Loss of MPG, performance after spark plug change
05-09-2012
#32
If you think a good mechanic is expensive, try hiring a bad one
05-09-2012
#33
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Re: Loss of MPG, performance after spark plug change
"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.
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.
I completely understand your gripes and your perspective. The fact is, though, both of the places I've taken it were disinterested in actually diagnosing the problem. I'm not surprised at this, since a) just trying things like a fuel system cleaning first makes them free money (after which they can actually diagnose if necessary), and b) the conditions under which my problems appear (at least perceptibly) require taking the vehicle out on the interstate for long periods and/or leaving it overnight to get a cold start.
In fact, the only practical way they'd be able to get scanner data while the poor high-speed MPG/performance is occurring would be for them to loan me one for a few days when the next storm system rolls in...
Timing belt and water pump were replaced just two months ago at 110k, BTW, after the issue was already occurring. RPM does not *seem* different at low-moderate speeds around town, though accelerating might be a little tougher. This is all just my best guess, though, and while I'm not a car guy, I completely understand the need for quantitative data. Would love nothing more than to have someone capable gathering and interpreting it...
05-09-2012
#34
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Re: Loss of MPG, performance after spark plug change
I don't think so. That's exactly what my autolites looked like when I pulled them out and I didn't have any problems. The plugs in my Firebird also get that discoloration. It's just oxidation at the ceramic/metal interface. Those plugs are fine.
05-09-2012
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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).
- 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).
Secondly, it is simply not possible for your rpms to be higher than they were before at the same highway speed. If that is indeed happening, your transmission is slipping really bad or the torque converter is not locking up and you have way bigger problems. Check the tranny fluid just in case. It should not be low and should not smell burnt.
Third, what makes you think the brakes are not dragging? All it takes is a bad caliper at just one of the wheels. You could have bad wheel bearings too. If you don't want to jack up the wheels at least see if you notice the car slowing down faster then it used to while coasting. Then touch each rim after a drive to see if they're all the same temp. Dragging brakes heat up rims very quick.
Try a different brand of gas. Something could have happened with the gas at your usual station.
05-09-2012
#36
If you think a good mechanic is expensive, try hiring a bad one
Re: Loss of MPG, performance after spark plug change
^^Sort of agree, the idle thing is pretty subjective at this point, since none of us can actually witness it to tell if it is average or not.
--------------------------------------------
On the trans description thing, the feeling I get is that he has to use far more throttle than he should be, to keep up a certain speed. Lacking engine power, instead of a trans problem.
Of course, it could be any of 200 things that could cause a lack of power.
I wonder if this is readily apparent while driving, like in the first 5 or 10 miles or less. I understand it may gradually get worse over 800 miles, but it is obvious there is something wrong right off the bat? If it is, then that is a solid and repeatable condition that can be chased. Figure that part out and you should be well on your way to finding the key to the whole puzzle.
----------------------------------------
Yes, feel wheel temps after a drive. Fronts are normally quite a bit hotter than the rears, because fronts do 80% of the work.
However, I doubt this is the issue.
--------------------------------------------
On the trans description thing, the feeling I get is that he has to use far more throttle than he should be, to keep up a certain speed. Lacking engine power, instead of a trans problem.
Of course, it could be any of 200 things that could cause a lack of power.
I wonder if this is readily apparent while driving, like in the first 5 or 10 miles or less. I understand it may gradually get worse over 800 miles, but it is obvious there is something wrong right off the bat? If it is, then that is a solid and repeatable condition that can be chased. Figure that part out and you should be well on your way to finding the key to the whole puzzle.
----------------------------------------
Yes, feel wheel temps after a drive. Fronts are normally quite a bit hotter than the rears, because fronts do 80% of the work.
However, I doubt this is the issue.
05-10-2012
#37
If you think a good mechanic is expensive, try hiring a bad one
Re: Loss of MPG, performance after spark plug change
Location is Norman, OK, USA.
I'm looking, give me time here. I'll fire a PM at you if I get something.
