I have been relishing in spending some ‘quality time’ with the car. Since putting it back together the other day, I have been battling an intermittent misfire which makes it run on three cylinders (and sound like a WRX). I did idle the engine with the rocker cover on but not torqued before putting in the rocker arm stoppers which sprayed some oil mist into the spark plug wells. I thought it was this but remember a slight miss on the dyno for the final run. I cleaned the coil packs and put in new spark plugs but the problem would still come and go. Wiggling the coil pack harness while idling would often fix the problem, so yesterday I picked up a 2nd hand unit from SSS Automotive. When I first fitted it, the car still idled on three cylinders, but shortly after it went away and is yet to return.

Yesterday I pulled out an injector to try and verify it was a 740cc Nismo as the seller had listed. Googling the numbers on the body told me very little. The A46-Z00 code seems to match everyone’s injectors online, so I assume it is related to the plastic moulding for the injector which is shared across various models. The other ‘0122214’ number is likely a batch number, as everyone posting on forums had a different one regardless of their injector. Visually, the injector looked like most others. Googling Nismo 740cc injectors produced variations in colours from site to site, although most forums agree that Nismo 550cc injectors have a yellow body and the 740cc injectors have red. There is some confusion around the Jap spec S15 injectors looking similar but they appear to universally have a green portion near the nozzle. There was nothing to confirm that they weren’t 740cc injectors but it was still inconclusive.

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I turned to using the tune pulled off the ECU in Nistune as the indicator as to the real size. Starting with a bone stock map, I first altered the tune for an RB25 afm, then various sized injectors. Doing this changes the K constant, which is used to calculate load and fuelling. The RB25 afm/ 740cc combination was closest to the K value in the tune as received.

Another good way to test was to install the Z32 afm, tweak the settings for this and 740cc injectors and see if it would fire up and run. If the injectors were not that size, then the tune should see the engine struggling to run. Fortunately the car fired up and ran very well. I then copied over the fuelling and ignition timing maps from the previous tune, which are more conservative and suitable until the car is tuned. The car is driving at least as well as it ever has. The combo of Z32 afm and 740cc injectors puts the K constant very close to the original, which helps the ECU function as it should. The car no longer goes lean as it comes onto boost which is very encouraging.

The wiring for the RB25 air flow meter was quite butchered, with twist and tape butchery. I disassembled, soldered and crimped on some spade connectors. The Rb25 afm can now be swapped back and forth if the need arises.

I am in initial talks with Unigroup about booking in the tune, which I’m hoping to have done asap. A big thanks to my wife for giving me the blessing to proceed so quickly.

In the meantime I’m going to experiment with cutting and fitting the braided hose that came with the oil cooler kit. It arrived in one continuous piece, which is more customisable but more work. If it is simple, I’ll install it and the winged sump before the tune.