I have a 2000 Legacy L wagon that I just did a plug and wire change a month or two ago. Over the last month the #1 plug wire keeps popping off the plug. I've put my weight into putting it back on and know that there is no way that it's shaking lose. I pulled the plug yesterday to check for damage and found no damage to the plug. I'm getting a knock sensor obd2 code before the plug pops of and then a misfire code when it does come off. Any thoughts?

What brand of plug wires did you use?  Some of the cheaper ones are just that, cheap, and have issues.  

Denso wires and NGK Irridium plugs

Have you tried swapping the wire with #3 and seeing if the problem persists?  That will eliminate the wire being the cause of the problem.  It could be you caught a wire with a lose cap it in as well.

Have you tried swapping the wire with #3 and seeing if the problem persists? That will eliminate the wire being the cause of the problem. It could be you caught a wire with a lose cap it in as well.

No I haven't. Just know that after I press it back in its nice and snug and takes a bit of force to pull it out.

That means the boot is tight, not the metal part that hooks to the spark plug.  If it's lose and arcing the arcing could be  creating enough force to push that boot off.

sounds like a compromised wire.

 

swap wires between cylinders.

Replace the wire. Sounds like you bent the internal clip or it's damaged, and it's not seating around the plug tip firmly or was crooked while you were trying to force it and bent, thus only touching tip of plug and falling off from engine movement, vibrations, etc. It should FIRMLY go around the plug tip, not just rest on it.  Also, the wire that carries the electrical signal is basically folded under the crimping of the clip. If the wire is damaged, you won't get a signal.

 

Take car back to where you bought the wires, take wire in and explain it's "defective" and ask for a replacement. They should open a new box and give you one. This time, while installing, add a tiny amount of boot grease. Then, make SURE it's centered while attaching. You should never have to "force' it on. If it's crooked in the boot, it'll bend easily and never seat correctly. With the grease, it should just slip on and "click'. 

 

After replacing, disconnect the (-) NEG battery terminal for roughly 30 seconds (seems to reset instantly but 30 seconds is a safer bet) then reconnect and make sure both battery terminals are tight less you want charging issues later on. Go drive car. Issue should be fixed.

 

If it somehow pulls off again, look at how you routed thew wire. 

Edited July 7, 201510 yr by Bushwick

Replace the wire. Sounds like you bent the internal clip or it's damaged, and it's not seating around the plug tip firmly or was crooked while you were trying to force it and bent, thus only touching tip of plug and falling off from engine movement, vibrations, etc. It should FIRMLY go around the plug tip, not just rest on it. Also, the wire that carries the electrical signal is basically folded under the crimping of the clip. If the wire is damaged, you won't get a signal.

 

Take car back to where you bought the wires, take wire in and explain it's "defective" and ask for a replacement. They should open a new box and give you one. This time, while installing, add a tiny amount of boot grease. Then, make SURE it's centered while attaching. You should never have to "force' it on. If it's crooked in the boot, it'll bend easily and never seat correctly. With the grease, it should just slip on and "click'.

 

After replacing, disconnect the (-) NEG battery terminal for roughly 30 seconds (seems to reset instantly but 30 seconds is a safer bet) then reconnect and make sure both battery terminals are tight less you want charging issues later on. Go drive car. Issue should be fixed.

 

If it somehow pulls off again, look at how you routed thew wire.

Just went back to advance and did that. Used dielectric greese.

Am I disconnecting the battery to clear code? If so my obd2 scanner can do that.

After comparing the two in the store seems like the metal bout inside wire was folded in upon itself.

that's what i was thinking - they can get crimped and damaged. 

Yeah, just reset battery so ECM goes back to a day 1 state. The misfire will be stored and it's always best reset after fixing a major issue.

 

Had a feeling it was the clip. They can float around inside the boot, and if you force it while it's off center, it'll bend. The grease helps keep moisture out, makes for a solid electrical connection, and makes it easier to remove the boot in the future if need be.

 

Glad it's running proper now. Might take a little while to run 100% again due to the misfire as raw gas probably got dumped into exhaust. Run it good for awhile.