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Nissan Sentra 08 (B16) Running Rich

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This topic contains 17 replies, has 2 voices, and was last updated by Nightflyr * Richard Kirshy 8 months, 3 weeks ago.

  • Creator
    Topic
  • #895507
    Harry
    Harry
    Participant

    Hello Everyone
    Have being facing rich condition for my car for the past one year and have done tons of repair stuffs that never seems to change the rich condition.
    Please check below for the details and give me your thoughts, suggestions and repair ideas if any.
    Am a diyer person though!

    -Vehicle
    Nissan Sentra 2008 2.0l Petrol Base Model (CVT Transmission)

    -Problem
    Car running rich so much that hurting my purse.
    Plug in obd and fuel trim reads stft-8 and lft -10 and get worse at cruising speeds (ie stft -15 -20 bouncing around with ltft -10, -18)
    To my surprise car pass emission test with the obd emmission test section.
    Can give you shots as per requested on any parameter you want to see in the obd output.

    -What done so far
    Changed air filter assembly; was fitted with short ram air intake from the buyer i bought it from earlier
    Changed oxygen sensor
    Changed maf sensor
    Changed cat converter (Though no problems or associated trouble codes earlier)
    Check and confirm pcv working (Cleaned and make noise when shake)
    Changed head gasket (Had a blown head gasket earlier which is fixed now, car was overheating with coolant bumbling)
    Changed engine oil and filter
    Changed fuel pump assembly (Thought was faulty fuel pump pressure issue)
    Changed ECM (Thought was faulty)

    -Suspect
    Spark plugs (Appears worn out) carbon deposit
    Not replaced it since November, 2018
    But can a spark plug cause this?
    I dont want to go ahead replacing it without being technically sure its the absolute problem, have done so much this as per above things done.

    HELP!!!!!!

Viewing 15 replies - 1 through 15 (of 17 total)
  • Author
    Replies
  • #895509
    Nightflyr *
    Richard Kirshy
    Participant

    I might first suggest you try a ECU reset.
    Disconnect both the positive and negative from the battery and short them together for several hours or overnight( just to be sure).
    Reconnect the battery.
    Let it warm up for ~10 minutes.
    Then take it for a reasonably long drive to set all the ready monitors.
    Then check your trims again.

    #895512
    Harry
    Harry
    Participant

    Have done that couple of times
    It pick up right back in a couple of minutes into negatives stft & ltft
    Btw have replaced ecm as well, forget to add that.

    #895515
    Nightflyr *
    Richard Kirshy
    Participant

    In that case you may want to test for leaking injectors.

    #895519
    Harry
    Harry
    Participant

    That has being also done already.
    Injectors are good, took opportunity to even clean and refix it when the test was conducted earlier.

    #895524
    Nightflyr *
    Richard Kirshy
    Participant

    Might check the coolant temp sensor.
    It does not send a CEL, but a faulty one will fool your ECU into thinking the engine is running hot, so it increases your air/fuel mixture to cool things down.

    Also check that timing and#1 TDC are correct

    #895528
    Harry
    Harry
    Participant

    To the best of my knowledge ect works well, being monitoring with the obd when am driving around. Operating between 156F to 208f of course at cold start dumping in much fuel which makes the car run rich for a moment before the turns to operating temperature.
    Btw with your take, ect fooling the ecm should rather take out fuel when it sense the car is running hot but not adding ( run rich). Ecm run rich at cold start not operating temperature.
    Stand to be corrected though.

    Also how do I check if the timing is correct or #TDC
    Can you educate me a bit here ?

    #895529
    Nightflyr *
    Richard Kirshy
    Participant

    To begin with the engine temp sensor and the coolant temp sensor are different.

    The coolant temperature sensor, also known as the coolant temperature switch, is an engine management system sensor that is used to monitor the temperature of the engine’s coolant. Most coolant temperature sensors operate using electrical resistance to measure the temperature of the coolant. This signal is then sent to the computer so that changes can be made to the engine’s timing and fuel calculations for optimal performance, as engines require more fuel when they are cold, and less fuel when they are fully warmed up. The computer will also scale back engine performance settings if it detects that the engine temperature is too high, in order to protect the engine from possible damage due to overheating.

