ominousnimbus

New to the forum here -- I'm not an enthusiast, but simply a 2005 LX sedan owner who recently wanted to save a few bucks by changing the plugs myself. I am approaching 110k miles, so it was listed as standard maintenance in the owners manual.

The OEM plugs were NKG Iridium, while the plugs I bought at Advanced Auto Parts were Denso Platinum TT.

The results were not what I expected: instead of increased performance, I got a very noticeable drop in mileage, more hesitation, and more struggling at highway speeds. To be specific, I'd always gotten 36-38 mpg highway right up until the change, while I've seen 30-32 mpg since. I'm 100% sure that the change was abrupt and occurred right after the plug change, since I always try to calculate MPG when I fuel up.

First of all, is it possible that using plugs with a 0.040 in. gap instead of the OEM 0.044 in. could be the cause of all my problems? If so, I'll just head back to the store and pick up something that meets specs exactly. (I saw several reviews claiming the Denso's were OEM on some 7th Gens, and that anything in the range of 0.039-0.044 was acceptable, so I didn't think it was a problem -- they are 75% cheaper than the Iridums, after all).

If that's unlikely, then what else is most likely that I screwed up? If there's a problem with one of the plugs, is there any easy way to tell which one it is?

04 Honda Civic

iTrader: (2)

Buy OEM plugs from the dealer. Your problems will go away. DO NOT GAP THE ONES YOU GET FROM THE DEALER.

They use Irridiums. If you buy anything else you will get the rsults your experiencing.

ominousnimbus

When I changed the plugs a couple months back, the OEMs that I pulled out were NGK PZFR6F-11 (Laser Platinum Premium). I picked up a box of those tonight for a cool $45.00 at O'Reilly -- nearly four times the Denso Platinum TT that I have in right now. Will make the swap tomorrow, and cross my fingers that everything goes back to normal.

BTW, I did not gap the set I have in now, nor do I plan to do so with the NGKs. My main question was whether or not the (pre-gapped) 0.040" plugs could actually cause problems if the originals were only 10% different, at 0.044".

em2maxamillian

I agree with 04_Honda_Civic, replace the plugs with the same OEM plugs. I tried NGK and the car gave problems, particularly when I went to go and start the thing. I went back and got the OEM Denso plugs and it runs well now. Get about high 20's to low 30's MPG, but I live in a city with lots of stop and go driving, so that's pretty good. The only difference is I got the platinum versions of the Densos, not the iridiums that originally came with the car.

maxtierney

iTrader: (5)

Your problem is mainly the gap size. Simply stated, that 10 percent difference will result in a spark that's shorter in duration, and smaller/weaker than stock. This causes an inefficient/incomplete burn.

Harder starting, increased emissions, more fuel consumption, bad fuel economy, etc., is the end result. Unless you are tuning, modded or boosted, it's best to leave the gap alone.

ominousnimbus

OEM style plugs are now in. Will have to wait until the next time I'm on the interstate for an extended period to verify mileage has returned to normal, since it was only highway mileage that dropped noticeably.

After completing the job, I noticed something disconcerting about the Denso plugs I installed a few months ago: one of the four (the leftmost in the pic) appears to have very little wear, compared to the others. Any ideas what this might indicate? I'm hoping just a bad or incorrectly-installed plug, and not something like cross-threading or worse. These plugs were in service for approximately 5-6,000 miles.

ezone

What on earth are you looking at to determine this "wear" you speak of?
All I see on the far left plug is the backside of the ground electrode.

ominousnimbus

The other three have a brownish/burnt area on the lower portion of the white ceramic near where it meets the metal (immediately below "PK20TT"), while the left plug has virtually none.

ezone

What you are looking at is completely irrelevant.

04 Honda Civic

iTrader: (2)

lol ^^

Part numbers for spark plugs are as follows:

Any other plug and your just taking a gamble on how the car will run (Dont ask me how I know..)

NGK: PZFR6F-11 (This is what you pulled out OEM plug)

However you can also use

DENSO: PKJ20CR-M11

04 Honda Civic

iTrader: (2)

This is true, you want the correct gap. You dont want to be off at ALL.

