). It could be something small, lets say some emissions stuff, but who knows.

At first I did not touch anything behind the stereo area - I swapped the drivetrain, installed a clutch pedal with a master and a slave, bridged the NSW and went for a test drive. Which is when I first noticed the 5800 rpm limit.
However at that point my speedo was not adapted yet, which was something I fixed a few days after this initial drive. This was done by installing a speed interface between one of the ABS sensors and the speedo input. Connecting all this I disconnected the ABS ECU, which is exactly behind the stereo - can't remember if the battery was disconnected at this point, but probably not. Do you think this could of caused an issue?
But still, the main problem was there before I did all the speedo conversion stuff.
 

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I also think the injectors and the other stuff are the same, in theory the ECU could be the same as well, but I don't know for sure. Just checked the part numbers and they are different between US and UK spec ECUs for the same spec (a/t - m/t). It could be something small, lets say some emissions stuff, but who knows.

At first I did not touch anything behind the stereo area - I swapped the drivetrain, installed a clutch pedal with a master and a slave, bridged the NSW and went for a test drive. Which is when I first noticed the 5800 rpm limit.
However at that point my speedo was not adapted yet, which was something I fixed a few days after this initial drive. This was done by installing a speed interface between one of the ABS sensors and the speedo input. Connecting all this I disconnected the ABS ECU, which is exactly behind the stereo - can't remember if the battery was disconnected at this point, but probably not. Do you think this could of caused an issue?
But still, the main problem was there before I did all the speedo conversion stuff.
I used to have a false rev limit around 4800 a long time ago. It started after I disconnected the ABS module while the battery was connected (Key not in the ignition) as I wanted to run some wiring for A/F gauge and allow it to be controlled by the factory light dimming knob. I ended up disconnecting the battery and reseating the connectors for the abs module leaving it disconnected for a while before reconnecting it. after that, I connected the battery again and the car started to operate like normal again.
 

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Discussion Starter #10
The story continues.

Swapped with a UK manual ECU today. Car started right up, but still has the same 5800 rpm limit, so I started digging in the wires again. Alot of the possible solutions I saw connected to my issue were mentioning the vehicle speed sensor #1 signal (VSS input on the ECU). The ODO gets the speed info for the mileage from the sensor and sends it to the ECU. The odo itself works fine and I traced the wire to the ECU VSS input - perfectly fine as well.
There is a possibility of a cold joint in the ODO (common issue), which is fixed by splicing two wires behind the ODO - tried that as well. No difference at all, still the same low rev limit. The ECU is confirmed to receive proper VSS signal, so this is not an issue regarding (at least this exact) VSS signal.

However, I have some new observations.
1. This low rev limit is not always present - it depends on how you use the throttle pedal. This was the same even when the car had and auto gearbox and ecu and you were in Neutral/Park and tried to rev the car. If you smash it to the floor it will cut at 5800 rpm. If you are more gentle, say 60-70% throttle, it will rev to ~7000 rpm. The car now behaves exactly the same way.
2. So with the knowledge that this happens only on WOT I tried disconnecting the TPS for a test. And voila - the car revs perfectly fine all the way up to ~7k rpm. But that of course immediately throws a TPS error from the ECU, so is not a real solution. Just a pointer in the right direction maybe?

So to sum it up - now with manual TT6 ECU, ECU receives proper VSS signal, low rev limit is only on WOT, does not matter moving or stationary, disconnecting the TPS resolves the issue, but obviously causes error codes.

@NotyMKIV I tried disconnecting the battery and ABS module, but sadly that did not help.
 

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Blue Thunder
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Have you calibrated our TPS or moved it at all? I had this issue and once i calibrated the TPS all works fine now.

I'm going maual soon and I should be able to use my auto VVTi ECU wired like you have done and there be no issues.

B
 

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Discussion Starter #12
Did you have any other issues before the TPS calibration? Did you had the problem only stationary or even while moving? Anything else out of the ordinary?
Asking because I have never messed with the TPS, but it may still need some calibration after 28 years of driving :)
 

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Blue Thunder
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Did you have any other issues before the TPS calibration? Did you had the problem only stationary or even while moving? Anything else out of the ordinary?
Asking because I have never messed with the TPS, but it may still need some calibration after 28 years of driving :)
Dude ... like you said ,it's 28 years old ! ou even said the problem goes AWAY when you unplug the TPS. Test, and Calibrate the TPS or replace it. Problem solved. Sheesh.
 
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