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I am stumped guys?! A few months ago I did some maintenance. All 4 rotors and brake pads, new Continental DWS06 tires, side engine mount, spark plugs and flushed the power steering fluid. During the power steering fluid flush the hose came off and fluid went everywhere on that side of the engine, I washed off all the fluid I could. Since that day my gas mileage went down, not a lot, but about 2 miles per gallon consistently. I now get about 17-18 city and just got back from a 10 hour trip and it was 25-28 (different conditions). I know those figures are within the range of the TL but I used to get better than that. There was a change from before to after the maintenance.
Some things I have checked: Rotors and pads to see if they were dragging, they are not. Made sure spark plug gap was correct. Have had many tanks of gas since then, no change. Car runs fine, at times it seems a little sluggish but I know it can when its warm out. I really have no idea and it bugs me because I know something isnt right and I dont want to throw parts at it that do not do anything. I know its a long shot but I figured I would ask because maybe I am missing something. Thanks as always guys!
Tires, tires, tires....can easily account for a 2MPG change. I know my switch from the OE EL42 to PilotSport AS+ dropped my MPG by 2-3MPG (it may have been more...it has been several years). It recovered a bit when I went to MXM4, but still not quite as high as the EL42 were.
Have your valves been adjusted? Generally the recommendation is with the 105k maintenance. As far as I know, the valves being out of spec will cause noise and potentially decrease fuel economy. I have 111k on my car and haven't done the valves, but I get 30-31 MPG on the highway doing 70+. I did a 10 hour round trip last weekend and averaged 30 MPG across about 650 miles.
Another causes of poor fuel economy that I can think of would be a failing O2 sensor. However, when I had a CEL for a bad sensor, I was still getting 30 MPG.
New tires can have a different rolling resistance coefficient resulting in less or more MPG. What brand and model were your previous tires?
I had Continental Tires before, I think they were Continental Control Contact (?).
Why did you change the plugs? Are they NGK 6994?
I am getting near the 105K service and wanted to do the plugs myself. Yes they are NGK 6994.
Tires, tires, tires....can easily account for a 2MPG change.
There was some time between the tires and other items, so I noticed the change in MPG's before the tires were done.
I only ever use premium fuel, valves have not been adjusted as I'm not at the 105k milegage yet, also I dont have any noise.
I was wondering about the O2 sensor and thought about changing it, I thought maybe some power steering fluid got on the wiring. I guess I could just spend the $100 and see, but didnt want to throw money at it. No check engine light.
Last edited by eastcoastguy; 06-06-2017 at 11:32 AM.
Tires, tires, tires....can easily account for a 2MPG change. I know my switch from the OE EL42 to PilotSport AS+ dropped my MPG by 2-3MPG (it may have been more...it has been several years). It recovered a bit when I went to MXM4, but still not quite as high as the EL42 were.
I saw the same when I replaced the EL42s as well. I've also seen the same thing on other cars when replacing OE tires. The OEMs absolutely pick tires to get the ratings up. I know there were a lot of EL42 haters but 2 MPG tank-over-tank isn't statistically insignificant. But realistically I think it's like an extra $85 year (10,000 mi, 2.70/gal, 26 down to 24 MPG). Not enough to really make it worth passing up better tires.
I saw the same when I replaced the EL42s as well. I've also seen the same thing on other cars when replacing OE tires. The OEMs absolutely pick tires to get the ratings up. I know there were a lot of EL42 haters but 2 MPG tank-over-tank isn't statistically insignificant. But realistically I think it's like an extra $85 year (10,000 mi, 2.70/gal, 26 down to 24 MPG). Not enough to really make it worth passing up better tires.
Keep in mind new tires typically reduce fuel economy; nature of the beast. Over the years I've only replaced like for like in tires twice, and both times the new tires reduced the fuel economy, and then gradually it crept back up as the tires wore.
2 MPG is a significant decline in mileage @ 10% in city driving, so I'd look at something that has change in engine operation
e.g. O2 sensor operation, EGR system, vacuum leak, check air intake system/tube for cracks/leaks.
I went back through my old posts and found my comments that my tire switch dropped my MPG by 3-5 on the highway. However seeing your point that the tires were not done exactly at the same time you initially noticed the drop....I don't know. In my experience, tires, fuel quality/type, and most importantly....driving habits have impacted my MPG the most. How I drive and where I drive tend to impact my MPG the most.
