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2006 Prius huge MPG drop. Why??

Discussion in 'Gen II Prius Fuel Economy' started by 06_PriusDriver, Feb 27, 2012.

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  1. 06_PriusDriver

    06_PriusDriver Junior Member

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    Hello all

    I have been reading over quite a few of the posts in this section to try and get some ideas as to why my Prius's MPG has dropped. Right now I am seeing roughly 41 MPG and that is after changing the spark plugs with brand new NGK Iridium's, Air intake filter and did an oil change since it was due for one.
    I have driven the car roughly 2,500 miles since all of this stuff was done and it just seemed to continue to drop to the 41 MPG mark.

    What I have noticed though is that when the motor turns off it shudders and the when it restarts while the car is in park the car will roll back and forth slightly. I have also noticed that the car seems to struggle to get up to the posted speed while climbing an incline and also while the car idles in park or at a complete stop there seems to be a bit of a miss fire. Could that be caused by a bad coil? Because I have tried everything short of taking it to the dealer which I really do not want to do again and be told there is nothing wrong with it when I know there is.

    Any help with this issue would be greatly appreciated. Thank you in advance!
  2. tv4fish

    tv4fish Member

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    Sounds like you're thinking the ICE IS the problem for sure?? Just a couple of ???'s - Have you changed the transaxle fluid ? Have you done a compression check?
    IMO - Your "cold weather" mileage is not that far off! In the Summer, we get 50-52 mpg. In the cold Winter - it does drop to 44-48.
  3. 06_PriusDriver

    06_PriusDriver Junior Member

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    Well the last time I had it in to Toyota for service just before the fall they apparently checked the trans axle fluid and checked for valve clearance and said everything was fine even though this car was seeing about 46 MPG at that point in time with out running the air conditioner.
  4. bisco

    bisco cookie crumbler

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    you went from 46 to 41, i went from 65 to57. sounds about right for winter. what did you get last winter?
  5. SageBrush

    SageBrush Senior Member

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    If I thought it possible, I'd say you changed the order of cylinder firing. How about bad plug, mis-seated plug, or poorly attached plug ?
  6. 06_PriusDriver

    06_PriusDriver Junior Member

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    Apparently according to my wife the fuel consumption was a lot worse than this year. She said it was down around the 30 MPG mark.. OUCH! So I guess the change in the plugs and the air filter did make some difference from last year. Yet I have seen others on here that are still getting at least 50 MPG during the winter and I sure am not seeing that. Before I changed the plugs I was seeing 46 MPG (5.1 Liters/100 kms) and that was during the summer. Either there is an underlying problem or otherwise we are doing something wrong lol. Really the thing that strikes me as bizarre is my old 95 Corolla got way better MPG than this Prius:eek:.
  7. 06_PriusDriver

    06_PriusDriver Junior Member

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    No did not change the firing order which is kind of hard to do since everything is crammed in there lol :D. I had thought of a defective plug but then I thought back to before the plugs were changed and it still had a miss fire. I also pulled the coil boots and the plugs one by one and reinstalled them with no change. I also used a little dielectric grease on each boot just to make sure moisture was not the culprit. The dielectric grease seemed to help tone down the miss fire for about 10-20 miles. So that got me to thinking maybe one of the coils are leaking a little bit but not to the point where the engine will not start when damp.
  8. fotomoto

    fotomoto Senior Member

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    46 to 41 is not a HUGE drop rather it's a common variance going from summer to winter.

    Did you use a different brand of plugs?
  9. V8Cobrakid

    V8Cobrakid Green Handyman

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    in relation to the coils, when they fail, you see around 30mpg.. you also see the ice on all the time (a lot more than normal) and high revs along with reduced power (or at least when it fully fails). my car didn't throw codes, i had to pull the coils up and out 1 by one to figure out which cylinder wasn't firing. if two cylinders fail to fire, it throws a code and turns off the ICE. replace the coil, restart the car (preferably in maintenance mode) and check the next coil. my coil was coil#1

    i'm surprised someone hasn't asked about your 12v. it's due for replacement if you haven't done so.
  10. 06_PriusDriver

    06_PriusDriver Junior Member

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    The only difference was I used NGK plugs instead of the OEM Denso plugs the dealers would install.
  11. cwerdna

    cwerdna Senior Member

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  12. 06_PriusDriver

    06_PriusDriver Junior Member

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    There has been a decrease in power and the engine seems to rev more than it should to climb an incline. My car is not throwing any codes either but please excuse me for my lack of Hybrid knowledge but what is the ice for? The only thing that I see is the ready light on the dash and that is it other than the display for the consumption and etc. However I assume that the 12v is the battery for the electric motor?
  13. wjtracy

    wjtracy Senior Member

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    No in the trunk you have a smaller 12v battery that needs replacing about now if you have not replaced as of yet. You can go with Toyota or Optima is what many here incl me have used. Cost about $150-200. Of course the bigger Hybrid traction battery costs more to repace if that turns out to be the problem.
  14. cwerdna

    cwerdna Senior Member

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    ICE = internal combustion engine

    No, the 12 volt is NOT for the electric motors in the power split device/transaxle. It might be worth skimming thru the hybrid articles on AUTOMOTIVE TECHNICAL ARTICLES.

