I have a 15 f150 lariat with a 5.0 coyote bought it used at dealership with 125k. 4mo later misfires on cylinders 3.5 and 8 .I replaced COP's and plug on all cylinders. Misfire returned took to shop cylinder 8 was dead at 22lbs fuel pressure 3 and 5 were at 92lbs pressure was bleeding past the rings according to shop. So they quoted me 15k for engine swap. I bought reman/ rebuilt from fraser who out sourced it to Summit Racing who intern got it from Apple Ford.with 5 yr unlimited no fault warranty had local shop install saved maybe 3k from original quote. within 1month after new installation the misfires on 3 and 5 returned. 2weeks ago I had new COP wire on 3 and 5 installed as wel las new injectors. Yesterday cylinder 3 and 5 threw PO300 PO303 and PO305. Im at a loss as to what direction should i be trouble shooting / repairing. so Im seeking the following advise and direction.
1 which forum should this issue be sent to to address these issues?
2. Is there a way that Ican troubleshoot the PCM?ECM my self to determine if the issue is stemming from it as opposed to mechanical issue?

 

Quite unusual for the same cylinders to repeat on a different engine. Was a short Block installed or a complete engine?
What was done on the original engine....Compression testing or Fuel pressure testing, big difference between the two.? A need to understand what's going on! It's not making sense!
In depth testing with a good higher level Scan Tool is in order but you must know what the live data means.
Codes are only indications of an issue. Need to go to the cause of them and not guess.
Good luck.

 

its a complete engine minus intake the first shop tested compression and fueland rings that how they determined the engine needed replaced

 

a lot of what you are saying isn't making sense, I think you need to take it to a shop that knows how to trouble shoot the issue and find the root cause.

 

Had the same issue 2.5 years ago with my 5.0. Cylinder 8 was done. $13k engine replacement (new).

 

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It's either a co-incidence , not very likely, or a new set of issues.
300 code is misfires detected during Starting/cranking. Code does not ID the cylinders in misfire.
If the old Ignition parts were re-used, they may be faulty.
That would be the false coincidence, for the original issues.
Only other possibility is the Crank Position Signal may need to be reset. Dealer only unless you have a Scanner that can do it.
That should have done as an instruction for replacing the engine, using the same PCM.
It's a Timing reference for everything else that does any timing events.
Crank rotation time, and fire order, Cam positions are the main ones.
Good luck.