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Old 06-24-2009, 11:21 AM   #1
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Default Plug wires popping off/misfire

So I've got a 1997 F150 XLT, 4.6l V8 w/140,000 miles. I've drive it 70+ miles a day, and I've had a recurring missfire problem. The spark plug boots pop off regulary. No matter how hard I push them down on the plug, they still work themselves back off. It used to be random, that is, any one of the boots would jump off, but now it seems to just be cylinder 3. I changed the coil pack some time ago, and just did the plugs and wires last weekend thinking it was just a bad set of wires. NOPE- on my way to work this morning the number 3 started missfiring; I pulled it over and sure as you-know-what the plug boot was not secure. HELP! This is driving me friggen nuts! I'm a decent mechanic, so I'm not totally lame when it comes to maintaining this truck, but this one has me stumped.
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Old 06-24-2009, 12:43 PM   #2
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hmm what brand of wires you running on the truck? i know this sounds stupid but it sounds to me like a defective plug wire set. i figure if the boots wont stay put theres probably a problem with the way they seal. i would try a new set, maybe something original equipment (motorcraft). good luck keep us posted.
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Old 06-24-2009, 01:03 PM   #3
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Default plug wires

Yeah, that was what I originally thought, so I changed the wires last Friday. I bought the high-end brand NAPA recommended (can't recall the name off hand,) as well as premium spark plugs. I thought about crimping the plug connector to see if that will keep it in place. This is really frustrating.
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Old 06-24-2009, 02:13 PM   #4
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yea that would be worth a try man. give each connector a little crimp and see if that helps them snap onto the plugs harder.
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Old 11-18-2009, 11:06 AM   #5
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have same truck #3 plug wire would not stay on but car quest wires are working
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Old 11-18-2009, 05:39 PM   #6
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Konichiwa Jefferysan,
Strange problem....but crimping the wire should work. Only other "far out" thought would be if the plug is not sealing at the head. The plug wires make a pretty good seal in the plug" well". If plugs were changed and sealin surface of plug/ head were not cleaned well. you could have pressure build up in plug "well". This is a real onlg shot, but I cannot think of anything else other than the obvious
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Old 11-18-2009, 09:14 PM   #7
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Default Truck

97 XLT 4.6L 150K miles. No problems with plug wires staying on, had them changed back at 100K and pretty sure they used NAPA wires. No suggestions on your problem other than maybe check around the plug opening for dents or bowing.
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Old 11-18-2009, 09:53 PM   #8
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Default Plug wires popping off

I had the same problem with my 97 F150.
1. Your plug is not threaded down all the way and you are getting blow-by. Check by putting your finger on flat top of plug boot while engine running - You will feel it pulsing - That's blow-by past the plug and its forcing your sealed plug wire off.
2. The few threads that hold the plug are stripped and you are getting blow by. Eventually you will blow a plug right out and it will require you take the heads off and get inserts put in to accept the plug. - Thats a common Ford flaw. I have wondered if heat resistant Loctite would suffice if threads aren't totally stripped out.
3. The hot blow-by can force its way out the side of your spark plug boot and cause a spark arc grounding on your block.

Last edited by kelownaF150; 11-18-2009 at 09:57 PM.
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Old 11-19-2009, 01:05 AM   #9
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Default Boots popping off plugs

Quote:
Originally Posted by Jeffreysan View Post
So I've got a 1997 F150 XLT, 4.6l V8 w/140,000 miles. I've drive it 70+ miles a day, and I've had a recurring missfire problem. The spark plug boots pop off regulary. No matter how hard I push them down on the plug, they still work themselves back off. It used to be random, that is, any one of the boots would jump off, but now it seems to just be cylinder 3. I changed the coil pack some time ago, and just did the plugs and wires last weekend thinking it was just a bad set of wires. NOPE- on my way to work this morning the number 3 started missfiring; I pulled it over and sure as you-know-what the plug boot was not secure. HELP! This is driving me friggen nuts! I'm a decent mechanic, so I'm not totally lame when it comes to maintaining this truck, but this one has me stumped.
I had the same problem with plug boot popping off.

Ford has a problem with the spark plugs stripping out. They blame it on over torquing but it happens on vehicles that have factory installed plugs. Worst case scenario they eject and have caused hood fires.

My guess is that the plugs have backed out and/or the threads are stripped allowing blow-by which builds up pressure and pops the boots off. It can also split the boot causing spark arc.

If you change your plugs and find some have seized, back them out just a little, spray in anti seize, leave overnight. Also back them out and in a little, then out more and so on to help clear the threads as you remove them....I have considered applying Loctite to the plug threads to seal them off.

I'd like to know the rocket scientist that designed that motor. They place it so far back in the engine space its impossible to work on the two back plugs. Just 3" ahead is all it needs.

Mine has 190K and what I saved in maintenance I have spent on fuel.

BTW I am chasing a miss fire as well...It's so much fun changing the wires which are buried...Not!

Last edited by kelownaF150; 11-19-2009 at 01:11 AM.
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Old 11-19-2009, 01:31 PM   #10
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I changed the plug wires again, this time checking the security of the boot on the plug before installing it, and it locked down snug. I believe the root of this problem lays with the design of the NAPA plug wires, but may also include factors discussed in this thread. The new wires (I think I got them at Schuck's) had a smaller overall diameter, and allowed me to twist and work the boot down further on the plug. It seems that the bigger boots on the NAPA plugs were getting hung up on the lip of the plug access, thus not getting a good seat and working off. Since changing to the slightly smaller boots a few months back, I've not had this happen again. Finger's crossed.
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Old 11-19-2009, 01:31 PM
 
 
 
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