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HT4100 4.1, 4.5, 4.9 Discussion, does ECU prevent engine braking in Cadillac Engine Technical Discussion; BBOB this is the place How do I close the other posts. Im new to this and got lost. I ...
  1. #16
    CAPTJACK is offline Cadillac Owners Member
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    Re: does ECU prevent engine braking

    BBOB this is the place How do I close the other posts. Im new to this and got lost. I returned the plunger and got 480 RPM then Pushing on the linkage didnt work at first but I remembered you said something about the TPS switch and I remembered seeing the E.8.5 must be same as E85 says me. I moved the tps untill I could feel the ISC moving while pushing on it Got the off on but had to let the throtle snap closed. I shortened the doubble return spring now --- off each time the throtle closes and idle at 730 in drive and when I let the throttle snap closed idle is 680 but the TPS WAS A GUESS it needs to be set correctly.

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    Re: does ECU prevent engine braking

    Sounds like the TPS is way out of whack....

    Probe the wires going into the TPS. With ISC motor fully retracted and the throttle at the closed bore position one of the TPS leads should read 5.0 volts and another around 0.5 volts with the key on. Adjust the TPS with the throttle in the min air position until you get 0.5 volts on that lead. Then the TPS will be close.

    It still sounds like the closed throttle switch is not making sometimes. Double check it's operation while driving using the onboard diagnostics. Just activate after you start the engine and you can drive while in diagnostics and watch the OFF icon for the closed throttle switch status.

    Go to the post, click on EDIT and delete the post so that it is blank or just put moved in the box.

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    Re: does ECU prevent engine braking

    Quote Originally Posted by bbob
    Not sure what you are talking about..... There is nothing like this that I know of. "overrunning clutches" are used in many different automatic transmsissions but not for the purpose of preventing engine braking. Besides, allowing engine braking actually saves fuel economy....eliminating engine braking would hurt fuel economy.

    Overrunning clutches in transmissions allow them to function by "adding" a clutch apply to effect a shift so that the previous gear lockup scheme can "overrun" when the next clutch applies. This way the timing of only one clutch is critical. Other automatics use a clutch-to-clutch scheme without overrunning clutches so that one clutch for the lower gear releases as the clutch for the next gear applies. The requires timing and syncronization of two clutches for a shift... Possibly this is what you heard about...???
    I guess it's best explained by a transmission professional.
    From "The Dictionary of Automotive Terms":

    overrunning clutch:
    [1] A clutch mechanism that will drive in one direction only. If driving torque is removed or reversed, the clutch slips.
    [2] A part of a starter motor designed to avoid armature damage caused by severe overrevving.
    [3] A device in an automatic transmission that disengages the engine on overrun
    See:
    freewheeling
    one-way clutch

  4. #19
    CAPTJACK is offline Cadillac Owners Member
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    Re: does ECU prevent engine braking

    bbob The tps closed angle is out of reach. However everything is great = Idle at 650 - 700 throtle closing at all speed except I have to tap the gas some times to get the off indidication. Even with all the linkage, TPS, & ISC removed the butterflys need a little help to fully close. There are marks on the throtle body in 4 places where the edge of the butterflys meet when fully closed I can find no other place that is causing any binding.

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    Re: does ECU prevent engine braking

    What do you mean the TPS closed angle is out of reach...???

    Retract the idle speed control motor fully, close the throttle to get the 450-500 idle as you describe and ADJUST THE TPS to get the .5 volts. Don't try closing the blades further. Loosen the screws holding the TPS and adjust it to .5 volts and then retighten the TPS and check the setting.

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    Re: does ECU prevent engine braking

    Quote Originally Posted by Katshot
    I guess it's best explained by a transmission professional.
    From "The Dictionary of Automotive Terms":

    overrunning clutch:
    [1] A clutch mechanism that will drive in one direction only. If driving torque is removed or reversed, the clutch slips.
    [2] A part of a starter motor designed to avoid armature damage caused by severe overrevving.
    [3] A device in an automatic transmission that disengages the engine on overrun
    See:
    freewheeling
    one-way clutch


    Sooo..... I explain to you what overrunning clutches are used for in an automatic transmission and you think I don't know what an overrunning clutch is...??? LOL LOL

    Sorry it wasn't clear to you. I meant that "I didn't know what you were talking about" in reference to an overrunning clutch allowing the transmission to coast or glide for fuel economy....

    While you are in the dictionary there, look up sprag clutch and one way roller clutch and sort out the difference and report back...LOL...hint: They are both overrunning clutches.

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    Re: does ECU prevent engine braking

    I like the name "Mechanical Diode" better.....

  8. #23
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    Re: does ECU prevent engine braking

    Quote Originally Posted by bbob
    Sooo..... I explain to you what overrunning clutches are used for in an automatic transmission and you think I don't know what an overrunning clutch is...??? LOL LOL

    Sorry it wasn't clear to you. I meant that "I didn't know what you were talking about" in reference to an overrunning clutch allowing the transmission to coast or glide for fuel economy....

    While you are in the dictionary there, look up sprag clutch and one way roller clutch and sort out the difference and report back...LOL...hint: They are both overrunning clutches.
    DUH! LOL..hint: I knew that.
    The point was that the overrun clutch could make the car "feel" like it's gliding to an extent since it severely limits the engine-braking affect. I was just mentioning that MAYBE this was contributing or responsible for what he was experiencing.
    Remember this?:
    My question is: Is it possible that this 89 FLEETWOOD of mine is designed to eliminate engin braking to save the power trainl
    I was only trying to point out that YES, most modern cars ARE designed to greatly limit engine braking and that the overrun clutch was a major contributor to that end. You obviously don't agree. Big surprise.
    Sorry if I intruded on YOUR thread.

