Misfire in #8 cyl

[scattermaster]

I've been chasing this #8 misfire for a while now. I also had lean codes for both banks.
So far I've:
1. installed a new intake manifold.
2. Installed a new PCV valve and hose assembly.
3. Cleaned and tested all 8 injectors. All look good. Moved #8 to #1 position.
3. installed new spark plugs. (#8 twice, + a new COP)
5. inspected all the vacuum lines that I can see. Checked with a gauge at idle and it's pulling about 18hg.(IIRC)


After about 400 miles, there are no more lead codes but I still have a pending #8 misfire and the catalyst and evap will not complete.
I checked fuel trims and I don't remember what the numbers were but it didn't seem like the computer was having to make real drastic corrections. I will say that the 2 banks have different amounts of correction. O2 sensors are responding normally.
I did a compression test today. (cold) All cylinders top out at about 200 psi. About 180 psi at 5 cranks.
I tested all the injector plugs with a NOID light and all 8 look good.
I noticed today that the ceramic near the electrode on the #8 spark plug was white. All the other ones were slightly tan.
I want to do a spark test but it's difficult to rig. When it's installed it's too tall for the coil wire/plug to reach. It's one of the ones with the light. I'm not sure how I'm going to make it happen.
Does anyone have any advice on how to rig the spark test?
thx,
Jim
EDIT:
I took a long piece of #10 wire and attached one end to a bolt on the engine. I attached the other end to the side of a plug. Then used one of the COP's with the that plug inserted and plugged it into the #1 COP connecter and hit the key.
It sparks. Then I moved to the #8 cylinder and did the same thing and got the same spark.
So, it seems to me that I have spark, fuel, compression, and air.
And a misfire...
I'm all out of things that I know to do except put it all back together and see if it went away.
Am I missing something?
Jim

 

[nutter_owner]

I posted for same with 5 cylinder...... why cant someone answer and say "this cured mine of same symptoms"????

 

[JamaicaJoe]

Swap fuel injector for the affected cylinder and see if problem moves to another cylinder. White insulator on plug means a lean condition exists.

 

[MesaGuy]

JamaicaJoe's suggestion to swap the fuel injector is good one, but I would do that second.
I also would not bother with the spark test, it will not tell you anything. You are getting spark! If you were not getting spark (and had a dead cylinder), the 5.4L and the 4.6L will both run VERY rough, missing only one cylinder at idle, and you would know it instantly.

90% of the time, its the COP. And 10% (Plug or Injector). Your "new" COP, is it a genuine Motorcraft COP? If not, then I would say 99% chance its the COP. I have used after market COPs on the 5.4L, and found have this history. With one brand, they threw misfires right away (occasional), car RAN just fine. With a second brand of aftermarkets (a bit more money), I found that these COP ran reliably without incident, for about 12K miles, and they would start to throw misfire codes. Finally, I just bought genuine Motorcraft COPs (at the much higher price).... Price of the 1st 8, was the same as 1 Motorcraft COP. Price of the second 8 (better after market) was the price of 2 Motorcraft COP. Finally, just bought new Motorcraft COP. I you are really on a budget, I would suggest going to the junk yard, and pulling COP off an engine where the vehicle appeared to have a front-end or other crash. (I say use a crashed vehicle, because it was likely running decent until the crash, so COPs probably still have some life in them.)

I did this once when between jobs, and that COP worked flawlessly, until it failed about 30K later. Most of the time you have an intermetent misfire, its the COP.

If you don't want to spend money (at least right away), then I would swap the COPs from the #8 cylinder, and the #1 cylinder. The problem should clear on the #8, and might or might not reappear on the #1. If it reappears on the #1 cylinder, then getting at the plug and the COP is a lot easier in terms of access than the #8 cylinder is.

If the problem remains on the #8 cylinder after you have swapped the #8 COP and the #1 COP, then you have excluded the COP, and that increases the chance of a plug or injector problem. A single PLUG is cheap, (again just use the specified Motorcraft plugs, its one plug) and buy that and put it in when you are swapping the #8 and #1 COPs. That way, if the COP swap does not move the problem, you know its likely the #8 injector getting tired.

The other thing you can do, is just clean the injectors. I swear, the Chevron with Techron black bottle additive is great stuff. If you are having a problem (you are, perhaps), then put TWO bottles in! e.g. 1/2 tank+ bottle, then fill it almost all up, and then 2nd bottle, then top it off. Do that TWICE, e.g. 4 total bottles, and 2 tanks of gas, and if your injector issue is just deposits, the Chevron with Techrom will clean it up. The PEA in there is wonderful stuff. (Other brands with PEA are also fine, but the Techron is most PEA for the buck usually).

I would use the 4 bottles of Techron before I did the injector replacement for sure (so easy, not that much money, on sale, its $20 for 4 bottles, not on sale $40). One plug is $5. The COP's are the pricey item.

But its almost always the COP. And if you used a non-Motorcraft COP, its almost always the COP.

 

[Yupster Dog]

90% of the time, its the COP.

Also inspect the wire harness for the coil.

 

[doubleaughtEB]

Bought some cops today (hope I never have to say that again) only four and look like AM. Opposed to what's on the truck that do show motor craft. Still at 8 mpg or less before changing. I heard the thermostat can cause this as well.. ?

 

[jr1under]

Bought some cops today (hope I never have to say that again) only four and look like AM. Opposed to what's on the truck that do show motor craft. Still at 8 mpg or less before changing. I heard the thermostat can cause this as well.. ?

Newer COP's have only a part # on the top, older ones have a yellow label with a prominent Motorcraft logo. I'm not at all averse to cheaper parts but have learned never to use aftermarket coils. What MesaGuy said.