I completely understand your gripes and your perspective. The fact is, though, both of the places I've taken it were disinterested in actually diagnosing the problem.
There isn't any good profit in proper repairs. This is a business model. The guys that generate a sh1tton of revenue are the people that fire the parts cannon. They look great to bean counters, the numbers look great on a spreadsheet.
Handy pic of a parts cannon:
On that same note, here is a Parts Airdrop:
a) just trying things like a fuel system cleaning first
Won't fix it.
makes them free money
It's called "Gravy".
(after which they can actually diagnose if necessary),
You mean "if possible": car or mechanic.
and b) the conditions under which my problems appear (at least perceptibly) require taking the vehicle out on the interstate for long periods and/or leaving it overnight to get a cold start.
You may have been put into the category of "crack smoker".
In fact, the only practical way they'd be able to get scanner data while the poor high-speed MPG/performance is occurring would be for them to loan me one for a few days when the next storm system rolls in...
Need a Flight Recorder.
though accelerating might be a little tougher.
This should be easily verified, and if true, be an easy thing to chase (diag).
I'm looking, give me time here. I'll fire a PM at you if I get something.
I completely understand your gripes and your perspective. The fact is, though, both of the places I've taken it were disinterested in actually diagnosing the problem.
There isn't any good profit in proper repairs. This is a business model. The guys that generate a sh1tton of revenue are the people that fire the parts cannon. They look great to bean counters, the numbers look great on a spreadsheet.
Handy pic of a parts cannon:
On that same note, here is a Parts Airdrop:
a) just trying things like a fuel system cleaning first
Won't fix it.
makes them free money
It's called "Gravy".
(after which they can actually diagnose if necessary),
You mean "if possible": car or mechanic.
and b) the conditions under which my problems appear (at least perceptibly) require taking the vehicle out on the interstate for long periods and/or leaving it overnight to get a cold start.
You may have been put into the category of "crack smoker".
In fact, the only practical way they'd be able to get scanner data while the poor high-speed MPG/performance is occurring would be for them to loan me one for a few days when the next storm system rolls in...
Need a Flight Recorder.
though accelerating might be a little tougher.
This should be easily verified, and if true, be an easy thing to chase (diag).
05-29-2014
#38
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This seems to be an old thread but I still thought it would be a worthy effort to post my recent experience (of loss in mpg after I changed my spark plugs) since it drove me crazy. It caused around 15-20% degradation (from ~28 MPG it fell to around 23 MPG) and caused a lot of heartburn every time I filled up my tank.
So, I have a Honda Civic 2004 and I took it for a 60K service about 6 months back (yeah, I know you are thinking...low miles).
Even though spark plugs are meant to be changed at 100K, the bozo irecommended that I should change it since the original spark plugs could seize up on me at anytime. I agreed.
He installed the NGK PZFR6F-11 Laser Platinum Spark Plug which is the recommended OEM.
Right from day one, I could see that the idle was no longer as smooth as it was before the spark plug change. After a couple of tanks of driving, when I reported a loss of MPG, the bozo claimed that spark plugs take sometime to "break in" and the original MPG should be restored after sometime.
After ~1K miles, I lost my patience and went back to the shop. He swapped the spark plugs again with a brand new set of the same type (NGK PZFR6F-11 Laser Platinum Spark Plug). The issue still persisted.
So, I go to another mechanic. He mentioned that Hondas are sensitive to spark plugs and that we should go for Iridium ones. He recommended Bosch Iridium spark plugs.
I was wary of putting anything other than Denso or NGK into my Honda Civic but he assured me that Bosch were good. I reluctantly agreed.
But whoa!! Knock of the wood!! My MPG has been restored to around 27-28 MPG (city) and > 37 (highway) as it was before, and my car is much smoother than it was with NGK.
So, there are two possibilities:
1. Hondas indeed like Iridiums over Platinums...Indeed, when I asked a Honda dealer what do they use for replacement, they mentioned NGK Iridiums (and not NGK platinums as per Honda official website).
