We got finished rebuilding the LQ4 in my sonís Ď99 Silvy 2500. When I say rebuild, it was a FULL rebuild including reworking engine harnesses etc.
Basics on the engine are new flattops and LQ9 connecting rods in it, 0.020 overbore, 317 aluminum heads which were port matched, LS2 springs, rocker trunnion kit, LS7 lifters, new pushrods with a TSP stage 3 low lift cam , 216/220, .550/.550, 112 LSA.
Issue started when we went to fire the first time. I screwed up when I put the driver side ignition coil harness back on and reversed it. So it was misfiring kinda hard for a little bit until I figured out what I did. Flipped it around and still had misfiring going on. Mainly 1,5,7.
The harnesses were old and the injectors were origin sly so we replaced the injectors and driver side harnesses and it got a lot better. But I am still getting a miss out of the #1 cylinder.
I can pull the coil plug and it doesnít change the rpm on #1. All the others have a noticeable change. I do hear a change when I pull the injector plug as it seems to smooth the engine out.
Either way something isnít right. I plan on checking compression to make sure I didnít mess something up with running it misfired. Iíve moved coils, wires and plugs but it didnít follow. It is consistently the #1 misfiring.
The only other thing might be this and Iíd like someone to chime in on. The ground wires that I think are for the ignition coils harness on each bank went to a stud in the top center of the block when we put it all back in the truck. (It was 6 mos from pull to reinstall, things didnít go back exactly as they came off, big puzzle) I believe now they were suppose to go into the back of each head. Iím wondering if that is enough to cause #1 not to fire correctly? Basically a bad ground path?
Anything else I can check? Any suggestions?


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