VLT ECU into R31
If you have just put in an RB30ET or turbocharged the RB30E in your R31 with VLT Commodore engine parts, you will need to run a VLT ECU (unless of course you're going to use an aftermarket ECU).
Both the VL & VLT RB30 ECUs will plug straight into your R31 engine harness & are pin-for-pin compatible, however when you go to start it you will notice that the fuel pump isn't running, and therefore the engine will not start/run.
This article is about how to adapt the VLT Commodore ECU for use in the R31 Skyline.
Standard R31 fuel pump control[edit]
When the ignition switch is in the ON position, battery positive voltage (+12v) is supplied to the fuel pump positive (+) terminal via fuse #16 (10Amp). The fuel pump negative (-) terminal is connected via the wiring harness, back to the ECCS ECU pin #108 -- see Pinouts Inside the Nissan ECU, is a driver transistor that can switch pin #108 to ground, and the fuel pump starts running. As the ECU has control of the transistor, it can vary the running speed of the fuel pump, to better suit operating conditions.
Differences between R31 & VLT ECU fuel pump control[edit]
The R31 runs a single in-tank high pressure pump, which is directly controlled by a variable voltage driver on ECCS ECU pin #108, as described above.
In contrast, with the VL/VLT Commodores fitted with RB30 engines, Holden chose to use two fuel pumps -- one external high pressure pump and one in-tank low pressure pre-pump.
Whether as a consequence of that design choice, or other considerations Holden had in mind, the ECCS ECU fitted to VL/VLT Commodore RB30, does not include the variable voltage fuel pump driver at component level, and pin #108 is N/C (not connected)
To accommodate for this, Holden renamed/repurposed pin #16 of their ECU, from Cold Start Valve (air regulator), to Fuel Pump Relay, which does just that -- turns the fuel pump(s) on/off via a relay, and the pump(s) run full voltage all the time. The air regulator in the VL/VLT is connected to the same circuit ; when the fuel pumps run, the air-regulator is also active.
The standard R31 fuel pump in good/new condition, will deliver enough fuel to deal with the VLT Injectors - all you need to do, is recreate the Holden fuel pump relay setup in the R31.
How To Do It[edit]
To get around this you will need to purchase a relay and wire as described below. I used a 5 pin Narva relay, which you can buy from any auto outlet / Kmart.
- Remove kick panel in passenger footwell.
- Unscrew ECU from Body.
- Remove R31 ECU, by removing the 3 connectors.
- Before plugging in the VLT ECU, cut the pure white wire on the 15 pin connector...from the ECU. This is pin #108
- Join this wire from the loom side (Not ECU side) to pin 87 on the Relay.
- Now on the 20 pin connector look for the "White with Black stripe wire", what you need to do with this one is splice into it rather than cut. This is ECU pin #16
- Now join a wire into the white and black wire and connect it to Pin 86 on the relay.
- Run a wire from pin 30 on the relay, and earth it, I earthed mine to the ECU mounting bracket.
- Connect a wire from a 12v ignition power source to pin 85 (I think I used a wire under the passenger seat for the Auto comp which I no longer required, but any will do)
- Plug VLT ECU in, once the ignition is turned on, the pump should run for 5 seconds then switch off. If so everything is fine.
The relay should be wired like this:
- Pin 30 Earthed
- Pin 87 White wire (joined to loom side)
- Pin 86 White with black stripe (spliced into)
- Pin 85 12v Ign power
Notes[edit]
- If you have done all of the above and it does not work, then please check your fuses, as one has probably blown in the process!