Hello, So I have a 2003 Mustang GT. Has your typical upgrades such as cams, intake, exhaust, tune, etc. about a month ago I started getting a misfire in cylinder 1.

I switched that COP to cylinder 4 and that cylinder started misfiring, so I figured ok it MUST be my coil! So I went and got new spark plugs and a new coil, and cylinder 4 STILL was misfiring. So I got a used set of injectors from a crashed mustang that we’re working great! I put them on my car, and the misfire was STILL on cylinder 4!

Next I compression tested it and every cylinder was reading the same PSI so my compression has to be good. I then pulled my intake manifold (replaced that about a year ago) and I cleaned that area up, inspected everything, threw new gaskets on it, and put it back on. Problem still there.

I then cleaned up all of the COP/injector plugs with electrical cleaner, and the misfire went away! Then it sat overnight and now today it started misfiring on cylinder 7 and it’s throwing p0316 and p0307. I took those connectors apart and cleaned them real well and the problem is still there. I have been looking at the gauges and data logs and everything seems to be normal, except for that misfire in cylinder 7! Any ideas?

Aside from the parts I listed above as being replaced, I have also replaced the MAF sensor, cam and crankshaft position sensors, and fuel pump

Before anyone suggests the cams as being installed incorrectly, they are stage 1 comp cams, and they were installed about 3 years ago by a highly reputable performance shop.