TWSTD wrote:The reasoning behind the "common injector ground" is this:
My question: "Pin 18 on the 18 pin harness is "INJ ground" - is this just any earth? or a special earth point? I currently just have it earthed.
Answer: Thats a problem. It is NOT plain chassis ground _ Though it ends up there eventally. Pin 18 MUST go to the ECU wire that is common to all 4 injectors. The injectors fire when and for the length of time that their ground is pulsed. In order for the INJ map to add fuel it must hold the ground a millisecond or 6 longer. If its not on the same wire as the ECU to INJ then the ground differential caused by the chassis cause the signal to be lost. On mine, the ECU wire was a different color (WHITE/blackstripe) than the common wire visible on the injectors (Brown/Red Stripe) . I had to get an factory electrical manual to find the pin. Until then it ran LEAN UNDER BOOST.
Pure, unadulerated, Bullsh!t
There is no common injector ground wire, there is only a common injector power wire. That said however he does make one correct point, in that the earth needs to be the same as the ECU Earth connection, or the potential difference may cause some problems, not enough to make it not run though.
The factory ECU seems to have many grounds - assuming any will do, thats currently how I have it.
There are three ECU ground pins (E1,EO1, & EO2), but only two connections, one on the engine block and one on the intake manifold. The ECU pins are connected to both, but I can't see a reason why you'd have to do that, so I'd just attach it to the one on the intake manifold.