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Engine straining. Lost power. Poor MPG

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by AG2012, Dec 22, 2014.

  1. AG2012

    AG2012 New Member

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    Hi to you all from the UK.

    You may have heard this question a hundred times before but worded similarly. But I've trawled through the forum and I don't think its been answered correctly yet as all the answers point to something different.

    Basically, about 3 weeks ago I noticed some problems with my 04 Prius. It has 72k miles on the clock. The exhaust was making a farting sound. I have since diagnosed this as a hole in the back box which I promptly replaced. But the real problem is the power.

    When driving in electric mode, the car runs as normal. But when I press down on the gas just a little more to the point where the ICE kicks in, it doesn't give as much power as it used to. For example, in electric mode, cruising at 30mph and achieving 99.9mpg, I'd press the pedal down about half an inch. Where this used to kick the ICE in and show 60mpg+ (with the engine charging the battery and providing power to the wheels), it now shows about 30mpg. When I press the pedal a further half inch, it would normally show 35-45mpg, but now reads 16-25mpg. And when its fully depressed, it used to show 12-16mpg but now barely hits double figures and averages about 6.7mpg. Even on highways when I've achieved 60mph and gently ease off the pedal to maintain speed or really slowly increase, I used to achieve 60-70mpg but now I'd be lucky if it makes it to 40.

    I also noticed that it produces considerably less pulling power than it used to. Almost as if the engine is really struggling, even when gently pressing the pedal and accelerating from 30mph upwards. This is having a large effect on my overall fuel consumption and my ability to not piss normal drivers off. I get so scared that I'm wasting too much fuel that I drive really conservatively now.

    So in essence, I'm asking for help because at the moment, I'm barely achieving 300miles from a full tank where I used to get 450+. My driving habits have not changed at all so it HAS to be the car. Could it be linked to the damage or repair of my exhaust? I doubt it because changing the rear end has made no difference except to stop the farting noise from persisting.

    Thank you all in advance.
     
  2. Easy Rider 2

    Easy Rider 2 Senior Member

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    You need to understand that a LOT of things can cause the engine to be down on power like you describe, so ALL of those "answers" might have been right and you just need to find out which one applies to you.

    And when describing things you have done, using the right terms is really important. "Black box" isn't the right part name for any exhaust component I'm pretty sure.

    If you insist on doing this yourself, realize that guessing and changing parts out often ends up being MORE expensive and time consuming than just taking it to a garage to have it fixed right.

    The most common, easiest and cheapest things need to be checked first:
    Oil level.....seriously
    Intake air filter
    12 V battery health
    Next most likely: Catalytic converter plugged; probably not a DIY fix.

    You should at least have a shop connect a code scanner to it to see if any codes are set.
    There are literally a dozen other things that could cause it too; maybe more.
     
  3. Aaron Vitolins

    Aaron Vitolins Senior Member

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    ^really good advice above^ when was the last time the spark plugs were replaced? Best regards
     
  4. nitteo

    nitteo Junior Member

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    im guessing spark plugs. but like above. sounds like the engine is choking which is caused by:

    not enough air for combustion = clogged air intake

    not enough spark to combust = dirty or dead spark plugs
     
  5. Mendel Leisk

    Mendel Leisk Senior Member

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    Maybe there's a further restriction in the exhaust system, further upstream?
     
  6. AG2012

    AG2012 New Member

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    Hi. Thanks for the replies.

    Easy rider 2 - apologies for using the word BACK box. What I meant is muffler. And this had to be replaced regardless. As I said before, it was making noise and then on inspection I found it had holes in it.

    Aaron - I had the spark plugs changed during my half year service which was approximately 4 months (4000miles) ago.

    Same with the air filter.

    The engine is combusting correctly. But between combustion and power transfer I have noticed there is more lag and the output has significantly decreased. I will be taking it to a garage tomorrow with hopefully some good news. Although as I am tight on funds I hope it is a DIY fix. I seldom trust mechanics with my car as I know the games they play to try rip me off.
     
