Please Help With Boost Mis-Fire

jonroe

Registered User
In a related post called "VA Smog Saga - Conclusion" I explained my last 3 weeks of frustrating smog testing.

The result, aside from finally passing, was a bad mis-fire under hard boost that just developed during the last week of cat replacement and smog testing.

I have a hard (what seems to be) spark plug miss on 1 or 2 cylinders when getting into boost above about 4psi. It seems to run strong without any miss below boost and up to about 3-4psi.

Where do I start looking? Could it be a fouled plug from emissions cleaners?

I'm very frustrated.

Thanks for listening.

Jon
 
Plugs and wires..

Either one is bad, both are bad, or some of the wire boots are coming off of the plugs.

Make sure if you replace the plugs to use oem plugs, or Denso or NGK iridium plugs
 
Thanks.

I'm pretty sure the wires are good. They are OEM Motorcraft just new last December. I've looked for loose ends - don't see any. Also, plugs are near new OEM Motorcraft but could have been fouled recently.

I'm hoping this symptom doesn't point anywhere else.

Jon
 
Yah, I had the same problem and all of the boots on mine seemed secure also. I got in there real close though and pushed on them nice and good and I guess one of them must have been mis-seated because the problem disappeared
 
Revisit - Please Help

Sorry for popping this up again but I'm still seeking helpful input on this problem.

It has not "cleared itself" during the last couple of weeks of normal (not high boost) driving and still misses very hard at above 4psi boost buts runs clean under that.

I'm ready to switch out plugs but afraid that's not it. The miss is very hard (almost like several cylinders dying) that you can't "drive through". It's not like pushing an engine hard and having only one missing plug which you can "drive through". My condition forces you to back off immediately and almost feels like backfiring. Also, the boost needles swings around during the miss in a strange way.

Please..........any suggestions beyond plugs? That's seems too easy. I fear a more sinister problem.

Thanks.

Jon
 
I had the same fears and sure enough it was plugs and wires even when I had new Magnacore wires and Motorcraft plugs. I know it may seem silly but that is almost certainly the cause.
 
Gosh, I SURE hope you're right.

These complicated beasts give you nightmares. It's not like the good old days when I did all my own work on my 1970 TBird with the 429 V8! Now, that was fun and that was a kickass motor.

Jon
 
Update Boost Mis-Fire

Problem Solved.

I bought 6 new Autolite APP 2544 plugs and had my mechanic work on it yesterday. I asked him to just do the "easy" side (driver's) first and try it out since the passenger's side is now even harder than usual because of my new MAC cold air intake which is not as easy to take on and off as the stock piping.

So, he changed the 3 plugs on the left side and the mis-fire under hard boost is gone. So, it really was one of those fairly new (6000 miles) plugs that was bad.

The possibly not-so-good news is that when he showed me the 3 old plugs we noticed that plugs 5 and 6 had a dull orange-red color on the side electrode. He said this could be an early sign of head gasket leakage around number 6. He suspects leakage at the back of 6 on the edge of the head and said that a similar condition could exist on the front of number 1 as well because he has seen these edges of the head as weak points. There are no other signs of HG problems that I have seen yet.

So, I don't know what to think other than that I will be keeping a very sharp eye out for further indications before checking her into the hospital for major surgery.

The other thing I thought of is maybe that there is a dusting of rust on these due to the fact that I don't run it every day anymore but usually only a couple times a week so the cylinder sits for days at a time.

Oh well, it runs good now!

Jon
 
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