You need Irridium plugs, but you really are not supposed to gap irridium plugs.
How is this possible you ask?

Auto parts stores that sell Irridiums are pre gapped, and unless you buy the EXACT plug for your car the gap will be off.

Best to just bend over to the dealer. They arent that overpriced if you get them at the right dealer, think I paid around $60 for mine. May seem like alot but you only change them every 110k miles so you might as well do it right.

But if you can find the EXACT same ones at the local auto parts store better for you. (I couldnt find the DENSO's I wanted)

ominousnimbus

So, since starting this thread I have:

- Put in new OEM plugs identical to the ones I drove my first 110k with (NGK Platinum).
- Timing belt and water pump replaced (standard maintenance).
- Dealer claimed cam/crank shaft seals were leaking while changing out the belt, so replaced those.
- Replaced battery (was time after ~4 years).
- Used half a bottle of Redline SI-1 a few fillups ago.

Yesterday I did a long drive that was nearly all on the highway. At fillups (each about 6-8 gal, or just over half the tank), I recorded 32, 33, and 31 mpg. This is unquestionably lower than I consistently saw for the first five years I owned this car. I would *always* get 35-38 mpg on pure highway trips, with maybe the rogue 34 mpg when facing a strong headwind or something, which wasn't the case yesterday.

In particular, the last tank bothered me because it was done entirely on cruise control at 75 mph: 243 mi / 7.81 gal = 31.1 mpg. That exact same driving scenario (cruise at 75 mph) would guarantee me 36 mpg every time up until recently.

I believe my idle is now noticeably rougher than before this drop happened, as well.

Now that the plugs are OEM again, they've been ruled out as the direct culprit. Still, this drop in fuel economy seemed to happen quite suddenly right around the time I did the first plug change back in December. I just can't figure out what the causal link would be, and maybe there isn't one and it's pure coincidence. Either way, though, it happened too abruptly for this to be a case of "the car's just getting old."

- I don't have any extra weight in my car that I didn't before.
- I'm not using different-quality gas than I was before (have always gone with the cheapest, for better or worse).
- I haven't seen the check engine light at all since this problem started.

Given how much highway driving I plan on doing in the coming months, I'd REALLY like to figure this out ASAP.

ezone

At what point was the poor fuel economy really noticed, and was there any other associated work done immediately prior to this?
Is there a lack of power or response?
Tire sizes, changed tires, etc?
Tires aired up?
Brakes not dragging?

Are you in an area that uses oxygenated fuel, MTBE, or other pollution reduction methods in the fuel? Those can cost you mileage.

Word up: http://www.toptiergas.com/

It would be interesting to check a few datasets on a good scanner while driving, and maybe do a few diagnostic moves while watching the data for changes, or monitoring fuel efficiency. And check the fuel pressure.
Maybe even comparing its data to a known good car could be beneficial.
The average user doesn't have access to this stuff, and the average parts replacing mechanics won't know what to do with it either.

ominousnimbus

It was within a few weeks after my initial attempt to change the plugs. It definitely was not a gradual decline over 6 mo. or a year or anything like that. In fact, I drove across several states in December, changed the plugs while visiting relatives over the holidays, and then saw the reduced mileage on the way home. There was no other work done on the vehicle for at least 6 mo. beforehand, other than oil changes at the dealership.

While trying to install the first new plug, I had a lot of trouble with the spark plug socket coming off the ratchet extension while down in the hole. This resulted in the other plugs and ignition coils being out for probably half an hour until I wised up and duct taped the extension to the socket. I assume it's not possible that dirt or other contaminants getting in during that time could be at fault? Also wonder if I could have somehow damaged one of the coils, since they're the only parts I touched besides the plugs themselves. (Still, as I said earlier, I haven't seen the check engine light at all).

It seems to struggle a bit more at high speeds and going uphill, and idle is rougher (some mild shaking). I also notice a very faint "whirring" noise sometimes that starts when accelerating past 50-60 mph.

Tires were changed about a year ago (well before problem started), and are inflated to just over spec (~33 psi) as I've kept them all along. Have double-checked psi repeatedly over the past couple months to rule that out.