I went back through my old posts and found my comments that my tire switch dropped my MPG by 3-5 on the highway. However seeing your point that the tires were not done exactly at the same time you initially noticed the drop....I don't know. In my experience, tires, fuel quality/type, and most importantly....driving habits have impacted my MPG the most. How I drive and where I drive tend to impact my MPG the most.
Yea I dont know either and its very frustrating, esepcailly since I enjoy working on the car and saving money is nice but then I wind up creating other problems. Yea I can rule out the tires, rule out fuel since its been a few months and my drive tends to be the same week after week for the most part. I have driven hard and very light and the difference was still there. I may just replace the oxygen sensor and see if that does anything. I think when I am in for my next oil change I may have them check the brakes despite me checking them to make sure I didnt miss something and maybe they are dragging slightly. Other then that I have no idea.
Well, did a couple things to see if I could figure this thing out. Got the A/C done because it was low on freon causing it to freeze up on long drives, probably will have no effect but it needed to be done.
Also, took off rear calipers and brackets and checked pins, etc. and adjusted parking brake, it was rubbing slightly, cross that off the list.
I also took all three front coil packs off and and unplugged them, put them back on making sure they were on good and plugged and unplugged them a couple times to make sure they had a good connection. I dont know if its just my butt dyno, but that seemed to have an affect on how the car feels, doesn't feel as sluggish and responds better. We will see if this impacts gas mileage, will have to go through a couple tanks to see. I am soo hoping that was it.
The brakes may have been the issue; properly plugged in coils, I'm thinking not so much. Why? As a general rule, if one or more coils are not properly plugged in, you'll get a check engine light pretty quickly.
Yea, i doubted the coils but figured I would check them and it was weird that it felt different, guess in my head. Drove the car today and its back to being sluggish at lower RPMS, although it was hotter and more humid today. So i guess the saga continues, sigh!!!
So I went and purchased another set of spark plugs to install to rule out they are the problem. When I purchased them and installed the last time I found out the gap was wrong, so i regapped and installed but no change so I thought maybe they had been damaged. Well another set of plugs from a different place and the gap from the factory is incorrect again. Not .044 but .037. I know gap is important to gas mileage and performance so I am struggling to figure out why they are gapped wrong. I have the right plugs. I may return the new ones because the incorrect gap I thought could be damaged original ones is just how they come it seems.
Last edited by eastcoastguy; 07-20-2017 at 01:13 PM.
"Thank you for your E-mail. The Laser Iridium IZFR6K11 is produced on the assembly line at a 1.1mm gap ( this is where they get the 11 in the part number from). You cannot check gap with a coin style gapping tool due to the fine wire design, a wire or feeler gauge is required. These is a OE replacement design, meaning this is the same spark plug used when the vehicles engine was produced. They do not adjust gap at the factory. Recommended gap is a range, not a specific number. If you want to adjust gap you can, just use a tool that does not put any force on the fine wire center electrode."
I swear this car makes me think I am crazy. Did the new spark plugs yesterday (I'm getting good at changing them) all gapped and torqued correctly.) Took it out for a drive and its responsive but seems to have to work a little harder now and there seems to be more vibration on accelerating. The other plugs were gapped at .047 and the new ones at .043. Today I did a couple heavy accelerations and got a rotten egg smell and I dont remember getting that before. I have yet to see if the gas mileage will change. Are these cars that sensitive to gap? And I think I am crazy for either noticing these changes or its all in my head. I think since I know the plugs are right and within spec that I am going to not worry about it (maybe I am too anal), if the gas mileage doesnt change I am over that too because I dont know whats causing it.
I am stumped guys?! A few months ago I did some maintenance. All 4 rotors and brake pads, new Continental DWS06 tires, side engine mount, spark plugs and flushed the power steering fluid. During the power steering fluid flush the hose came off and fluid went everywhere on that side of the engine, I washed off all the fluid I could. Since that day my gas mileage went down, not a lot, but about 2 miles per gallon consistently. I now get about 17-18 city and just got back from a 10 hour trip and it was 25-28 (different conditions). I know those figures are within the range of the TL but I used to get better than that. There was a change from before to after the maintenance.
Some things I have checked: Rotors and pads to see if they were dragging, they are not. Made sure spark plug gap was correct. Have had many tanks of gas since then, no change. Car runs fine, at times it seems a little sluggish but I know it can when its warm out. I really have no idea and it bugs me because I know something isnt right and I dont want to throw parts at it that do not do anything. I know its a long shot but I figured I would ask because maybe I am missing something. Thanks as always guys!
