Hi everyone I have a heck of a problem. I have an LS1 in my off-road car being controlled by a MIFI computer. Car last year was completely re-wired and I’ve put 1500 miles on it with zero issues. Last trip out it started running awful, first thing I thought was injectors as I’ve had a similar issue. I sent all the injectors out and they came back OK and I’ve used this company 3 other times. I have cylinders 3,4,5,6,8 all dead. I’m using an infrared on the exhaust and I know they are dead. So I swapped the coil, no change then the plug, no change then the wire, no change. I read about broken springs, I pulled the valve covers and BAM I found a broken spring and a loose rocker. I call an engine builder friend and he sends me out some new springs and I install them. I decided when I had the rockers off I would do a leak down, this would be the best time, all cylinders came back very good I was impressed. After I got new valve seals and springs installed I fired it back up and still no change. I have a Noid light and all the injectors are pulsing as should, I compared each one to a cylinder that is OK. I then bought an in-line spark tester, all cylinders appear to be ok, I tested that using a good running cylinder. The last thing I did was a compression test and they were all from 178 (lowest) to 192 (highest) with an average of 188 so I think that’s fine. I’m at a loss here, I can’t see it being a crank or cam sensor. I checked my big cannon plug in the motor and All pins OK, fuel pressure is at 61# like I said this car has 1500 miles with no issues so I can’t see it being a wiring issues considering I feel injection pulse and spark are present. Let me know what you think to check next, I’m going to use jumper cables to try as a ground to see if something odd is going on.