Not that I'm aware of.

Not sure, but I've lived in the same location for the entire life of the vehicle and have been using the same stations for the most part. Using a myriad of different gas stations, I consistently saw 35-38 mpg highway from 2007 to Dec 2011, and then suddenly 30-33 highway since then.

ezone

While trying to install the first new plug, I had a lot of trouble with the spark plug socket coming off the ratchet extension while down in the hole.
They make extensions that lock to the socket. Handy little buggers.




This resulted in the other plugs and ignition coils being out for probably half an hour until I wised up and duct taped the extension to the socket. I assume it's not possible that dirt or other contaminants getting in during that time could be at fault?

If dirt got into the cylinders, you could have things like loss of compression and/or oil consumption from scored cylinder walls. Also, there would have to be dirt already in the plug holes to get in the cylinders......unless you did this outside in a sandstorm, I doubt any of this is likely.


Also wonder if I could have somehow damaged one of the coils, since they're the only parts I touched besides the plugs themselves. (Still, as I said earlier, I haven't seen the check engine light at all).

You would have misfires and misfire codes (I hope) if you seriously damaged any of them.

It seems to struggle a bit more at high speeds and going uphill, and idle is rougher (some mild shaking). I also notice a very faint "whirring" noise sometimes that starts when accelerating past 50-60 mph.
Does this "whirring" happen if you sit in the driveway and rev the engine up? Can you pinpoint it with a stethoscope or a length of tubing?

Since you seem to have a real performance issue, this should be relatively easy since this isn't an intermittent problem, this is a constant issue. Your gas mileage dropping off appears to be the RESULT of the poor engine performance issue. Once the engine runs "right" again, the gas mileage should come back.

For the performance part of it, I would probably start with checking cam timing and a few other visual checks that are relatively simple but a little bit time consuming.
Then maybe looking at computer data, then, depending on what that looks like, that may lead me to other testing.
Fuel pressure check
Backpressure check (and/or vacuum check for exhaust restriction)
What is MAP sensor voltage @ idle with no loads?


Have you ever tried screwing the original plugs back in?Has a real shop looked at this car for this problem?
Where are you located?

ominousnimbus

ezone --thanks a ton for your replies. Unfortunately, this is quickly getting above my pay grade, so I will probably take it in to a local shop (the problem has persisted for an additional ~1500 mi. of highway driving over the past couple weeks).

As a last ditch effort to perhaps at least narrow down the list of potential problems and avoid diagnostic fees, a few new developments:

- I borrowed a scanner from AutoZone and was not seeing any codes.

- I measured the resistances for my coils and found they varied by about 3-4%. I'm assuming this is within spec.

- I've noticed a persistent pattern on long drives: gas mileage gets worse over the course of the day. If my car has been sitting unused for a few days, then I get on the interstate, the first tank will be something like 32-33 mpg... then the next might be more like 29-30 mpg. Hesitation and struggling at high speeds seems to get worse, too.

Clearly, there's a whole slew of possible culprits I'll have to have a mechanic check out. But to completely eliminate the simplest and most obvious thing I can think of, since problems started upon changing the plugs... is a 1/4-1/3 turn of the ratchet after hand-tightening appropriate when installing plugs? This is what I had read a couple places. However, I'm noticing that when I go to take them out, they come loose much easier than they did when I took the OEMs out (of course, those had also been in 110k miles...).

ezone

ezone --thanks a ton for your replies. Unfortunately, this is quickly getting above my pay grade, so I will probably take it in to a local shop (the problem has persisted for an additional ~1500 mi. of highway driving over the past couple weeks).

As a last ditch effort to perhaps at least narrow down the list of potential problems and avoid diagnostic fees, a few new developments:

- I borrowed a scanner from AutoZone and was not seeing any codes.

- I measured the resistances for my coils and found they varied by about 3-4%. I'm assuming this is within spec.

Chasing the wrong things. Coils are not your problem.

- I've noticed a persistent pattern on long drives: gas mileage gets worse over the course of the day. If my car has been sitting unused for a few days, then I get on the interstate, the first tank will be something like 32-33 mpg... then the next might be more like 29-30 mpg.

