Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!
2012 Ford Raptor runs really rough, definitely getting a misfire all the time, DTCs confirm by setting P0301 and occasionally P0305, however when I performed a cylinder contribution test it was as if not a single cylinder was contributing. I could unplug any 4 ignition coils all at once without making any change to how the engine runs. Performed a relative compression test, found no low cylinders, confirmed with mechanical gauge reading roughly 175 psi on all cylinders. I scoped all the ignition coil ramps compared to relative compression and found ignition timing was early on every cylinder, I did the same test to a 2011 F350 with the 6.2l that happens to be at the shop at the moment, on the known good ignition firing events occurred right at TDC, confirming that I have an ignition timing issue. I performed a cam crank correlation test on both vehicles, and also compared to known good found online, all matched perfectly. This makes me want to say the keyway has shifted on the crankshaft timing gear, however on the 6.2 the camshaft tone ring is bolted to the flex-plate and therefore couldn't have shifted. It could also be noted that we had this engine out of the vehicle already expecting to find an issue with the tone ring, I also pulled the front cover while the engine was out and confirmed the timing chain was installed correctly, and nothing looked out of place.
I’m just making this post so that anyone else who is having a similar issue with the ford 6.2L engine running horribly and similar symptoms to what’s listed above, hopefully this will help. The issue ended up being a broken exhaust valve spring, this really threw me off because cranking we had a good 200psi of compression, however we performed a running compression check and found 0psi. Weak exhaust spring meant the valve didn’t have time to close the whole way during compression stroke