    Because temperature plays such a vital role in engine performance calculations, any problem with the coolant temperature sensor can quickly translate into an engine performance issues. Usually a problem with the coolant temperature sensor will cause a few symptoms that alert the driver of a potential problem that should be thoroughly inspected.

    One of the first symptoms associated with a problem with the coolant temperature sensor is poor fuel economy. If the coolant temperature sensor goes bad it can send a false signal to the computer and throw off the fuel and timing calculations. It is not uncommon for the coolant temperature sensor to fail and send a permanently cold signal to the computer. This will cause the computer to think the engine is cold, even when it is not, and as a result will use more fuel than necessary. This will reduce fuel economy, and may hinder engine performance.

    Another symptom of a problem with the coolant temperature sensor is an overheating engine. The coolant temperature sensor can also fail in a manner that causes it to send a permanently hot signal. This can cause the computer to incorrectly compensate for a lean signal, which can result in overheating, and even misfires or engine ping.

    A coolant temperature sensor (CTS) (also known as an ECT sensor or ECTS (engine coolant temperature sensor) is used to measure the temperature of the coolant/antifreeze mix in the cooling system, giving an indication of how much heat the engine is giving off. The sensor works with the vehicle’s ECU, continually monitoring the coolant temperature to make sure the engine is running at the optimum temperature.

    To get an accurate reading of the current engine temperature, the ECU sends a regulated voltage to the CTS. The resistance of the sensor varies with temperature, this is how the ECU can monitor temperature changes. The ECU uses this reading to calculate the coolant temperature, and from there adjusts the fuel injection, fuel mix, and ignition timing, and controls when the electric cooling fan is switched on and off. This information is also used to send an accurate reading of the engine temperature to a gauge on the dashboard.

    Some vehicle ( certain Nissans ) are equipped with both sensors, one to handle the dashboard function while the other works in conjunction with the ECU for engine management.

    Btw with your take, ect fooling the ecm should rather take out fuel when it sense the car is running hot but not adding ( run rich). Ecm run rich at cold start not operating temperature.
    Ummmmm, think you need to read this.
    By changing the amount of fuel in the mixture, you are changing the types of collisions that can occur. And it’s not exactly straight forward, but some molecules are better at exchanging energy with others. To make the fuel molecule fall apart, they need to collide with other fuel molecules with some energy of with other oxygen molecules with more energy. <font color="red]If you add more than the usual amount of oxygen (run lean), you also need to make that oxygen hotter[/color] so the molecules have more energy when they collide and can make the fuel vibrate hard enough to fall apart. Conversely, if you run fuel-rich, you have more fuel molecules that can collide with one another and fall apart, [color=red”>but fewer oxygen molecules for them to combine with and give off heat. This (and some other effects) makes the final flame temperature lower.

    Can you educate me a bit here ?

    https://www.youtube.com/results?search_query=check+if+the+timing+is+correct
    https://www.google.com/search?client=firefox-b-1-d&q=check+if+the+timing+is+correct

    https://www.youtube.com/results?search_query=check+%231+TDC
    https://www.google.com/search?client=firefox-b-1-d&ei=TUH5Xbn0E8-e5gKokrmwBw&q=check+engine+%231+TDC&oq=check+engine+%231+TDC&gs_l=psy-ab.12…9292.12658..14366…0.2..0.106.666.6j1……0….1..gws-wiz…….0i71j33i10.HAy4LnFNas8&ved=0ahUKEwj5zrilyb3mAhVPj1kKHShJDnYQ4dUDCAo

    #895542
    Harry
    Harry
    Participant

    Great submission and write up
    As said earlier ect is doing fine and am absolutely convinced is not the culprit.

    With Tdc and timing, you basically want to verify if timing is jumped or in a wrong position; thought as much earlier.
    Timing is fine, when head gasket was being replaced we took the opportunity to align timing belt markings (dark spots) to camshafts stamped nodes. Engine start and run better afterwards; so timing is not a problem here.

    Below is the link of obd output for your perusal

    Do @nightflyr
    You are not convinced the spark plug will be the reason right?

    #895544
    Nightflyr *
    Richard Kirshy
    Participant

    I’m not convinced of anything specifically without seeing and testing.
    I only offer possible causes to look into.