2. The NGK Platinums that were installed in my car were counterfeits....
I just dunno what it was but I am happy to get my MPG back....
Hope my post benefits someone who underwent similar pain and heartache....It is not fun to be paying 20% more in SoCal where gas prices are one of the highest...
So, I have a Honda Civic 2004 and I took it for a 60K service about 6 months back (yeah, I know you are thinking...low miles).
Even though spark plugs are meant to be changed at 100K, the bozo irecommended that I should change it since the original spark plugs could seize up on me at anytime. I agreed.
He installed the NGK PZFR6F-11 Laser Platinum Spark Plug which is the recommended OEM.
Right from day one, I could see that the idle was no longer as smooth as it was before the spark plug change. After a couple of tanks of driving, when I reported a loss of MPG, the bozo claimed that spark plugs take sometime to "break in" and the original MPG should be restored after sometime.
After ~1K miles, I lost my patience and went back to the shop. He swapped the spark plugs again with a brand new set of the same type (NGK PZFR6F-11 Laser Platinum Spark Plug). The issue still persisted.
So, I go to another mechanic. He mentioned that Hondas are sensitive to spark plugs and that we should go for Iridium ones. He recommended Bosch Iridium spark plugs.
I was wary of putting anything other than Denso or NGK into my Honda Civic but he assured me that Bosch were good. I reluctantly agreed.
But whoa!! Knock of the wood!! My MPG has been restored to around 27-28 MPG (city) and > 37 (highway) as it was before, and my car is much smoother than it was with NGK.
So, there are two possibilities:
1. Hondas indeed like Iridiums over Platinums...Indeed, when I asked a Honda dealer what do they use for replacement, they mentioned NGK Iridiums (and not NGK platinums as per Honda official website).
2. The NGK Platinums that were installed in my car were counterfeits....
I just dunno what it was but I am happy to get my MPG back....
Hope my post benefits someone who underwent similar pain and heartache....It is not fun to be paying 20% more in SoCal where gas prices are one of the highest...
05-29-2014
#39
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^I've had good luck with Bosch plats (+4 FUSION) in my past cars. However, some makes and models hate them, like Chevy trucks, at least the old 4.3L & 5.3L Vortecs. My '99 Escort loved them, and my Toyota Paseo actually had great off-idle flexibility with them (far more than the stock copper NGKs).
Solved a similar idle wonkiness problem with NGK plugs on my '04 EX, with the Denso OEM ones (PKJ20CR-M11), which are painfully expensive, but they fixed *all* of the driveability problems and won't need replacement until long after the car is in salvage.
Solved a similar idle wonkiness problem with NGK plugs on my '04 EX, with the Denso OEM ones (PKJ20CR-M11), which are painfully expensive, but they fixed *all* of the driveability problems and won't need replacement until long after the car is in salvage.
Last edited by kinakoes2; 05-29-2014 at 01:53 AM. Reason: Clarif
05-29-2014
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Yes, I think NGK Platinums should no longer be the recommended plugs. I know another couple of folks who went through this.
Last edited by gkpar; 05-29-2014 at 03:18 PM. Reason: Misread the earlier post
06-13-2014
#41
Re: Loss of MPG, performance after spark plug change
Sorry to bump this old thread. But, I have had a similar loss in MPG on my 2001 LX Civic over the past few years. I changed my spark plugs to the NGK's as well, and, I can't recall if that's what did it, but I know that ever since then, my average highway MPG's has dropped from 42-44 mpg to around 38 mpg.
06-14-2014
#42
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After my exp with the OEM NGKs and the dramatic difference in driveability with the recommended Densos... the Densos are the only one I feel comfortable endorsing. Not really sure why this engine is so sensitive to not having one (1) brand and spec of spark plug in it, despite the difference in tune between the EX and DX/LX...
