Miss at idle on 2010 4.6 3valve motor

Speedracer67 · May 4, 2022

Had a check engine light and miss. Checked code and it was misfire on cylinder #2.
182,000 miles.
Changed all plugs, with no problems and #2 coil pak.
Now have a miss at idle, clears up above about 1000 RPM.
No check engine light, engine runs good on the road.
Any ideas??
TIA
Rick

Dino Dino Bambino · May 5, 2022

You might still have a pending code so it might appear if you wait long enough.
Did you apply nickel anti-seize to the barrel of the plugs where they meet the head (not the threads)? It's possible you might have accidentally contaminated one of the electrodes.

86GT351 · May 5, 2022

What plugs did you use? Are they properly gapped? Always check plug gap.

Ekis · May 5, 2022

Dirty injector?

Speedracer67 · May 5, 2022

Motorcraft plugs, didn't need gaping. Don't think I got lube on tip of plug.
Do have original injectors but I was hoping to get a code.
Will post what I find out
Thanks

Laga · May 5, 2022

I’ve had a brand new Motorcraft plug go bad after a week. Never threw a code but wasn’t firing. You might have a bad one.

Speedracer67 · May 5, 2022

What brand plugs do you think might be better?
I hate to pull all 8 plugs to see which one might be bad.

Dino Dino Bambino · May 6, 2022

After 100 miles of driving you'll either get another code or, if it's just a fouled up plug, it'll clear up.

Speedracer67 said:
What brand plugs do you think might be better?
I hate to pull all 8 plugs to see which one might be bad.

You already have the best plugs for your application. Luckily yours is a 2010 model so you don't have to worry about breaking any plugs upon removal, so it might be worth your while doing so to find out if any of them looks different from the others.

86GT351 · May 6, 2022

Speedracer67 said:
Motorcraft plugs, didn't need gaping. Don't think I got lube on tip of plug.
Do have original injectors but I was hoping to get a code.
Will post what I find out
Thanks

But did you check the gap?

Speedracer67 · May 6, 2022

No I didn't. Gap looked the same on each plug. How would you change it? Bend the loop on the bottom?

86GT351 · May 6, 2022

Speedracer67 said:
No I didn't. Gap looked the same on each plug. How would you change it? Bend the loop on the bottom?

Yes. Always check gap. Could be a few thousandths off creating your issue. That might be why you have the issue and it smooths out under load.

07 Boss · May 8, 2022

Speedracer67 said:
No I didn't. Gap looked the same on each plug. How would you change it? Bend the loop on the bottom?

If you have the stirrup style strap on your plugs there is a tool you can get for gapping. I use a different style plug but when I ran HT0s I would take them down to my local modular garage and tell them what gap I wanted and tossed the guy a double sawbuck.

Pentalab · May 9, 2022

On my 2010 GT, the oem gap is 1.5mm / .060". Since I have a small roush M90 blower, the gap is reduced to just .035" (5.7 psi boost). I replaced the plugs years ago, with Brisk silver plugs, and gapped to .035". If no blower involved, the gap is set to .060" / 1.5mm.

Dunno what the gap is on plugs...right out of the box. They all looked identical, but were not .060".

07 Boss · May 9, 2022

Pentalab said:
On my 2010 GT, the oem gap is 1.5mm / .060". Since I have a small roush M90 blower, the gap is reduced to just .035" (5.7 psi boost). I replaced the plugs years ago, with Brisk silver plugs, and gapped to .035". If no blower involved, the gap is set to .060" / 1.5mm.

Dunno what the gap is on plugs...right out of the box. They all looked identical, but were not .060".

I've been running my blower for so long I don't remember the stock plug gap but that seems awfully big. I can't imagine it being much bigger than .045 or so.

Pentalab · May 9, 2022

07 Boss said:
I've been running my blower for so long I don't remember the stock plug gap but that seems awfully big. I can't imagine it being much bigger than .045 or so.

Manual sez .060" or 1.5mm. Blower went in just a few months after I bought the car, so it's been .035" ever since.

Sammy70 · May 10, 2022

Speedracer67 said:
Now have a miss at idle, clears up above about 1000 RPM.
No check engine light, engine runs good on the road.
Any ideas??
TIA
Rick

Unplug injectors one at time while engine is idling and listen for a change in rpm.

If one cylinder has no change you'll know the problem cylinder and can go on to check each component--plug, coil, injector, etc.

I've changed literally hundreds of 3v spark plugs and have seen the occasional dead plug right out of the box.

Speedracer67 · May 10, 2022

Sounds like a good plan. Still no check engine light but miss is still there.
Will report back.
Thanks

skwerl · May 11, 2022

My 5.4 3v has a tap at idle that instantly clears up with a little throttle and runs awesome. My mechanic said it was the phaser not getting enough oil at idle. I already upgraded my oil pump so the next step is thicker oil.

Miss at idle on 2010 4.6 3valve motor

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