Manually swapped TT Supra - 5800 rev limit issue.

[happ3n5]

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 can 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?

[Mike2JZ]

Typically you don’t have to do anything special, just bridge NSW and away you go.

Auto ECU always do funny things on a manual car due to it missing any inputs from gear box. Your will also not make as much power as you could. Your best option is to plug in a manual UK ECU.

Also, UK ecu’s are very sensitive to most types of error code. If the ECU detects a fault it is important that you fix the fault as soon as possible, otherwise you may be put in a limp mode, depending on the fault. Jspec ECU does not suffer from this typically. 

[happ3n5]

Yeah that's what I have seen - just bridge the NSW and that's it, but in my case it does not work. 

The manual ECU sadly is not plug and play even if I have one - I have looked in this option and the ECU pinout together with the loom are different. Jspec ECU would not work on my car due to different hardware - injectors, turbos, etc..

The interesting thing is that I don't have any errors - the dash is completely free of any error lights and the car starts and goes pretty much as normal right until 5800 rpm. So even if the ECU detects that something is not okay it is not reporting anything to me to check and fix.

Any other ideas what I could try? At this point every little suggestion is worth the try.

[Burna]

11 minutes ago, happ3n5 said:

Yeah that's what I have seen - just bridge the NSW and that's it, but in my case it does not work. 

The manual ECU sadly is not plug and play even if I have one - I have looked in this option and the ECU pinout together with the loom are different. Jspec ECU would not work on my car due to different hardware - injectors, turbos, etc..

The interesting thing is that I don't have any errors - the dash is completely free of any error lights and the car starts and goes pretty much as normal right until 5800 rpm. So even if the ECU detects that something is not okay it is not reporting anything to me to check and fix.

Any other ideas what I could try? At this point every little suggestion is worth the try.

UK Manual ECU

[TheTurtleshead]

I had this issue, made a thread years ago. There's a wire you have to cut on the ECU plug end. 
 

[TheTurtleshead]

 

[happ3n5]

Yes, your thread popped up with the search funtion, but I also saw you had in error code as a result of cutting the wire. How did you fix this?

[TheTurtleshead]

Ignored it!   
 

Really the best fix is indeed a manual ECU.

Edited January 9, 2021 by TheTurtleshead (see edit history)

[happ3n5]

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.

 

@TheTurtleshead, I was busy with the manual ECU stuff and did not try your solution with cutting the NSW wire. But this should not be needed, since the car has a manual ECU now.