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Reducing oil dilution in priusII

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by epoch_time, Mar 27, 2018.

  1. epoch_time

    epoch_time Active Member

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    I've been using torque apk for many years continously.
    Short Term Fuel trim is one of the guages I keep my eye on.
    I've seen short term fuel trim as high at -19 (19% added fuel) durring engine warm up (86-150 degrees F).
    My prius has 98k miles with orignal maf,plugs,injectors and I have never cleaned the maf yet.
    My fuel trim might be higher than yours if you have changed maf, plugs or injectors.
    To reduce oil dilution with unburnt gasoline I drive my prius in braking gear (B mode) while the engine is warming up.
    When releasing the accelerator pedel in B mode durring warm-up (at speeds above say 25mph) the injectors stop injecting gasoline which normally only happens once the engine is warmed up (150 F and above and in D=drive mode).
    But durring engine warm-up injectors don't stop injecting gasoline while in D (drive) gear unless the engine is warmed to 150 F and above.

    If I happen to get stuck at a red traffic light while in B (down hill engine braking) mode/gear the gasoline engine (ice) will not stop running. So I will put the transmission back to D (drive) mode to let the engine stop running while at a red light.
    If you left transmission in B mode while at a red light and engine is under 150 F the fuel trim will remain high and the engine will not stop running and injecting extra fuel thus diluting the oil.

    Also I do not use the cabin heater till the engine is warmed above 150 F. Running the heater durring warm up cycle will keep engine running while stopped at a red traffic light (regardless of selected transmisson gear when engine temp is below say 145F) injecting extra gasoline which doesn't all get burn't resulting in more oil dilution.

    I've always used mobil 1 ep 5-w30 synthetic since the prius had 2500 miles.
    Without this special warm-up procedure I would start hearing slight engine noise 2500 miles after each oil change.
    Doing this special warm-up technique I have gone up to 5500 miles on an oil change and not heard any engine noise.

    I also no longer smell gasoline on my oil dip stick.
     
    #1 epoch_time, Mar 27, 2018
    Last edited: Mar 27, 2018
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  2. Aaron Vitolins

    Aaron Vitolins Senior Member

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    Interesting. Does your car burn oil?
     
  3. valde3

    valde3 Senior Member

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    Fuel trim value of -19% means that control unit is REDUCING the injected fuel by 19%.

    If you have fuel trim value that low and fuel dilution of oil perhaps you have a leaking fuel injector?
     
    #3 valde3, Mar 27, 2018
    Last edited: Mar 27, 2018
  4. epoch_time

    epoch_time Active Member

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    I mean to say its short term fuel trim that I'm talking about.
    Neg short term fuel trim on prius genII (displayed with torque apk) is adding fuel.
    My prius burns about 8 ounces per 5k miles
    and my st fuel trim is high (neg.19) only durring warmup. Not after engine is above 150F.

    I should also say that oil dilution was not a problem with the SM rated oil (no engine noises heard with SM oil) oil still smelled gassy but no engine noise.. But when the government made reductions of zinc and phosporus (SN oil) then I started hearing engine noise after only 2000-2500 miles on mobil 1 5-w30 synthetic oil. No more engine noise using special warm-up technique.

    We also have prius genIII never had any fuel dilution on our prius genIII.
    54k miles (genIII) using mobil 1 0-w20 synthetic.
     
    #4 epoch_time, Mar 27, 2018
    Last edited: Mar 27, 2018
  5. valde3

    valde3 Senior Member

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    Where did you get that info? Of course it’s possible that there’s a coding error in torque app. But that sounds unlikely. In that case you should check the fuel trim value with something else as figuring out which way the ecu is trying to correct the fuel trim with cold engine is key in figuring out this problem.

    Normally positive value of fuel trim means that ECU is ADDING fuel to compensate for LEAN condition. And a negative value means that ECU is REDUCING fuel to compensate for rich condition. Short term and long term fuel trim values work the same way. Short term and long term fuel trim values are just added together to get total fuel trim value that’s then used to change the amount of fuel injected.

    Looking at Gen 2 Prius manual for P0171 and P0172 (codes for rich and lean) it operates exactly the same by setting a lean code if total fuel trim reaches +33% and a rich code if total fuel trim reaches -30%.

    Fuel trim being negative (ecu REDUCING fuel) only when engine is cold could be a fuel injector that only leaks when cold.
     
    #5 valde3, Mar 27, 2018
    Last edited: Mar 27, 2018
  6. epoch_time

    epoch_time Active Member

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    Just as you say watching the st fuel trim when engine is cold to determine which way fuel is added or subtracted is how I know is neg. adding fuel when cold as shown on torque apk.

    If you carfull read my orignal post you would see I'm specifically talking engine cold conditions.
    I've had torque apk running for probably 6 years now. continously I dont leave home without torque apk.

    I agree its not logical that neg st fuel trim is adding fuel (torque apk)but It is.
    I is not logical hv battery regen charging is also shown as a negative number on torque apk, scanguage, etc.

    All backwards. but it doesn't take a rocket scientist to figure out which sign is what.
     