Just curious, when you did your spark plugs, did you change out the existing ignition coils for each plug? They aren't cheap. My trusted local mechanic suggested doing so if you're already putting in new spark plugs...but thought I'd ask people what they did.
Just curious, when you did your spark plugs, did you change out the existing ignition coils for each plug? They aren't cheap. My trusted local mechanic suggested doing so if you're already putting in new spark plugs...but thought I'd ask people what they did.
I cannot come up with a single engineering reason why one would want to replace the coils at every spark plug change. The thing is, some coils will go 300,000 or more miles while others will fail after only 50,000 miles. If one was to replace the coils at every spark plug change, they might well be throwing away a coil which would otherwise be good for an additional several hundred thousand miles with one which will fail in the next few years.
Long story short, replace coils as they fail and not before.
I havent replaced the coils and see no reason to. I agree with the others that there really is no reason unless something is wrong. My issue doesnt seem to be coil related so those are off the list.
Thanks to everyone for sharing your inputs. I don't think I mentioned that my car is at 144K miles and has original spark plugs and ignition coils. The subjective inputs from people across various posts (in this forum and others) lean towards "replace when needed". But there's a chorus of people with cars pushing 150K+ that one should go ahead and change them. Then there's a smaller group who change them at every spark plug change at 50K (approx.) intervals. I don't think that would be me though.
Again, appreciate everyone's inputs. I'm going to keep thinking about it. The military guy in me is trained to not wait until equipment fails to react...but rather to follow a preventive maintenance approach so that there's a higher likelihood of equipment functionality/reliability. That's where spending money to me, is a good investment. I am also weighing in my mechanic's advice to replace them at this time esp. since they are the 1 Honda only shop where more often than not they tell me to not worry about changing something to save money and I've walked out of there not spending anything...so if they are advising me to do so, I have to weigh that in.
Case in point regarding the coils on Honda J-Series engines; my Honda Accord with the J30 engine has just over 190,000 miles on the clock, five of the six coils are from the factory, the sixth failed at about the 170,000 mile mark. I'll lay odds by the time the car hits 300,000 miles, no more than two additional coils will fail (one of which might could well be the replacement coil).
I'm former military as well (USMC), the thing is, if an individual component is going to fail in such a way as to strand me, I might actually give some thought to a prophylactic replacement. When it comes to ignition coils, not a chance. Why? When they fail the CEL is illuminated and the engine runs a bit rough, but otherwise the car is still drivable.
Case in point regarding the coils on Honda J-Series engines; my Honda Accord with the J30 engine has just over 190,000 miles on the clock, five of the six coils are from the factory, the sixth failed at about the 170,000 mile mark. I'll lay odds by the time the car hits 300,000 miles, no more than two additional coils will fail (one of which might could well be the replacement coil).
I'm former military as well (USMC), the thing is, if an individual component is going to fail in such a way as to strand me, I might actually give some thought to a prophylactic replacement. When it comes to ignition coils, not a chance. Why? When they fail the CEL is illuminated and the engine runs a bit rough, but otherwise the car is still drivable.
Good info thanks. Never experienced a CEL other than when the APP Sensor went bad and I replaced it myself...so no experience with any cars to date with spark plug or ignition coil failures (nor have I read about what other people experience in that case...so I'll have to research if my car will behave the same way). I do remember that with the APP sensor, the car was drivable but it was on a road trip out of state. I'll lay odds that if I get a situation with degraded performance it'll happen when I'm on a road trip. LOL. Semper Fi.
I saw the same when I replaced the EL42s as well. I've also seen the same thing on other cars when replacing OE tires. The OEMs absolutely pick tires to get the ratings up. I know there were a lot of EL42 haters but 2 MPG tank-over-tank isn't statistically insignificant. But realistically I think it's like an extra $85 year (10,000 mi, 2.70/gal, 26 down to 24 MPG). Not enough to really make it worth passing up better tires.
Just a shout out to Adobeman for your posts on DVD audio authoriing. I've created many DVD-As for my TL b/c of your knowledge sharing posts. Kudos and hats off to you. (sorry, I know it's off topic for this post but I'll risk it in the spirit of giving someone props)
06-06-2017, 12:29 AM
Preventative maintenance = lower MPG's
Yea I can rule out the tires, rule out fuel since its been a few months and my drive tends to be the same week after week for the most part. I have driven hard and very light and the difference was still there. I may just replace the oxygen sensor and see if that does anything. I think when I am in for my next oil change I may have them check the brakes despite me checking them to make sure I didnt miss something and maybe they are dragging slightly. Other then that I have no idea.