Wow. Multiple tanks of fuel in one day?? Just how much driving do you do in one day?


Hesitation and struggling at high speeds seems to get worse, too.

This sounds like what your complaint should be about. This is most likely what is causing your mileage loss.

Clearly, there's a whole slew of possible culprits I'll have to have a mechanic check out.

Stick to describing the symptoms.
Don't name off parts.




But to completely eliminate the simplest and most obvious thing I can think of, since problems started upon changing the plugs... is a 1/4-1/3 turn of the ratchet after hand-tightening appropriate when installing plugs?

Did you look up torque specs? What did that say?

Maybe this will help clarify for you: http://www.ngksparkplugs.com/tech_su...x.asp?mode=nml

Yours are 14mm and aluminum head.

Get your torque wrench and use the specs listed that fit your engine.

(Now that the gaskets on your plugs have been crushed, you can no longer use the +1/4 turn method of tightening, or whatever that was.)



This is what I had read a couple places.

I forgot. The internet is the Bible.


However, I'm noticing that when I go to take them out, they come loose much easier than they did when I took the OEMs out (of course, those had also been in 110k miles...).

May or may not be relevant. I can't tell from here.


HTH

EdW2007Civic

I have a 2007 Coupe with a 5 speed and have recently seen the same loss in mog. My car has 61,000 miles on it and I've owned the car since late in 07 when I bought it used with 7,000 miles on it. Up until 2 months ago I consistently checked the MPG every time I fill up. On a trip I got as high as 40 mpg almost always 38+ driving 72 mph highway. Around town always got greater than 35mpg. The last several months mpg has dropped off almost instantly to low 30's. I just did some highway driving and got 33 mpg. I have not done anything. Original plugs, used the same gas, tires are good, etc etc.
What is a likely cause?? Could it be loss of compression? May have a little less power than It used to, although it's hard to tell. Have oil and filter changed reqularly, checked oil and it looks clean and up to the full mark. Have not done brakes yet?
Any advice/thoughts before I call the dealer??
Thanks

ezone

SWAG:
Winter fuel blends, wait til after Jun 1 and see.

Use top tier fuel, low octane and low/no ethanol if possible. http://www.toptiergas.com/

Cheapo brand of tires. (We see this sometimes on hybrids when someone buys the cheapest tires. Hybrids make it real obvious.)

Low tire pressure.

Poor driving habits. Everyone drives different.

That's some common stuff. HTH

EdW2007Civic

I have owned the car for over 4 years, my driving habits have not changed, I buy gasoline year round at the same typical stations, I have replaced tires as needed with OEM tires, chnage the oil regularly.
Always on the highway got 38+ mpg around town never under 35.

In last month or so highway mileage dropped to 33 and lower around town.

So what could have changed????

I've always bragged about the great mpg my none hybrid 5 speed civic provides.

ezone

No idea, not a typical complaint for me to see.
Check engine light on?
Brakes dragging?

Did anything happen 2 months ago that you aren't telling? Was ANYONE under the hood for ANY reason? (JizzyLube screwed up the air filter install?)

Biscuit

Could it simply be that your local gas stations have all switched to the terrible 10% ethanol gas that will reduce MPG by 10%?
I know that when all of the gas stations here got the 10% ethanol gas my (overly maintained) 1989 Integra went from 37mpg to 33mpg burning the ethanol crap-gas. I verified that by going to the only gas station that sold zero ethanol gas several times.

ominousnimbus

Update to OP:

Went to independent mechanic today for an oil change and told them of my troubles. After checking some of the basics, he ended up pulling one of the plugs and claimed that the gap was set to 0.036" (spec is 0.044") on my OEM NGKs, so he "gapped" all four to spec and sent me on my way. I was under the impression that these fancy Platinum plugs were not *supposed* to be gapped, and were always pre-gapped in the box. Rather skeptical this will get me any results (or that they were gapped that poorly in the first place, though I never checked myself) -- the semi-rough idle and hard acceleration didn't seem to be gone on the drive home, but it will take a good highway trip to tell for sure. If not, I suppose I'll give in and try the fuel system cleaning next.