  7. valde3

    valde3 Senior Member

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    Sorry but I still don’t know how you determined that negative short term value is adding fuel? Richening the mixture (adding fuel) for cold engine is already in the fuel map so that won’t affect the short term fuel trim. One sure way would be to inject extra fuel into the idling engine (for example brake cleaner) and watch the short term fuel trim number. If the number goes to negative then negative is reducing fuel.

    Yes I did get that the problem only happens with cold engine. That’s why I did say that if the ECU is reducing the fuel amount with cold engine then maybe you have a fuel injector that’s leaking when cold.

    Actually charging the battery with negative value and discharging it with positive value is the logical way.
     
  8. epoch_time

    epoch_time Active Member

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    Over 7 years of prius chat posts.
    I've seen many posts over the years reporting this neg st fuel trim (when expecting pos. numbs) durring warm-up from perfectly running prius's / owners questioning why is it backwards.

    The many posts were not regarding problems with there prius but mearly observations.

    Myself baffled with this backward sign-age (back approximately 2011) I did an interrnet search and found there were other car manufactures that reported backward fuel trims but warned technicans so they could interpet results appropiately. I don't remember which other manufactures they were but toyota wasn't one of them listed.
    But still have been many posters reporting the backwardness of the fuel trim.
    I believe the long term fuel trim to have the correct sigh-age cause it follows what is expected.

    Maybe there could be different software/firmware with genII years 2004-2009 but I dought it.
    I also watch injector time durrring warm-up 5ms (-3 stft) = 25-30mgh. After warm-up 5ms injector open (0-1 stft) = 55-60 mph. fuel trim only hits -19 going downhill no accelator pedal and traveling 40-60 or more mgh and engine temp below 150F. I also watch air to fuel ratios look (at all times hot or cold) great mostly 14.5:1 (suspiciously to good).

    After warm-up stft goes neg climbing hills. goes positive decending hills and follows injector timing.
    The inclineometer (I think it is the gas fuel float) adds fuel (neg. stft) for climbing overpasses and subtracts fuel (pos stft) while decending (stft).

    I've never had any codes set on my prius. I always get 50+mpg and my drives are 99% city driving.

    Hope this helps.
     
  9. dolj

    dolj Senior Member

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    I'd like to say hi and welcome to @Erik Owens, and thanks for taking an interest in the Gen 2 forums.

    I was wondering if you could review this thread and may be add any comments about how the fuel trim (both long and short) data points work and what the values mean, which I take have a range of -30% to +33%.

    It is that the interpretation that epoch is giving based on observation does not gel with me, but, then again, I am clueless about this whole area, so I, for one, would like something concrete to add to my knowledge.

    Any input from someone who knows how to interpret the FT data would be welcome.
     
    #9 dolj, Mar 28, 2018
    Last edited: Mar 28, 2018
  10. valde3

    valde3 Senior Member

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    I tried to find any thread that talks about fuel trim being backwards on Torque app but couldn’t. Could you post a link?

    You’re misunderstanding a fuel trim a bit. How the system works (simplified) is that first the control unit takes into account all the other sensors and calculates how much fuel engine should need and then use air fuel ratio sensor (and/or oxygen sensor) to correct the injected amount of fuel a bit (a lot in your case with cold engine). Fuel trims are just based on the readings from exhaust sensors.

    System needing a lot of correction when engine is cold indicates that there is a problem. And unless the Torque software is showing the fuel trim number backwards negative value is showing that it’s reducing the amount of fuel.

    Code will only set if the fuel trim reaches -30% or +33%. So that’s why you’re not getting a code. But many say that fuel trim values of more than 10% positive or negative should be investigated and you do have lot more than that. And the fuel trim value being off only on a particular situation is even more indication of a problem.
     
  11. Erik Owens

    Erik Owens Member

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    Give me a day to bone up. I work all day and then get on the site. Give me a day and Ill print this out and read over and try to get back to you later today or tomorrow.
     
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  12. wjtracy

    wjtracy Senior Member

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    Yes I believe Gen2 had more loose cylinder clearances which results in several percent gaso dilution. That's why going to 0W-20 is not a great idea for Gen2, and why drain interval is more important (though I still procrastinate)..

    Some like the idea of 0W-40
     
  13. valde3

    valde3 Senior Member

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    Fuel trim going to -19% or (19% if inverted) with cold engine tells that this gen 2 Prius does have some problem. The problem can also affect the oil dilution so correcting it should be the main priority.
     
  14. epoch_time

    epoch_time Active Member

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    I was using a scanguage back around 2010 is also shows stft negative while warming and other times when additional fuel is injected.
    Again long term fuel trim shown on scanguage and torque appear to show the correct sign.
    Its only the short term fuel trim (stft) showing the wrong sign on scanguage as well as torque apk.
    Back 2010 I was using scanguage my prius probably had only 15000 miles probably less.
    Over the years I have watched stft increase only durring engine warm-up say 1 or 2% per year.
    While long term fuel trim has remained stable over the years.
    Yes I do have a problem (stft sometimes -19%). GenII prius's have a history of oil dilution I thiink mostly city driven under 10 miles per trip where the engine rarely reaches operating temperature. .
    My genII prius appears to have 180F thermostat and 183F is the normal warmed-up engine temperature and it takes about 10 miles with outside temperature 40-50F to reach operating temperature.
    Our GenIII seems to have a 190F thermostat and also takes about 10 miles to reach operating temperature (say 192F).
    My wife drives the GenIII. So I only have 10 or 20 hours of torque apk operating on the GenIII but oil dilution is not a problem like with the GenII.