  9. #24
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    Re: does ECU prevent engine braking

    FWIW, early cars such as the 1930 Dodge Brothers had a knob you could pull out of dashboard that allowed the engine to freewheel on the downgrades in the interest of reduced wear and increased economy by use of a one-way sprag clutch. One of the shortcomings of the later Borg-Warner manual overdrive transmissions that used to be very popular was that when in overdrive, when the foot was removed from the gas pedal, the engine went to idle and there was no engine braking because of the same sprag clutch feature. Upon coming to a down grade the driver was required to floor the footfeed until the transmission downshifted out of overdrive and pull out the overdrive control handle to lock the transmission in third gear. This would give you the required engine braking. Newer automatic transmissions are advertised as having an indirect overdrive gear with a numerical ratio lower than one like the Borg-Warner but they do not have the over running clutch.

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    Re: does ECU prevent engine braking

    One day while cruising the local junkyard I came across a Chevy that had an odd transmission; a heavy duty three-speed with overdrive. One thing led to another and this wound up in a Chevy 1/2 ton Aluminum Step-Van along with a 2-53 series Jimmy railroad refrigerator car diesel that a guy used for years to service a "contract" mail and newspaper delivery route.

  11. #26
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    Re: does ECU prevent engine braking

    Quote Originally Posted by dkozloski
    One day while cruising the local junkyard I came across a Chevy that had an odd transmission; a heavy duty three-speed with overdrive. One thing led to another and this wound up in a Chevy 1/2 ton Aluminum Step-Van along with a 2-53 series Jimmy railroad refrigerator car diesel that a guy used for years to service a "contract" mail and newspaper delivery route.
    You mean 3-speeds PLUS an overdrive, meaning 4-speeds? Or was 3rd an overdrive ratio? Could you tell from the pan, what series tranny it was?

  12. #27
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    Re: does ECU prevent engine braking

    It was a heavy duty three speed manual with a Borg-Warner overdrive tailshaft housing. The only way you can spot one is to measure the center to center distance between the main and countershafts. I don't recall the dimensions.

  13. #28
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    Re: does ECU prevent engine braking

    Quote Originally Posted by Katshot
    DUH! LOL..hint: I knew that.
    The point was that the overrun clutch could make the car "feel" like it's gliding to an extent since it severely limits the engine-braking affect. I was just mentioning that MAYBE this was contributing or responsible for what he was experiencing.
    Remember this?:
    My question is: Is it possible that this 89 FLEETWOOD of mine is designed to eliminate engin braking to save the power trainl
    I was only trying to point out that YES, most modern cars ARE designed to greatly limit engine braking and that the overrun clutch was a major contributor to that end. You obviously don't agree. Big surprise.
    Sorry if I intruded on YOUR thread.

    You don't get it do you...???

    The over running clutches in the automatic transmissions are NOT for preventing engine braking. Modern cars are NOT designed to greatly eliminate engine braking and the overrunning clutches in the transmissions are NOT a "major contributor" to that end. And an "overrunning clutch" that is employed in an automatic transmission would not "severely limit" engine braking it would TOTALLY ELIMINATE it if it were used like that. The over running or one way clutches don't drag or slip in one direction....they just turn completely loose.

    This is not my opinion but a statement of fact. I have the power flow diagrams for a 4T60/65E, a 4T80E and a 4L80E in front of me and there are no overrunning clutches active or preventing engine braking in the units when driving down the road or coasting to a stop. They just do not function that way. Just because there is an "overrunning clutch" in an automatic transmission and the definition in some manaul suits your fancy does NOT mean that the overrunnig clutch is in there for preventing engine braking. If you disagree, get out the service manuals or power flow diagrams for the transmissions and tell me which overruning clutch that is in the unit you think is responsible for this. I have gone back and looked and they do not do that.

    No, this is not my thread. I wasn't yours, either. You post erroneous information, I correct it so that others are not mislead. You are obviously not going to pay attention or understand it so I could care less...I just don't want others to be misinformed by your erroneous comments. I am not making this up to argue with you...you were fed some bad info. It doesn't work like you were told.


    BTW....there ARE some street motorcycles that have clutch setups in them to partially eliminate engine braking. They are set up with an overrunning (or more appropriately a one way clutch) on some of the clutch plates in the clutch pack so that the engine is only held back by a small portion of the clutch on overrun. This way, if there is a severe, sudden overrun, the partial clutch pack will slip and prevent rear wheel lockup. This is in the market today on some superbikes. It is NOT employed on any automatic transmissions in cars that I know of and certainly not in any GM automatic transmissions at all.

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    Re: does ECU prevent engine braking

    The first application of over running sprag clutches in automatic transmissions that I am aware of was on the stators in the multi stage torque convertors such as the old Buick Twin Turbine Dynaflow. These had nothing to do with the transmission free wheeling but improved the efficiency of the transmission from torque convertor stall to highway speeds.

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    Re: does ECU prevent engine braking

    Quote Originally Posted by dkozloski
    It was a heavy duty three speed manual with a Borg-Warner overdrive tailshaft housing. The only way you can spot one is to measure the center to center distance between the main and countershafts. I don't recall the dimensions.
    Sorry dude, my mind jumped to automatics right away. I got you now.

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