BTW... there's no way I could get even your NGK mileage with my EX. I get, at best... 36 mpg (EX has sportier -- read shorter -- gearing than the manual, non-VTEC 7th-gens). :/
06-14-2014
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Sorry to bump this old thread. But, I have had a similar loss in MPG on my 2001 LX Civic over the past few years. I changed my spark plugs to the NGK's as well, and, I can't recall if that's what did it, but I know that ever since then, my average highway MPG's has dropped from 42-44 mpg to around 38 mpg.
06-15-2014
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The CRZ wasn't built to get mpg numbers, despite being a hybrid (34 combined, you kidding me? That's the same as my short-geared, 4-dr-heavy EX sedan with my leaden foot, thicker oil and 80 lbs of crap in the back seat and trunk). 
Blame unacceptable curb weight, along with ill-conceived, non-competitive IMA hybrid tech (which Honda got halfway right on the newest Accord Hybrid, finally. Still doesn't even get close to EPA numbers, though).
Blame unacceptable curb weight, along with ill-conceived, non-competitive IMA hybrid tech (which Honda got halfway right on the newest Accord Hybrid, finally. Still doesn't even get close to EPA numbers, though).
06-15-2014
#45
If you think a good mechanic is expensive, try hiring a bad one
Re: Loss of MPG, performance after spark plug change
The CRZ wasn't built to get mpg numbers, despite being a hybrid (34 combined, you kidding me?
I heard some time ago that Honda wanted to quit focusing on being an engineering company and in turn, focus on being a marketing company......
Yeah, that ought to work well....
I think Hondas marketing department missed by a mile on the CRZ......and a few other cars as well.
You know there's a supercharger kit that's supposed to be available for the CRZ....... (Nobody has let me install one yet.)
Along with red calipers, slotted rotors, Limited Slip differential, 6 puck clutch.
http://automobiles.honda.com/cr-z/hpd.aspx
06-24-2014
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4-6 mpg down is a large difference. Did you do the idle learn after swapping?
After my exp with the OEM NGKs and the dramatic difference in driveability with the recommended Densos... the Densos are the only one I feel comfortable endorsing. Not really sure why this engine is so sensitive to not having one (1) brand and spec of spark plug in it, despite the difference in tune between the EX and DX/LX... :/
After my exp with the OEM NGKs and the dramatic difference in driveability with the recommended Densos... the Densos are the only one I feel comfortable endorsing. Not really sure why this engine is so sensitive to not having one (1) brand and spec of spark plug in it, despite the difference in tune between the EX and DX/LX... :/
Not sure the difference between L11 v. M11 but the engine runs MUCH smoother. The previous owner had Bosch platinum plugs, the kind with the two electrodes.
Is the idle learn procedure in the DIY section? (I'll search for it)
06-24-2014
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^
Hey smiley -- idle learn is super-easy. Just turn off ALL electrical loads (lights, fan, radio, A/C) and let it idle until op temp.
Then, let it idle for five full mins NOT COUNTING WHEN THE COOLING FAN COMES ON. Use a timer, and watch the fan, hood up. When it comes on, stop the timer. When it goes off, resume the timer.
The L11 and M11 are different in that one (M11) has a larger ground electrode, which matters only in how long its service life is. PKJ means a plat plug, so it'll fire similarly enough, just not last 100K, is my guess. The proof is in how it behaves, so well done! Just may last 60K rather than 100K.
If there are any running issues afterwards, let us know.
Hey smiley -- idle learn is super-easy. Just turn off ALL electrical loads (lights, fan, radio, A/C) and let it idle until op temp.
Then, let it idle for five full mins NOT COUNTING WHEN THE COOLING FAN COMES ON. Use a timer, and watch the fan, hood up. When it comes on, stop the timer. When it goes off, resume the timer.
The L11 and M11 are different in that one (M11) has a larger ground electrode, which matters only in how long its service life is. PKJ means a plat plug, so it'll fire similarly enough, just not last 100K, is my guess. The proof is in how it behaves, so well done! Just may last 60K rather than 100K.
If there are any running issues afterwards, let us know.
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