I've got a weird one I could use some help with. 2013 5.0 has a misfire on cylinders 7 and 8. I've switched injectors, coil packs and spark plugs around with no change in misfire position. Compression was 100psi+ on both cylinders with both plugs out. The only codes I have are p0300, p0307 and p0308. I pulled the valve cover today and the lobes looked great, I even measured lobes on known good cylinders to be sure and the measurements were the same. All coil packs are firing when I lift them up and I have injector pulses when I check with a noid light. I'm at a loss... by all indication this thing should run great, am I missing something? Any help is appreciated.

 

Good sleuthing and work there. You might perform a leak down test. That could show faulty intake valves on those two cylinders. Of course that would be terrible news but at least you would know.

https://www.f150forum.com/f38/2012-x...-issue-562997/

 

Maybe you should do a full compression test with all plugs out or at least do all of bank 2. but all plugs should be removed so engine can turn free and evenly. I'm thinking all cylinders should be at least 125-175 PSI and all should be within 10% of each other. No Cylinder should fall below 100 PSI. So if most are say 140psi that means any cylinder below126psi would be suspect. Any two adjacent cylinders with low compression would indicate a head gasket problem.
Is the miss severe enough that you can feel it?

 

Ty, I may try this, I've heard valve seats could be a problem on these engines. I assumed the compression test would have reflected bad valves if that were the case. Also wouldn't it have "popping" back through the intake?




I actually did test them all with the plugs out, they were all around the same psi. When I was referring to them in my original post I meant to point out that the two with misfires probably weren't bleeding into each other due to a head gasket failure.

Yes, it feels like a dead miss. If I pull a coil wire or injector while it's running there is no change that I can tell.

 

I know you said you thought the coils where firing by lifting them up but do you have a noid light that will connect to the coil connector? A dead miss is usually ignition or fuel related mechanical problems are usually not that harsh.

 

You can use one of those non-contact testers on the coils too I think.

 

I believe the coils always have power to them and the PCM provides the ground pulse to fire the coil/plug.

 

You said your compression is 100psi plus? How much Plus like 101 105 or could it be 150 psi

If anything that compression seems a little low. Do you run premium fuel or the low-grade fuel? Does it get better or worse with heat up cycles? Does it change it all with heat up cycles do you notice or feel the misfire?

I just got done pulling my hair out over a 2014 5.0 with a misfire and it turned out that there was spiders living in the evap canister. So it may be a long shot but you may want to try that.

Someone mentioned the league down test definitely do that.

I don't want to tell you something you already know but just so you didn't overlook the simple stuff how did you spark plugs look where they greasy where they wet they have oil on them are they gapped right are they eroded did you replace them recently did you replace them all? Did you also replace the boot connector between the coil and the plug. Is it getting spark?

 

I'm not sure if my compression tester is very accurate but it was just over 100psi (105 possibly). It does seem to be worse once it's warmed up.

I did check that all plugs were gapped correctly and boots were in good shape. The plugs looked fine, nothing out of the ordinary but they were replaced anyway.

​​​​​​​I haven't gotten ahold of a leak down tester yet but checked compression again today and had 40 psi on cyl 8. All others on that bank were right at about 100psi again with the exception of cyl 7 giving me a reading of 60 psi twice. I know cyl 8 was above 100 when I tested it prior to my original post so I'm guessing there's something wrong with the valves and the way they're seating.

 

How many miles on that engine?