BTW, in response to one of eZone's questions: I drive long distances somewhat regularly this time of year (storm chasing), so going through multiple tanks of gas in one day is routine. In fact, on a long trek this past weekend, I just confirmed for the 3rd of 4th time that mileage and performance drops off over the course of a long drive: recorded MPG of 35.4, 32.8, and 30.2, respectively, on three fillups during an 800-mile haul.

ezone

If it still doesn't run correctly, your gas mileage is not coming back up.

I can't think of anything easy that would take 5-800 miles to get worse, then be fine the next day.

Do you have a mechanic that you trust, one that can SOLVE PROBLEMS?
I think you need to find one.
Not all of us can solve problems.
Maybe about 25% can.
The rest fake it and replace parts until either the problem goes away, or YOU go away.


Yeah, the plugs are pre-gapped at 1.1mm (that is what the 11 is in the plug number!), but that doesn't mean someone didn't drop them on the concrete floor before you got them.
I doubt it.
And they would never close up the gap as the engine runs.




Storm chaser? Cool. I'd think you would want to drive a freekin tank, not a small light car like a Civic.

scooty

Somehow I doubt a simple plug change would cause your MPG to drop like that. I replaced my worn out factory plugs with cheap Autolite plugs that I had to pre-gap my self. Made no difference to the MPG that I could tell. I finally replaced the autolites with the proper NGKs and noticed a slightly smoother idle but the MPG is the same as its always been.

Something else must have happened to your car. Are any of the brakes dragging? Jack up each wheel and make sure they all spin freely.

Is your exhaust manifold cracked? can you hear ticking sounds under load? Could be sucking in air and making the PCM dump fuel into the motor to compensate.

Take off both accessory belts and make sure the alternator, power steering and AC pulleys all turn freely. These could be dragging the motor down.

One of the 02 sensors could be going out, although this should throw a CEL.

The only other thing I can think of is the waterpump might be about to take a dump and is dragging the engine. Has it been replaced? I've seem waterpumps with seized bearings. Usually the timing belt breaks when that happens.

scooty

Somehow I doubt a simple plug change would cause your MPG to drop like that. I replaced my worn out factory plugs with cheap Autolite plugs that I had to pre-gap my self. Made no difference to the MPG that I could tell. I finally replaced the autolites with the proper NGKs and noticed a slightly smoother idle but the MPG is the same as its always been.

Something else must have happened to your car. Are any of the brakes dragging? Jack up each wheel and make sure they all spin freely.

Is your exhaust manifold cracked? can you hear ticking sounds under load? Could be sucking in air and making the PCM dump fuel into the motor to compensate.

Take off both accessory belts and make sure the alternator, power steering and AC pulleys all turn freely. These could be dragging the motor down.

One of the 02 sensors could be going out, although this should throw a CEL.

The only other thing I can think of is the waterpump might be about to take a dump and is dragging the engine. Has it been replaced? I've seem water pumps with seized bearings. Usually the timing belt breaks when that happens.

Biscuit

I can't believe I'm the first to mention this about the plugs in the pic.
The three plugs on the right have failed! Note the blow-by discoloration on the ceramic.
Don't forget to check tire pressure and take into consideration if you recently got new tires.

ominousnimbus

eZone, I don't necessarily have a mechanic I know for certain is "competent at diagnosing problems." I could be so lucky. The one I took it to this week was at the very least more honest and customer-friendly than the stealership I'd been visiting, as the guy ended up pulling and gapping the plugs free of charge, even after I declined the fuel system clean he was trying to push.

Even though it's a bit overwhelming, I'm glad to see a few new ideas on possible culprits. The exhaust manifold crack, in particular, sounded promising. I looked and couldn't see any visually, though.

A brief recap of my exact symptoms:

- Rough idle at startup. If the car has been sitting overnight, it will idle at 1200 rpm (with a bit of mild up and down revving) when it first starts. After driving a few miles and parking, idle is down to 500 rpm.