    I’ll site you an example:
    A friend brought his vehicle over claiming the engine had a shake / vibration when idling.
    Personally I didn’t feel it or see it while watching the motor.
    But he pointed out if you watch the radio antenna you could see it vibrate.
    True enough you could but it was so minor many wouldn’t believe it a problem and the vehicle rode and drove extremely well being 19 year old and had no codes and idled better than many new cars.
    But it seemed to really bug him.
    He had replaced pretty much everything you can imagine, plugs, wires, distributor, MAF, all filters, new air intake, all new vacuum lines, the list was quite extensive.
    He also took it and had the system smoked to check for leaks.

    Scratching my head and beginning to believe to believe this just may be the workings of a 20 year old car.
    I hooked up a scanner to it and noticed fuel trims were a bit high, but nothing really unusual at idle, but went higher as you increased rpm.
    Not quite the trail to a vacuum leak or injector issue I would think.
    Went and hooked up my smoke machine and could fine no leaks (which didn’t surprise me considering there were no codes )
    Well with everything being replaced under the hood I decided to have a look in the rear.
    Now to my surprise after awhile, I stumbled across a crack in the top half mounting flange of carbon canister where the purge valve mounts.
    If you were to look at any angle other than directly perpendicular you would never see it.
    It was cracked due to the mounting screws rusting and swelling that cracked the mounting flange.
    Installed a new canister and purge valve and any sign of vibration was gone.

    #895548
    Harry
    Harry
    Participant

    [quote=”nightflyr” post=204053]I’m not convinced of anything specifically without seeing and testing.
    I only offer possible causes to look into.
    [color=red]Sure, i understand this perfectly. But distance is a barrier. Am leaving in Ghana, africa.
    So persist in just giving me the possible causes as i look through all of that.
    [/color]
    I’ll site you an example:
    A friend brought his vehicle over claiming the engine had a shake / vibration when idling.
    Personally I didn’t feel it or see it while watching the motor.
    But he pointed out if you watch the radio antenna you could see it vibrate.
    True enough you could but it was so minor many wouldn’t believe it a problem and the vehicle rode and drove extremely well being 19 year old and had no codes and idled better than many new cars.
    But it seemed to really bug him.
    He had replaced pretty much everything you can imagine, plugs, wires, distributor, MAF, all filters, new air intake, all new vacuum lines, the list was quite extensive.
    He also took it and had the system smoked to check for leaks.

    Scratching my head and beginning to believe to believe this just may be the workings of a 20 year old car.
    I hooked up a scanner to it and noticed fuel trims were a bit high, but nothing really unusual at idle, but went higher as you increased rpm.
    [color=red]Just as mine, trim increase at higher rpm. With this was it negative or positive rpm?
    With mine, at idle when i introduce vacuum leak by removing the dipstick, fuel trims goes fine (ltft -3, stft 2)[/color]
    Not quite the trail to a vacuum leak or injector issue I would think.
    Went and hooked up my smoke machine and could fine no leaks (which didn’t surprise me considering there were no codes )
    Well with everything being replaced under the hood I decided to have a look in the rear.
    Now to my surprise after awhile, I stumbled across a crack in the top half mounting flange of carbon canister where the purge valve mounts.
    If you were to look at any angle other than directly perpendicular you would never see it.
    It was cracked due to the mounting screws rusting and swelling that cracked the mounting flange.
    Installed a new canister and purge valve and any sign of vibration was gone.[/quote]
    [color=red]I see, i know if i persist in looking and i dont lose hope with guys around like you, i will nail the problem down sooner than later.
    Because these vehicle has superior fuel economy with others confirming it, but mine is horrible.[/color]

    #895549
    Nightflyr *
    Richard Kirshy
    Participant

    With mine, at idle when i introduce vacuum leak by removing the dipstick, fuel trims goes fine (ltft -3, stft 2)

    Another tidbit of information….
    Might explore the engines crank case ventilation system

    #895576
    Harry
    Harry
    Participant

    Yes
    The crank ventilation system includes the pcv and which items to look at?

    #895577
    Nightflyr *
    Richard Kirshy
    Participant
    #895680
    Harry
    Harry
    Participant

    Replaced the spark plug
    Car still running rich, matter of fact nothing changed.
    Am thinking might be exhaust leak?
    But am confused, vacuum leak should cause positive fuel trim but this one is rather negative trim.

    #895681
    Nightflyr *
    Richard Kirshy
    Participant

    Have you tested the injector flow rate?

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