Engine miss developed in my 4.6

[Kane]

My stock 4.6 with 116k on it has developed a "rough idle" and engine miss on acceleration. Knowing enough about cars to be dangerous, I self diagnosed and said "plugs and wires". I bought a kit, plugs, wires and 2 coil packs and installed them. Ran smooth and I was proud of myself! I thought I had fixed it!
Now, after about 25 miles, the symptoms have returned. "Check Engine" says "misfire #8" I cleared the code and while the "rough idle and missing” continues, the check engine light has not come on again (yet).
Injectors?
Ideas? Thoughts? I hate just throwing parts (monney) at it without and idea of what went bad!
Thanks in advance!

 

[theterminator93]

I'd start with basic maintenance and tune-up items. Which parts did you use? What did you gap the plugs at? Any signs of coolant anywhere near the plug wells or at the crossover or heater core outlet on the intake?

Other basic maintenance items include cleaning the MAF sensor, replacing the vacuum lines (including the hoses in the passenger fender for EVAP), fuel filter, air filter etc.

 

[AdamG]

Sounds like a possible intake manifold issue. Check and watch your coolant level. Had several work vans that had intakes fail, cylinder 8 misfire was always the first clue. That area of the intake has intake air and coolant very close together and if the o ring gaskets start to fail or more commonly the plastic actually cracks, once the system pressurizes it will force coolant into the intake runner and then cause a misfire, especially at idle. Do you still have your old plugs? If so, do you know which one was #8 and how does it look?

 

[MadMikeyL]

First thing I would do is swap back to your original coil packs. The Ford ones pretty much NEVER go bad (I have literally only ever seen one bad one in 20+ years as a mechanic) and the aftermarket ones are often junk that don’t last more than a year. Hopefully you didn’t throw out the Ford coils yet. If going back to the OEM coils doesn’t fix it, then my next suspicion would be the intake manifold like others have said. The intake cracks and leaks coolant, which then pools up in the spark plug well and causes a misfire. If you pull the plug wire for cylinder 8, if the bottom of it is all wet, then that is likely your problem.

 

[Green T]

What was the exact code?

 

[Derphound01]

The first thing I would do is get rid of the EasyRod body. That will fix a multitude of issues.

It sounds like a coolant leak at the manifold. As others said, check for liquid. I have seen coil packs corrode at the wire connections, but otherwise Mike is right about them never failing.

 

[Green T]

The first thing I would do is get rid of the EasyRod body. That will fix a multitude of issues.

It sounds like a coolant leak at the manifold. As others said, check for liquid. I have seen coil packs corrode at the wire connections, but otherwise Mike is right about them never failing.

You have to look past that. Underneath it all, its an MN12, with MN12 issues and repairs.

 

[Grog6]

Misfire on #8 is usually coolant leaking from the rear of the intake manifold, into #8. If the plug wire gets boiled in coolant, it's bad. They leak spark, and cleaning doesn't help.

 

[Grog6]

Also, doing the crack pipe or Apten mod takes the pressure off that coolant port, that is dead-headed by the intake.

 

[Derphound01]

You have to look past that. Underneath it all, its an MN12, with MN12 issues and repairs.

I just can't. No matter how hard I try, I just can't take it seriously.