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A buddy of mine is having as issue with his 92 NA. The engine is all stock no modifications are present on it (although we suspect the previous owner has forced induction of some kind in the past). It started with rough running and eventual power loss. It sounded like a Subaru at idle, so I went through the usual steps to find a misfire. We pulled plug wires one by one looking for which hole had little to no idle drop and found cylinder 3 to be the issue. We tested spark and found it to be present with good KV output so we ruled out spark. We compression tested the engine and found 180, 175, 176, 175 psi from 1-4 so mechanically it seems healthy enough. Next we inspected the injectors and discovered he was running 3 stock 1.6 injectors (in cylinders 2-4) and a single ~400cc RX7 injector (in cylinder 1), so we decided to replace all 4 with stock 1.6 injectors to see if this would solve or at least help the issue. It hasn't despite the injector for cylinder 3 having an out of spec Ohm reading prior to the injector swap. Now cylinders 1 and 3 seem to be having problems which leads me to suspect the injector part of the wiring harness has a short or open. After looking at a wiring diagram, it looks like cylinders 1 and 3 are both controlled on the low side by pin "U" on the ECU, so my assumption is this could be where the problem lies. My question is does this make sense to others? I haven't seen a car/diagram before, despite having several ASEs and being in school for auto repair and technology for 3 years, that has a single wire controlling 2 injectors on the low side (I'm sure it's fairly common just a little different to me the first time I saw it). Can someone confirm my thinking makes sense? It would give me a little reassurance to start probing the harness and digging out his ECU to pin out the wires to test for shorts or opens. Thanks for taking the time to look at the diagram (see my imbedded link for the diagram I'm using) and either confirm my suspicions or tell me I'm insane.
 
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