    Its very important that engine oil reach operating temperature (extended drive or at least 10 miles) so that gasoline in the oil will have a chance to be burned off (evaporated).

    Valde3 How many hours of operation on your prius have you; while watching short term fuel trim?
    How many hours of (your personal prius) driving while watching long term fuel trim?

    I have thousands of hours watching stft. Dont you thing I might posibly know what I talking about?

    The internet search I did years ago where I found other car manufactures reporting negative instead of positive values for fuel trims was not specific to torque apk or scanguage but specific to certain manufactues ecu's.

    I think we are geting off topic. This tread in specific to reducing oil dilution. It should have nothing more to do with Negative or positive fuel trim ecu coding errors.

    My results are long lasting oil (no more gasoline smell on my dipstick), long lasting engine (no more engine noise on older oil). And oil dilution on genII prius is a known problem.

    And yes there is a problem with my stft durring warm-up. however after I fix the fuel trim problem I will continue to use my special warm-up procedure as it definately extends oil quality and reduces oil dilution.

    I was hoping Anyone with oil dilution may benifit from this post (unless there check engine light is on) there is other problems .

    Also mobil 1 oil company considers frequent drives less than 10 miles duration as severe service duty on oil. And says severe service duty of oil requires earlier oil changes.

    Hope someone gets benifet from all this.
     
    #14 epoch_time, Mar 28, 2018
    Last edited: Mar 28, 2018
  15. Mendel Leisk

    Mendel Leisk Senior Member

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    Just to clarify, by "oil dilution" you mean gas getting into the oil?
     
  16. epoch_time

    epoch_time Active Member

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    Yes Gasoline getting into oil.
     
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  17. epoch_time

    epoch_time Active Member

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    This discription from your manual follows exactly what I'm stating. Negative value adds fuel. Positive reduces fuel.
    Example should my fuel trim reache -30 it will set a rich fuel code. Meaning to much fuel is being added.

    Durring engine warm-up any car (any model) fuel should be rich condition (adding fuel for faster warm-up). genII prius shows this as negative number (my case under certain conditions -19) should my prius reach -30 according to your prius manual will set error code rich fuel (exacty right too much fuel being added). I do not see your confusion?

    .
     
  18. Erik Owens

    Erik Owens Member

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    This black and white out of our new car features for a 2004 which is the exact same design you have. Deceleration in “B” Range While the vehicle is being driven with the shift position in the B, and decelerates, the wheels drive MG2, causing MG2 to operate as a generator, charge the HV battery, and supply electrical power to MG1. Accordingly, MG1 maintains the speed of the engine and applies an engine brake. At this time, the fuel to the engine is cut.
     
  19. Erik Owens

    Erik Owens Member

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    Plus I wouldnt be looking too hard in to data from an app and bluetooth adapter. I know it is helpful but you get what you pay for. I use an actual Techstream software and decent operating system on a gaming laptop and I still have to select the parameter for fuel trim and put it in its own little queue so it will speed up the refresh time of the data being received from the ECM which is still lags by a couple of seconds.
    Plus no matter what kind of vehicle you own with an internal combustion engine you are going to get that oil dilution. One of the many reasons we change oil. Notice how I said many of the reasons. There is detergent in the oil, lubricity, viscosity factors, etc.
    I fix vehicles and if you havent set codes and your fuel trims are good at idle when engine is warmed up and when at 2500 to 3K RPM then its not even lighting the Air fuel ratios (fancy O2 sensors) off to affect fuel trim. Plus to add that there was a comment that fuel is over used to heat up the engine, catalytic converter to convert to clean inert gas. Also you are using an Atkinson cycle engine which can, with that CVT and VVT vary all sorts of factors. As long as your MPG is good, your tail pipe isnt super sooty, and you are not burning oil like crazy and no noise I cant help too much on this front guys.
    Its like asking a Navy Seal best how to disarm someone,....they sneak out of site to KILL effectively. Thats what a technician does which is look at the data that is important to fix broken items or improve performance issues correctly and quickly.
    Hopefully I didnt wast too much of your time giving you this explanation. I just want folks to enjoy their vehicles and collect failure issues which this site and multiple sites produce.
    Hell I even fixed a car, mainly with my training and experience and diagnostic method, but it helped to know that multiple people in multiple areas in certain date models of a Prius are having an exact issue.
    If you would still like a huge verbatim explanation of fuel trims I can get that for you as well.
     
  20. Mendel Leisk

    Mendel Leisk Senior Member

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    What about what gets caught in an Oil Catch Can? Interesting brew. This was the harvest December 30th, 2017, 2380 kms post install:

    IMG_8097.JPG

    And the same stuff, this morning, settled out:

    IMG_8417.JPG
     
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