What is this "knocking"?

We have a 2002 Explorer XLT with 8 cylinder enging, rear wheel drive only, 53000 miles.
Have always had it serviced by the dealer.
Some time ago it started "missing" or what ever it is. This is
very erratic. Seems to happen most when doing 40 - 50 mph and I slightly push on the gas pedal. It even happens with the cruise control on and we start up a hill or bridge, etc.
I can "stomp" on it and nothing strange happens.
I have asked the dealer to check it out.
They did some "tests" and "reset the PCM". Six or so days later it was back to the same old thing.
I did discover that putting a container of Techron in the tank just before filling up completely stops this problem.
Chevron gas which contains Techron does not stop it.
I mentioned cleaning the injectors or replacing the spark plug wires. They weren't interested in eith
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On Fri, 22 Feb 2008 16:22:54 -0500, "wlwallick"

What you have may not be a misfire. At the speed range you state, it may be transmission torque converter shudder although that should be rare with the transmission updates and a change to synthetic fluid for that vintage. Have you had the transmission serviced in cluding draining the converter. I suspect you may be well beyond the recommended interval if you have not had this service done.
Another problem IIRC, may be a bad coil. IIRC, your has the coil-on-plug where there is an ignition coil on each spark plug. I believe there have been some problems with water getting into the boots of some causing a short and misfires on #3 or 4 cylinders. Don't recall for sure but, I believe the cure was a now coil and boot for that cylinder. You may want to check for a service bulletin on it. If that doesn't do it, you probably need a personal touch on it by a good technician. Keep in mind that something like this is hit and miss on the diagnosis if it won't do it while the tech is working with it. Every once in a great while, you will find the guy who had this exact problem a couple of times and knows what to look for up front.
Lugnut
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On 2/22/2008 8:29:19 PM, lugnut wrote:

wheel
later
recommended
At 30000 miles they did a transmission flush and replaced the fluid. This is part of their usual maintainance. The problem developed much later.
A coil on each spark plug? Good grief.
WLW
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Then you have a fuel related problem. The additive is either bringing your fuel up to spec or compensating for some problem in the fuel system.. My first plan would be to change where you buy your fuel. Buy it from somewhere with a high turnover and see how it goes after a few tanks.
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On 2/23/2008 4:34:10 AM, "RustY" wrote:

bringing your

system.. My

from
few tanks.

I have changed stations, even put "hi test" in - no help.
Something that has concerned me is possible water in the tank.
Here in Florida, after the hurricanes, there was water in just about all the gas. Of course that was several years ago.
On the other hand, the air is usually very humid and I have wondered if that humidity in the tank would condense after we put the car in the garage where it is usually cooler. Thus water in the tank. "Grasping at straws"?
WLW
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Try a higher octane gas. If that works then the ignition timing may have to be adjusted.
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DID YOU LET THE OIL RUN DRY??!!

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On 2/24/2008 1:17:36 AM, "Eddie S." wrote:

NOT YET!!!
We have always had the oil changed every 3000 miles. Never been down much less out.

wheel
the
later
plug
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