Answered: How to get a US p28 ECU to work with a JDM ITR motor!
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From: Richmond, Va, USA
Answered: How to get a US p28 ECU to work with a JDM ITR motor!
Hi folks,
We finally figured this one out with the help of several friends and on-line resources. There was so much partial info to wade through I thought I would pass the learnings along so others could use it.
The issue:
JDM motors don't have a VTEC pressure switch. US ECUs need the signal from this switch or else they throw codes and don't go into VTEC.
How do you make it work:
Option 1: Simply splice the VTM (Vtec pressure switch) line from the ECU into the VTS (Vtec solenoid / spool) line from the ECU
Option 2: Replace JDM solenoid assembly with US assembly that has a pressure switch.
Option 3: Ground the VTM (pressure) wire. Now set up a relay that breaks that ground (ungrounds it, in other words) whenever the VTS (Solenoid) line sees +12 volts. You will need a special relay that can break continuity to do this.
Explanation: On a US car, the VTEC pressure switch is actually measuring oil pressure AFTER the vtec solenoid (in the VTEC "chamber"). ie. it only sees pressure when VTEC is activated. The pressure switch is a push-button type switch that actually breaks continuity when pressure is applied.
At idle and off-vtec, the ECU is applying +12 volts to the VTM line. Since the switch has no pressure on it, it has continuity, and this signal is sent straight to ground. As a result, the ECU sees no voltage on this circuit.
Once VTEC activates, oil fills the chamber with the pressure switch. The switch then "opens", breaking the signals path to ground. Now that the +12v the ECU is sending is no longer grounded, the ECU now sees the potential of +12v on the circuit.
Summary:
The ECU needs to see 0 volts (ground) on the VTM line at idle and off-vtec.
The ECU needs to see +12v on the VTM line when on-VTEC.
If either of these needs are not met, you will throw codes.
I want to thank all of the folks who helped us sort this out. I'm not going to list everyone, but in particular, I would like to thank:
Jamie Edwards
Jack (Cranky, Knowledgeable, & Fast) Harris
Hondata
Doc
G3-Teg
Feel free to make additions or corrections.
-Phillip
We finally figured this one out with the help of several friends and on-line resources. There was so much partial info to wade through I thought I would pass the learnings along so others could use it.
The issue:
JDM motors don't have a VTEC pressure switch. US ECUs need the signal from this switch or else they throw codes and don't go into VTEC.
How do you make it work:
Option 1: Simply splice the VTM (Vtec pressure switch) line from the ECU into the VTS (Vtec solenoid / spool) line from the ECU
Option 2: Replace JDM solenoid assembly with US assembly that has a pressure switch.
Option 3: Ground the VTM (pressure) wire. Now set up a relay that breaks that ground (ungrounds it, in other words) whenever the VTS (Solenoid) line sees +12 volts. You will need a special relay that can break continuity to do this.
Explanation: On a US car, the VTEC pressure switch is actually measuring oil pressure AFTER the vtec solenoid (in the VTEC "chamber"). ie. it only sees pressure when VTEC is activated. The pressure switch is a push-button type switch that actually breaks continuity when pressure is applied.
At idle and off-vtec, the ECU is applying +12 volts to the VTM line. Since the switch has no pressure on it, it has continuity, and this signal is sent straight to ground. As a result, the ECU sees no voltage on this circuit.
Once VTEC activates, oil fills the chamber with the pressure switch. The switch then "opens", breaking the signals path to ground. Now that the +12v the ECU is sending is no longer grounded, the ECU now sees the potential of +12v on the circuit.
Summary:
The ECU needs to see 0 volts (ground) on the VTM line at idle and off-vtec.
The ECU needs to see +12v on the VTM line when on-VTEC.
If either of these needs are not met, you will throw codes.
I want to thank all of the folks who helped us sort this out. I'm not going to list everyone, but in particular, I would like to thank:
Jamie Edwards
Jack (Cranky, Knowledgeable, & Fast) Harris
Hondata
Doc
G3-Teg
Feel free to make additions or corrections.
-Phillip
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