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Hesitation

Discussion in 'Engine, Transmission/Axle & Driveline/Axle' started by ShadowLord, Nov 15, 2016.

  1. ShadowLord

    ShadowLord Member

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    I have a 1996 4.9 E4OD F-150 that has a hesitation on acceleration. My problem appears when I'm taking off from a stop to about 30-40mph and then is fine. Although it only happens randomly. Not every day. After I get going it usually won't happen again until a week or two goes by. Has 140,000 miles. TPS put on last year along with a new IAC. Think it could be spark plugs, fuel pump should be good as it happens on either pump. Any ideas?
  2. Action

    Action Moderator Staff Member Respected Member

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    Typically the description you are giving is a lean misfire. It may be random due to a lot of things like
    Throttle position
    Humidity
    Ambient temperature
    Engine fuel charge temperature

    Know that the electronic engine controls are designed to create the leanest fuel charge possible with out drivability issues. If running correctly the system is always running at the better edge of unacceptable.

    With that start with known items first -
    Maintenance like filters and spark plugs should be done if that service is behind/ Read owner's manual for interval and if you are close change anyway
    If the CE light is on, pull the codes.
    Next would be high suspect areas:
    Vacuum leaks, vacuum hoses connected, air intake system leaks (In front of the throttle body)

    A suggestion would be the O2 sensors. (Up and down stream) Even if no CE light is on these wear out. At the mileage you have they could be near the end of their life and not reporting signals to the computer fast enough. Creating a too lean or too rich condition. (You are not going to feel a too rich condition.)

    Kind of long and yet it is a good read. http://www.obdii.com/articles/Replacing_Oxygen_Sensors_Preventive_Maintenance.html

    Do report back if you fix the concern or if you are at a loss.

    >>>>>>>>>>>>>>>>>>Action
  3. ShadowLord

    ShadowLord Member

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    The problem has only further progressed lately. It did go away after I posted this a year ago, but is back again. So I am going to change the spark plugs and wires as I have no idea when they were last changed as I am the 4th owner. I will report back.
  4. Dominick 1

    Dominick 1 Well-Known Member Respected Member

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    Check your throttle body mounting gasket
    they split in the center
  5. ShadowLord

    ShadowLord Member

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    I did change the spark plugs today as well as the wires. It idled better, and seemed to run smoother overall. I didn't get a chance to take it down the road as I didn't get done until late and just took it to the end of my driveway. I will report tomorrow on it. My old plugs had deposits built up on most of them. One of them even had some carbon it appeared to be blocking the electrode and the top piece. Meaning that cylinder wasn't firing at all. My question is-Wha causes the white deposits I seen? I added fuel additive last week- But there's no way it caused it that quickly? It also does use some oil, although most of it is because of a leaking valve cover gasket
  6. Dominick 1

    Dominick 1 Well-Known Member Respected Member

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    http://www.onallcylinders.com/2012/12/20/reading-101-how-to-read-your-spark-plugs/
  7. Action

    Action Moderator Staff Member Respected Member

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    "My question is-Wha causes the white deposits I seen? I added fuel additive last week- But there's no way it caused it that quickly?"

    Light colored deposits are from incomplete burning of the fuel. Or engine operating too cold. Or oil leakage. Or replacement interval of spark plugs extended too long.

    There are chemicals in the fuel that will leave deposits and the quality of the fuel is an impact on that.

    >>>>>>>>>>>>Action
  8. ShadowLord

    ShadowLord Member

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    Ok, so replacing the plugs definelty helped with power. No more hesitation. But, it still has a moment where it cuts power off. What I mean is I step on the throttle, keep my foot in the same exact position on a straight away, and all of a sudden, it's gets a boost of power. Like the acceleration it should have. I don't understand why this happens unless the TPS is going bad? Again...
  9. Action

    Action Moderator Staff Member Respected Member

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    Is CEL off? (If on pull codes?)
    Air and fuel filters replaced in the last 12 to 18 months?
    If yes to the above get & post engine vacuum reading at idle on warm engine

    When were the oxygen sensors replaced?