  7. AG2012

    AG2012 New Member

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    P.S. the oil level is fine. Its half way between both holes on the dipstick.

    Battery will be checked tomorrow but I don't think its that as I had it change 1.5 years ago
     
  8. bisco

    bisco cookie crumbler

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    maybe a bottle of injector cleaner. have you had the codes checked?
     
  9. AG2012

    AG2012 New Member

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    I haven't had the codes checked. I will be going to a garage tomorrow for that.

    I have used injector cleaner as a precaution but to no avail. Didn't think it would either as the fuel is getting to the chamber. It is even revving fine. But the power is lost somewhere after that. I've just been out for a drive and even in town as soon as it switches from electric to petroleum mode, I see the figure drop to 24-29 mpg which is really bad as I normally achieve 45+.

    I know you may be thinking I have a lead foot but I don't change my driving style at all and have noticed this problem very recently. Has anyone else had this problem which they have fixed? Regardless of how many different causes there could be.
     
  10. Mendel Leisk

    Mendel Leisk Senior Member

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    Further on my thoughts above: when the muffler goes, say rusting out or whatever, the next pipe in line, the catalytic converter, and so on, may not be far behind.
     
  11. Data Daedalus

    Data Daedalus Senior Member

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    Here's an idea.......Tyre pressures! Check your tyre pressures carefully all round. It takes just ONE tyre with abnormally low pressure to drag your mpg right down. I suffered a similar problem - rear tyre on the drivers side was leaking - dropped down to 20psi. I had noticed the car was straining to accelerate, was noisier than usual, and was even a bit reluctant to drive along in electric mode. And yes, my mpg went down despite my being careful with the throttle. Pumped the tyre up and the problem literally disappeared. MPG started climbing immediately. And the car was once more effortlessly flying up hills with far less noise. Check your tyre pressures......just a thought. (y)
     
  12. AG2012

    AG2012 New Member

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    Hi. Tyres are fine. 36psi all round
     
  13. Data Daedalus

    Data Daedalus Senior Member

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    Make that 40psi on the front tyres and 38psi on the back tyres. I run this configuration and my Gen II gave me 66.3mpg last summer (UK). Right now (winter), I've got 54.2mpg on the clock. At least, this will help eliminate what the problem is. Oh, and what tyres do you have on the vehicle?
     
  14. Easy Rider 2

    Easy Rider 2 Senior Member

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    If the engine rev's fine but the car won't "go", that pretty much just leaves the transmission.

    While that's possible, transmission failures seem to be rather rare, thankfully, and I'm still betting on an engine problem.

    The sound and feel of these engines is not as directly tied to good output as it is with a conventional one.
     
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  15. edthefox5

    edthefox5 Senior Member

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    Hybrid battery going bad.

    Watch consumption screen for battery behavior.
     
  16. goldfinger

    goldfinger Active Member

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    AG2012, did this poor behavior start when you fixed the muffler (back box)? The ecu could need a few tanks to learn the new exhuast. Also, could the lamda oxygen sensor been damaged during the exhaust work?
     
  17. AG2012

    AG2012 New Member

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    Data Daedalus - I havent changed anything on the car for the past 3 months except muffler. Tyres are the same. This problem started happening BEFORE I fixed the muffler.

    Edthefox5 - no difference in the way the battery charges or discharges.

    Goldfinger- the problem has been there since my muffler has been damaged. All this time, I though it was the damaged muffler which was affecting my mpg but this doesn't seem to be the case as the problem is still there after repair.
     
  18. Easy Rider 2

    Easy Rider 2 Senior Member

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    The CATALITIC CONVERTER might also be damaged......internally.
    A partially restricted exhaust will cause the symptoms you describe.
     
  19. AG2012

    AG2012 New Member

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    I've just checked the battery by doing the secret mode test. It was at 10.7v on a sitting mode. 9.6v in accessory mode.

    But can that actually affect my mpg that bad?
     
  20. Yakoma

    Yakoma Active Member

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    That question is irrelevant. You need a new 12v battery. Get that first, then start your diagnosis over.
     
    dolj likes this.