Solved my sluggish performance problem

[DanL]

Haven't posted here in ages but thought I'd share something interesting I discovered today. My wife's owned her '04 Pilot since late 2003 and it's been pretty much trouble free the whole time. But over the last year or so it started become quite sluggish. I checked all of the normal things -- replaced the EGR valve, cleaned out the carbon from the tracks in the intake manifold, etc. but nothing seemed to fix it. Today I decided to change the plugs even though they're not due to be changed for another 20K miles or so (the Pilot has 85K miles on it). The plugs were in fine condition but guess what? Three of the six were loose (two in one bank, one in the other)! I've never heard of that happening before. I replaced them anyway (took 30 minutes total) and then when out for a spin. I'm happy to report that the old Pilot is back! Nice, smooth acceleration just like when it was new. So what would cause plugs to loosen like that?

[macphanatic]

My guess is thermal expansion and contraction of the heads and spark plugs.

[DanL]

Originally Posted by macphanatic

My guess is thermal expansion and contraction of the heads and spark plugs.

Perhaps you're right since we're talking about steel plugs in an aluminum head. It sounds like a plug torque check is in order well before the replacement interval. Would have really sucked if one of the plugs blew out of the head, taking the threads with it. Well worth the 15 minutes it takes to check IMO.

[theirishscion]

Originally Posted by DanL

I've never heard of that happening before.

Alas, whilst you may not have heard of it before, you're not alone;
Melted Ignition Coil
Anyone ever hear of spark plugs backing out?
Melted coil pack and broken spark plug!!

This seems to be an ongoing problem with the Accord and Odyssey (and presumably MDX etc etc as well)

It's my current position (personally at least) to either re-torque or better yet replace plugs at 50,000 or thereabouts, rather than the official 105,000. Aside from catching a loosening plug early and saving coil-packs, cylinder head threads and worst-case-scenario actual cylinder wall damage, replacement should also guard against the plugs welding themselves into the heads over 105,000 miles, which they have a bit of a reputation for.

I gather there is also real value in using the factory NGK plugs, in that they have a plated coating on the threads which acts as protection against galvanic corrosion between the steel plug and the aluminium head. Allegedly, said corrosion can seriously exacerbate the aforementioned welding-into-head effect. I haven't looked into this claim in any great depth, I just present it for consideration. If anyone else would care to chime in here, I'd be very interested to hear their thoughts.

[whizmo]

Yes, this is not the first instance of spark plugs being reported loose. I think a 50K plug replacement is probably something that would be good preventative maintenance and might even return the cost in better fuel mileage.

- Mark

[rocky]

I waited until 105k before replacing the plugs. Had the tb done a couple of weeks later. However just replacing the plugs resulted in much better and smoother performance. So you might be right about shorter intervals

[theirishscion]

Originally Posted by rocky

I waited until 105k before replacing the plugs. Had the th done a couple of weeks later. However just replacing the plugs resulted in much better and smoother performance. So you might be right about shorter intervals

Assuming you wrenched 'em yourself, how hard were they to break loose? Did they all seem relatively similarly tight? Of course, your engine doesn't sport VCM either, does it? I'm a bit suspicious that the temperature cycling inherent in the VCM system may coax the plugs into backing out under certain unfavorable circumstances. Of course, Honda probably thought of that, which is why it has the same system periodically coats them in engine oil to force an early change, thereby nipping the problem in the bud.

[rocky]

05s VCM free and proud of it. They came out easy without a fight

[theirishscion]

Originally Posted by rocky

05s VCM free and proud of it. They came out easy without a fight

I really think I'd be ok with the fuel efficiency penalty associated with a de-tuned (to run on regular gas) version of the MDX's 3.7L V6 in exchange for a bit more low end torque and responsiveness (and proper VTEC.) Sadly, the market seems to say no.

Actually, correction; if Acura would just sell something Pilot sized, not just based on the same platform like the MDX, I think I'd be fine with paying the Acura premium to drive that instead.