    >>>>>>>Action
  10. ShadowLord

    ShadowLord Member

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    There is not CEL, fuel filters were just replaced a month ago. Air filter has been about 2 years, but only 12K miles. I have no idea about the oxygen sensors. I don't have any way to measure vacuum at idle. But it does idle smooth when warm
  11. Action

    Action Moderator Staff Member Respected Member

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    The oxygen sensors send signals to the processor about fuel mixture. (is it too lean, or too rich) This is done a fraction of a second basis. Oxygen sensors wear like spark plugs. After so much wear the signal becomes slow back to the processor. They still pass a prove out test however the signal because they are still working. And the signal is too slow for the processor to make correct adjustments to the fuel mixture. This is especially true when the throttle is being moved. (And most of the time the throttle is moving)

    Replacing the oxygen sensors at 100,000 miles is necessary to restore that signal speed back to the processor. With the mileage you have you are well past that point.

    Smooth idle on warm engine is good. However a small vacuum leak or un-metered air to the engine is an issue and the engine is always running lean. Couple that with weak O2 sensors and the engine never gets the fuel air mixture correct except for idle and high speed operations. Idle can be lean and the engine doesn't car that much because there isn't a load. At high speed the computer is dumping nearly full rich because the engine is higher rpm and vehicle speed is higher.

    >>>>>>>>>>>>>>>>Action
  12. ShadowLord

    ShadowLord Member

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    Ok I will check into that and report back when I can
  13. ShadowLord

    ShadowLord Member

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    If the MAf sensor is dirty? Could it also effect when the accelerator decides to respond to the change? Being that it measures the air going in also? (ASking bc this would be an easy fix and cheap to buy cleaner for it)
  14. Action

    Action Moderator Staff Member Respected Member

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    May be. And a poor running condition would be present under all conditions not intermittently. I don't think that is your issue.

    Cleaning does have some risk if not done correctly. And not expensive to do.

    >>>>>>>Action
  15. Dominick 1

    Dominick 1 Well-Known Member Respected Member

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    Unplug the MAF sensor and see how it reacts
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  16. ShadowLord

    ShadowLord Member

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    Ok. So upon my research I have found out there are three different per say, O2 Sensors. I've read theirs two coming down from the manifold and 1 on the cat converter. Would the two on the manifold be causing my issues, or the 1 on the cat? The problem seems to present itself when the engine begins to warm up (10mins of driving or so). I step on throttle, nothing happens, it maintains speed, but won't accelerate, then after 10 second to a minute it will eventually begin to accelerate. Could this be something else? I have no CEL?
  17. ShadowLord

    ShadowLord Member

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    It also doesn't matter the speed im going. It happens at 15 mph and 55 mph
  18. Action

    Action Moderator Staff Member Respected Member

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    I am surprised there isn't 4. And no matter, all O2 sensors should be replaced at 100,000 miles. With 140,000 miles a year ago on your ride all of them are suspect as far as doing the job as intended. Like spark plugs replacing some is not the standard. Replace them all. They can be purchase for $25 to $30 each.

    There are a several possibilities of bad parts based on your symptoms. Working from the known to the unknown is far easier than guessing. Working from maintenance to repairs is better as well.

    With no CEL the assumption would be non-electronic parts. O2 sensors will NOT trip a code unless they are not working. If they work slow and give inaccurate (slow) information the CEL will not light up.

    Other non-electronic issues -
    Small vacuum leak(s)
    Intake system gummed up with varnish
    Filters that need to be replaced
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  19. ShadowLord

    ShadowLord Member

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    After further research today,(as the oxygen sensors are about $75 for all three and a pain in the butt to get to) I looked for other possibilities. Sense the problem only occurs when the engine is warm, I'm leaning towards an injector failure? Mainly because it happens when it is warm, and I noticed the engine surges up and down at idle when it's warm also. My truck, as I posted in another thread also has a problem with the RPM's staying high when I shift and when going down a hill the truck speeds up intermittently without touching the pedal, (sometimes only in bursts-like 1-2mph or it opens the throttle completely to red line in 1st and 2nd gear). So, could these two problems concurrently happening, be the result of bad injectors?
  20. Dominick 1

    Dominick 1 Well-Known Member Respected Member

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