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Discussion Starter #21
New Motorcraft upper & lower O2's 2 years ago (maintenance).

Yes, new fuel filter 2 days ago with the new fuel pump.

As far as the money, everything I replaced was "out of spec" via testing, so I don't feel bad yet. We were planning on keeping this SUV for another year anyways.
 

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Discussion Starter #23
I cleaned the mass airflow sensor & the other sensor in the air cleaner intake tube yesterday. I unplugged the EGR valve & still this hesitation persists.

I also unplugged one injector at a time while at idle & they were all doing their job.

So then I began to pull out each spark plug for inspection. Cylinder #4, the terrible right rear, looked horrible on the outside! It looked corroded & nasty looking, nasty water was present. I also noticed this Motorcraft plug was a different PN# than what I had installed 4 yrs back.

It was a Motorcraft platinum 32 instead of a 22. It brought back a memory from 3 yrs ago when my wife worked out if town. My father & I had to close-off the failing front heater core back then. She had to have her SUV towed into the town where she USED to work. Apparently the shop replaced that rear spark plug with a non-matching one (due to a leaking heater hose clamp we had installed). Coolant had fouled out this same cylinder then.

As I said, I inspected this spark plug last & then cleaned & dried everything out last night. I used a good coating of dielectric grease today inside this spark plug boot- Just like I had done 4 yrs ago & something this auto shop failed to do 3 yrs ago on their repair.

I test drove my wife's SUV today & this miss/hesitation is now completely gone!!
 

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that's surprising... I would have thought that you would have gotten a missfire code.
 
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I've seen spark plugs "ground out" and misfire because of excessive oil leak from valve cover burns and builds a "bridge to ground," or fills a recessed plug like you had.
 
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