- Highway fuel economy that's marginally worse right out of the driveway (~34-35 mpg), dropping off to significantly worse (~30-32) over the course of several hours driving at high speed.

- Decreased performance at high speed, getting worse over several hours of high-speed driving. Seems like higher rpm is required to go the same speed and accelerate once above 50-60 mph or so, vs. before the issue appeared.

- NO CHECK ENGINE LIGHT, ever, that I've noticed. Scanner showed no codes.

Issues already covered:
- Definitely not just fuel mixture/ethanol, headwind, or anything that simple.
- Definitely not tire pressure (all tires set 2 psi above spec).
- Don't think brakes are dragging (wouldn't explain rough idle anyway).

Question: would it be worth asking the mechanic to do cylinder compression tests? If the manifold is cracked, would that indicate it? More generally, if I take it back in, what tests should I ask for? At this point, I'm not even trying to diagnose myself... it's just that I can't find a mechanic willing to tackle the problem on their own, so I'm going to need to ask for specific checks/tasks.

ezone

"if I take it back in, what tests should I ask for?"
I really hate when someone comes in with this attitude, because this is MY job. Drivability problems are my area of expertise. I decide what tests I do, not the customer.
You don't go in to a doctor telling him to do this test or that test, do you? You say "Doc, this hurts" and he starts asking questions. Every answer gets a different next question.

I just decided you have been on some damn forum, you dont trust anyone under the hood of your car, and you must think all I can do is drag my knuckles across the shop floor while swinging a monkey wrench.
*rolls eyes*
I know what you are trying to deal with though. I can't help that.







I would have had a scanner on it long ago, but you probably don't have that option and wouldn't make heads or tails of the data if you did have it.

It is real tough for me to say what to test, I don't really have a set of standard tests to run for every problem car.
I don't bother doing tests that I don't feel that it will give me needed results and data. I only run tests that I feel will give valuable results and data and direct answers.
Every drivability problem is different, and each situation requires its own evaluation and approach. It isn't always systematic, that wastes valuable time for me. My mind probably operates far differently during diagnosis than any books can/will tell you.

I start with the symptoms that the customer notices.
Then test drive, hopefully under the conditions that the customer described so I can feel the problem. Maybe I can tell other important things that the driver didn't notice.
Seat-of-the-pants-feel (the Butt Dyno) tells me more than you could ever know. You can't video a feeling.
Then figure out what my next step is.

If I can diagnose it from the comfort of the drivers seat, I sure as hell am going to do it that way.


Randoms:
Cam timing.
Backpressure. Has the exhaust been mashed anywhere?
Scan data can tell me an awful lot about what the computer is doing. This takes a great scanner and lots of experience.
Fuel pressure. Fuel delivery.
Also set up the fuel pressure gauge to monitor as you drive, see what it does over the course of your 800 mile day.
Same with scan data. Same with most anything I can think of. I'd want to monitor everything while driving, if nothing stood out as blatantly wrong at the start.
Accuracy of temp senders. Fuel trims. O2 sensor readings. Much much more that is only found in a datalist.
Could be something as simple as poor grounds, but that is really hard to tell sometimes.
Complicated problems have simple solutions sometimes.
Some people are seeing PCM problems with similar symptoms, although I haven't seen that here yet. (May be a geographical phenomenon.)

What RPM is it doing at 60 MPH, since you say it is now higher than it used to be?
Ever had a timing belt? (it is due now if it hasn't been done.)
Are the alternator bolts tight?

You said "Definitely not just fuel mixture" up there, but you really don't have any way of knowing that. A scanner and/or a gas analyzer is about the only ways to evaluate this.

Exhaust manifold leakage, I would think that if you (or anyone else) were observant you would hear and smell exhaust leaks from the manifold area. Yes, it could drop gas mileage a wee bit if it had leakage, but IDK how much. Fresh air can fool the O2 sensor into making the PCM feed extra fuel. But again, you should be able to hear exhaust leaks that would make a difference this big.

Where are you located? (City, State) Maybe I can hook you up with a shop.

ezone

Oh yeah, I finally realized what your handle is, and that it goes with the storm chasing.
I'm slow.

Gotta go, the short bus is honking!