VTP/EPS Intermittent/Phantom Signals

[MortyK20]

Good Afternoon

When posting a KPro problem with your vehicle, please include:
- what vehicle you have - Toyota MR2 swapped with a K20A2 Turbo.
- serial number of your K-Pro - 69166
- version of software being used (from Help, About) - Hondata K-Series Programmable ECU Editor (32 bit)
- ECU part number (starts with 37820) and serial number (the number under the part number) PN: 37820-PRA-E03 SN: 2030-401120
- KManager version (not 'the latest') - KManager version 4.6.1.0 Build 4083
- the calibration (as an attachment) - Morty2 Attached
- a datalog of a problem (as an attachment) 4 datalogs attached
- anything about the car which has been modified from stock which may affect the ECU (don't include what sort of rims you have nor stereo etc).
As it's an engine swap a lot of the wiring has been changed. Engine loom is one of the china looms but has been checked over and works fine aside from the stated issue. Furthermore the intermittent inputs do not run through this loom. Engine is grounded to the chassis from the gearbox. Engine loom is grounded to the transmission side valve cover stud, as well as a link ground to the timing side stud (extra ground added during troubleshooting). Cylinder head is also directly grounded to the chassis with a further ground wire. Engine loom is grounded near the ECU to the factory MR2 ground location as per most swaps eg. hux conversion instructions.
- when and where you got the K-Pro
Kpro purchased from and installed by CPL Racing in the UK - Around August 2025
- a specific description of the problem

Issue #1 - Launch control inputs are not stable. Both VTP and EPS inputs have been tried via a clutch switch. At high RPM, the input which should be ungrounded manages to intermittently ground itself and flicker on and off, cancelling the launch control and allowing the revs to exceed the target limit. VTP input shows as "ON" in the sensor window when ungrounded, even though the launch control instructions state that GND=On. The function is inverted compared to expected. Both VTP and EPS behave at idle and moderate RPM. VTP when grounded shows as "off" but flickers back to on, even when grounded directly from the ECU with a jumper wire (eliminating the clutch switch as a pontential issue) . Similarly with EPS, when ungrounded (no pin present in the ECU), at high RPM it somehow flickers to "on". The 12v E22 brake switch input is being used for high/low boost and works normally at all RPM. Both VTP and EPS inputs can be seen showing this behaviour in their respective logs. All other ECU functions are working normally.

I have tried this on another ECU and the problem is the same.

Issue #2 - Moderate revs (3-4k rpm) when engine is not fully up to temperature causes the ECU to drop into some kind of overfuelling routine and will then fail to maintain idle. Attached are two logs. ColdRev_WontIdle shows the car being accelerated in first gear up into the revs and the clutch being pulled in. The car then dies. It will not re-start without throttle. The engine can be kept alive with throttle, but runs extremely rich. S.term trims can be seen pulling fuel out all the way up to 20% in an attempt to keep the car alive. Turning the engine off, and turning it back on again does not reset the problem. After a certain unknown period of time, the ECU drops out of this regime and then functions normally. This can be seen in cold_idle_recovery log, where it starts off being kept alive with throttle and trims pulling down to -20%. After a brief rev around frame 1800, the AFRs swing back lean and the s.trim has to walk back up to 0% and then idles normally at around 1krpm. It does not do this if allowed to warm up fully. Once up to temp the car behaves normally. I cannot find a reason why it drop in and out of this regime, having poured over the logs. I can't find anything temp related and do not know why it would suddenly overfuel like this. I tried a different ECU and the behaviour was the same.

Both of these issues seem to be RPM related but it's unclear to me why.

Any help appreciated with these two issues. I've tried to be as detailed as possible.

[Spunkster]

Have you tried your ECU on a known working vehicle using their calibration?

[MortyK20]

Have you tried your ECU on a known working vehicle using their calibration?

I don't have access to any other working vehicles that run kpro.

Are there any other troubleshooting steps you can recommend I can take other than what I've done already?

[Spunkster]

This is most likely wiring related as most aftermarket harnesses do not have the shielding that an OEM harness has.

[MortyK20]

This is most likely wiring related as most aftermarket harnesses do not have the shielding that an OEM harness has.

I'll swap it for an OE loom and see if the problem goes away then report back.

[MortyK20]

This is most likely wiring related as most aftermarket harnesses do not have the shielding that an OEM harness has.

I've swapped back in the OEM loom and I'm back up and running again. Unfortunately the inputs are still doing the same thing and flickering at high RPM. Any idea what to check next?

[Spunkster]

Check the sensors themselves and the wiring in any junctions as it may be vibration related if it is at high RPM.

Are you using resistor or non-resistor type spark plugs?

[MortyK20]

Check the sensors themselves and the wiring in any junctions as it may be vibration related if it is at high RPM.

Are you using resistor or non-resistor type spark plugs?

NGK BKR8-EIX for the plugs

I'm just confused why the ECU would read a pin is being grounded when it's not connected to anything. I'm not even sure how that is possible regardless of other connectors. I'll resistance check the ECU to ground to see what the ground continuity is back to the chassis. But I still don't see how that would result in this symptom. I'll also move the body side ground somewhere else to see if that changes. I haven't had any weird readings from any of the sensors I can see in the logs, just the EPS and VTP inputs messing up. Even more confusing that it didn't change with the loom swap or with a different kpro. I'll try the other kpro again now I've swapped the loom to be certain.

As a last resort I'll try the service connector input to see if that does the same thing, however this isn't ideal as it'll put the check engine light on every time the clutch is up. I'm assuming there's no way to disable this behaviour. I'd quite like my CEL to be functional in a normal way.

Do I have any other options?

[MortyK20]

Check the sensors themselves and the wiring in any junctions as it may be vibration related if it is at high RPM.

Are you using resistor or non-resistor type spark plugs?

So a bit of troubleshooting more. Unplugging the alternator makes the issue go away. I'm going to swap in another alternator and see if this fixes the problem.

Is there anything else I should check alternator wise that could cause this?

[MortyK20]

Changing the alternator didn't fix it. Same problem.

I'm a bit lost about what else I can check at this point. All connections seem solid.

[Spunkster]

I would recommend trying this in a known working vehicle to see if it works there without issues.

[MortyK20]

I would recommend trying this in a known working vehicle to see if it works there without issues.

I don't have a working kpro vehicle to try it with.

I am almost certain it's something alternator related. Unplugging the 4 pin connector on the back of the alternator, everything works perfectly.

To add to the problem as well - I tried moving the input to B9 VTEC Pressure switch. This one when ungrounded shows a solid "On" state in Kmanager and does not flicker with RPM. When I provide the pin with a direct ground to hold it "off", it starts flickering the same as the EPS input. So its unlikely to be a grounding issue as the behaviour is reversed. It's always when the input is supposed to be off it flickers to on. When it's in the on state it doesn't flicker to off. So I don't think it's a grounding problem at all now.

What can I check in terms of alternator wiring that might cause this issue? It's unlikely to be engine loom side as this has been changed already. Are there any loom/body side modifications required for running without the ELD enabled?

Thanks

[Spunkster]

I would check with others who have done this swap to see how they have things wired as it sounds like something specific to this chassis that may be causing this.