'08 Civic R18 Spark Plugs 103,265 Miles

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Site Donor 2023
Jan 9, 2009
New England
The maintenance minder has not indicated that the spark plugs need to be changed, but I've had the plugs since right around 100k and figured it was an easy way to determine if this was the cause of some of my hard-starts. Information: Car: 2008 Civic LX Miles: 103265 (purchased @ ~60k miles) Plugs: IZFR6K-11S (Ir) Miles on Plugs: 103265 - The PO kept very good records and because he was not mechanically inclined, took it to the dealer for EVERYTHING. There was no record of spark plug change. Issue: Car will take longer to crank before catching, and when it does catch, it will sometimes stumble for a second. Placing the key in ON (without starting the car) for a few seconds seems to help, and cycling the key OFF and then ON a second time provides no discernible change. While changing the plugs I added a dab of dielectric grease to not only the spark plug terminal, but also the coil connection. For good measure, I disconnected and reconnected every connector accessible from the top in the engine compartment. There were no visible signs of corrosion, but I figured it would be a good measure to take. This also stems from some trouble-shooting resolution being as simple as removing and reseating a card to fix sporadic faults. Finally, electrically, I cleaned the battery terminals and re-applied dielectric grease before restoring the battery. This reset the ECM in the process... Other Other: Just after I had the car dropped off at the dealer to update the TCM (read about an update online that fixes minor shifting issues, which we've been experiencing) and check for ECM updates. The dealer found and installed an TCM update: NAA670 I can't be sure if its simply a placebo effect, but with the above done, the car seems to start better and shift better. A lot of variables, I know. And while the spark plugs shown below all are within their spec'd gap and look fine, who's to say whether they were performing at 100% or if their performance was much more degraded than appearances would lead me to believe. So, here are the pictures, open for comment. Cylinder 1: Cylinder 2: Cylinder 3: Cylinder 4:
It's not placebo effect at all. I changed the plugs on my focus recently and had no problem climbing some hills again; even foot to the floor, I'd lose speed with my foot to the floor in 5th gear. After the plug change, I was able to maintain speed at part throttle in 5th gear.
Plugs look good for that mileage. The issue with starting is probably because the plug gap is 3X what it was originally. My Tacoma with iridium plugs, the gap was 4X original at 70K, but it is subject to a lot of towing. But it still ran fine.
Several vehicles I've owned have exhibited the same improvement with new plugs. On our Jeep, 30k is the magic number.
I only had the car for a few days after the plug change, but one thing I noticed, is that the transmission doesn't seem to shift as frequently or as much for the same hills I drive up every day. I'm not sure if it's the transmission control module update or the plugs that are responsible, but taking the hill right before my house on my way home at the same speed as always, the transmission only down-shifted once to a higher lower gear, instead of twice, to maintain speed. This engine, with the economy v-tec, is also pretty gutless at low RPM and part throttle, but I believe I'm noticing a much better part-throttle response. On the highway, with no traffic to annoy, I keep the cruise off and try to maintain speed as much as possible without letting the transmission shift for minor hills. I feel that this is possible now, whereas the speed would dip too low and cause a shift before the change, even if I sped up a little in anticipation of the upcoming hill. I know all of the above is anecdotal and not really valid data, so take it for what it's worth. Also keep in mind that the TCM update could have had a major affect on shift behavior as well as quality, so the only real evidence for improvement not attributable to the update is probably the starting behavior, which my wife, who drives it daily, commented that it's much improved. We used her car to run errands over the weekend (better on gas than the Subie) and it started up immediately each time, which was rare before, at least on cold-starts. So, if you're having similar issues in your R18 Civic, then I'd definitely suggest: 1. Transmission shift quality: go see the dealer about an update, if you haven't ever had your TCM checked for one. 2. Start quality: check connections and change your plugs, if you have the means to do so easily (i.e., can do it yourself for cheap.)
Also as the spark plug gap get bigger the easier it is for the spark to take the easiest path to ground.
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