    Agree w/earlier comments that the 12 volt battery should probably be replaced by now anyway. To find out what kind of state it's in, you can do http://priuschat.com/forums/newbie-forum/73400-weird-stuff-happening-mpgs-dropping-test-battery.html after the car has sat overnight or for many hours. If you have HID lights, you can save wear/tear on them by only flipping between off and the parking light position instead of all the way on.
  15. 06_PriusDriver

    06_PriusDriver Junior Member

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    I was not sure where I was supposed to paste this so please forgive me if I have pasted this in the wrong spot :cool::cool:

    - Have you read This Thead Yet? Yes

    - What fuel economy are you getting and how are you determining fuel economy? (trip computer or manual calculations) 41MPG

    - What fuel economy are you expecting and why? 50 MPG. Because a lot of others are seeing that or better during the winter and the summer.

    - What are the approximate outside air temps? Between -6c to +6c

    - How long are your trips? long trips- 124 miles or more. Short trips 10-62 miles.

    - How much of it is city vs. highway? Roughly what's the average speed in overall and and of each segment? Is there a lot of stop and go driving? Most of the driving has been highway. Rough overall speed 50 MPH-65 MPH

    - What region/state are you in? (if you haven't set your location in your profile) Ontario, Canada

    - What's the terrain like of your drives? (e.g. flat, gentle hills, steep hills, etc.) Mostly flat with some gentle hills.

    - Is your oil overfilled? (i.e. above the full mark on the dipstick) No

    How old is your 12v battery? What is the voltage reading of your 12v battery after sitting over night? (Method Here) Do not know the car was purchased from Toyota as previously owned vehicle. Do not know the reading of the 12v battery which I assume that this battery that is being spoken of is for the electric motor.

    Have you had your alignment checked? Any pulling or abnormal tire wear? No. The car does wander on the highway but no abnormal tread ware.

    - Are you using the factory tires and wheels? If not, please indicate tire make, model and size (e.g. Goodyear Assurance Fuel Max 185/65R15). Yes we are using the OEM rims with Michelin Harmony 185/65/15.

    - What are your tire pressures? 42 Front 40 Rear

    - Make, model, year, engine and transmission of previous car? (e.g. 08 Honda Civic Si 2.0L 4 cylinder, manual transmission) What did you actually get on the same trips/commute? (Please give us actual numbers, not EPA ratings.) 1995 Toyota Corolla 1.6 liter 5 speed manual transmission. Was getting about 50-55 MPG

    - How are you trying to drive (e.g. trying to stay in electric only?) and how hard are you braking? Trying to drive as easy as possible with out hard take offs and try to stick close to the posted speed limit. I brake very easy and not wait until the last minute to start slowing down.

    - Are you "warming up" the ICE (internal combustion engine) by letting it idle after powering on? No

    - Are you driving using D or B mode? I do not know. Do not know how to check what mode the car is in.

    - HVAC settings? Are you using the heater, AC, auto mode, etc.? If using auto, what temp is it set to? Heater is set for auto and the temp is usually set between 22c-23c and the blower fan is usually set to medium or just under medium.

    - If reporting a mileage drop, did anything significant change on your car (e.g. accident, hit a curb or big pothole throwing off alignment, oil change/other maintenance/repairs, changed tires or wheels, etc.) or your commute? Changed spark plugs w/ NGK Iridium, oil and filter change (Had the oil flushed on last oil change), New air intake filter. Nothing else has changed.
  16. fotomoto

    fotomoto Senior Member

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    IMO, getting over 50mpg in the winter in Canada is a pipe dream for all but the most ardent hyper-milers.
  17. cwerdna

    cwerdna Senior Member

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    Just to be clear here, are you specifying miles per Imperial gallons or US gallons. Imperial gallons are meaningless to those in the US.

    Per Compare Cars Side-by-Side, the 06 Prius (after adjustment) is rated at 46 miles per US gallon combined. My lifetime average on my Prius after >61K miles is ~45 mpg, used to be 46 (long story as to why it's lower now).

    I find it unlikely that your 95 Corolla got 50-55 mpg in the same conditions and same drives. The EPA rating on it was 27 mpg combined.

    As for D or B, we're talking about the shift position as the "combination meter". As you shifting into D or B?

    As for using auto and all, well, that's part of your problem. I almost never use auto. See my notes at http://priuschat.com/forums/gen-iii...mileage-gets-worse-in-winter.html#post1411488 about better heater management. You could be causing the ICE to run unnecessarily to requested provide cabin heat.



    Agree.
  18. ursle

    ursle Gas miser

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    Ding,ding,ding
    I put some "different" manufacturers plugs in my '06 and my mileage was in the low 30's, put the oem's in and went back to 53+, one of the new plugs went bad, didn't throw codes, good practice for putting in an upper strut bar(tearing apart the windshield wiper apparatus;)
  19. bisco

    bisco cookie crumbler

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    you're getting 47 in summer and wanting 50 or better. but it may have more to do with your driving habits than anything else. a lot of people here get around 47 due to heavy foot, short trips and etc.
  20. 06_PriusDriver

    06_PriusDriver Junior Member

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    My 95 Corolla did in fact get 50-55 MPG. That is no lie my friend. Anyway I use D mode for driving. Does the mode make a difference?? Also I did read your note about the auto setting for the heater and that is the next thing I am going to change the next time I go out. As for the 12v battery I am almost sure that Toyota tested all that while it was in for service back in the summer and everything checked out fine according to Toyota. But who knows maybe something changed since then and the battery has gotten weak. I will be looking into that as well.
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