does ECU prevent engine braking
Cadillac
 

Cadillac Forums | Help Us Help You | Advertise | Cadillac Parts | Cadillac News | Cadillac Classifieds / (Old System)

Cadillac Technical Archive | Cadillac Dealers | Cadillac Reviews | Cadillac Dealer Reviews | Cadillac Vendors

CadillacForums.com is the premier Cadillac Forum on the internet. Registered Users do not see the above ads.
+ Reply to Thread
Page 1 of 3 1 2 3 LastLast
Results 1 to 15 of 33
HT4100 4.1, 4.5, 4.9 Discussion, does ECU prevent engine braking in Cadillac Engine Technical Discussion; I have been following the discussion on the HT4100 FOUM ie engin idle. I went through all the procedures suggusted ...
  1. #1
    CAPTJACK is offline Cadillac Owners Member
    Join Date
    May 2005
    Posts
    12

    Question engin braking

    I have been following the discussion on the HT4100 FOUM ie engin idle.
    I went through all the procedures suggusted because my concern was my brakes. It seemed that I had to over power the engine with brakes when slowing down or put it in nutruel.

    My question is: Is it possible that this 89 FLEETWOOD of mine is designed to eliminate engin braking to save the power trainl

  2. Remove Advertisements
    CadillacForums.com
    Advertisements
     

  3. #2
    CAPTJACK is offline Cadillac Owners Member
    Join Date
    May 2005
    Posts
    12

    does ECU prevent engine braking

    I have been following the discussion on the 85 - 92 HT4100 good stuff I went through all the suggustions and improved the idle problem. However my 89 Fleetwood will not slow down when I let off the throtle unless I put it in N I even disconnected the cruse control cable ..??? Is it posobile that this car is designed to eliminate Engine Braking to save Drive Train???

  4. #3
    DrDave is offline Cadillac Owners Fanatic
    Join Date
    Feb 2005
    Posts
    124

    Re: does ECU prevent engine braking

    I had that prob when my coil went out and was giving weird electrical problems.. prolly giving bad info to the computer...?

  5. #4
    90Brougham350's Avatar
    90Brougham350 is offline Cadillac Owners Connoisseur
    Automobile(s): 94 FWB, 93 SDV, 94 FWB (sold), 90 Brougham (sold)
    Join Date
    Jan 2005
    Location
    River Falls, WI
    Age
    28
    Posts
    3,730

    Re: engin braking

    So you had to give the engine a little gas to bring the rpm's up to give you more brake boost?

    Brian

  6. #5
    BeelzeBob's Avatar
    BeelzeBob is offline I'm a Cadillac Fanatic!
    Join Date
    Dec 2002
    Location
    Fort Lauderdale, Florida
    Age
    49
    Posts
    9,577

    Re: does ECU prevent engine braking

    No, the ECM allows engine braking. It sounds like the throttle is not returning to the correct coast down throttle angle when you lift off. Are you sure that the closed throttle switch is "making" and that the idle speed motor is retracting properly...???

    Do the full retract on the idle speed control motor and see where the engine idles when the throttle lever is at the closed bore position. It should idle down to about 450-500 and/or almost stall. If not, something is holding the throttle open.

  7. #6
    BluEyes's Avatar
    BluEyes is offline Cadillac Owners Enthusiast
    Automobile(s): 1970 Sedan deVille hardtop
    Join Date
    Feb 2005
    Posts
    595

    Re: engin braking

    It is possible. It seems that alot of newer AT's are designed to disengage or something when you take your foot off the gas. Probably for better fuel economy rather than powertrain savings.

    90Brougham - If I have everything correct, he is not referring to the vacuum assist on the brakes, but engine braking - like putting it in a lower gear in a stickshift to help slow down faster.

  8. #7
    Katshot's Avatar
    Katshot is offline Cadillac Owners Master
    Join Date
    Jan 2003
    Location
    Newtown, PA
    Age
    55
    Posts
    6,472

    Re: does ECU prevent engine braking

    I think he's probably refering to the over-run clutches in newer transmissions (at least I think that's what they call it). I don't think there's anything controlling this in the ECM/PCM, it's only in the trans itself as I recall.
    It's my understanding that this feature was added years ago in an effort to help fuel mileage.

  9. #8
    BeelzeBob's Avatar
    BeelzeBob is offline I'm a Cadillac Fanatic!
    Join Date
    Dec 2002
    Location
    Fort Lauderdale, Florida
    Age
    49
    Posts
    9,577

    Re: does ECU prevent engine braking

    Quote Originally Posted by Katshot
    I think he's probably refering to the over-run clutches in newer transmissions (at least I think that's what they call it). I don't think there's anything controlling this in the ECM/PCM, it's only in the trans itself as I recall.
    It's my understanding that this feature was added years ago in an effort to help fuel mileage.

    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...???

  10. #9
    illumina's Avatar
    illumina is offline Cadillac Owners Connoisseur
    Automobile(s): '98 Buick Regal LS - '91 Caddy Seville - '87 Caddy Seville!
    Join Date
    Feb 2004
    Location
    The Empire...
    Posts
    4,425

    Re: does ECU prevent engine braking

    You two (Bbob and Katshot) aren't going to start arguing over a damn ECM are you?

  11. #10
    Katshot's Avatar
    Katshot is offline Cadillac Owners Master
    Join Date
    Jan 2003
    Location
    Newtown, PA
    Age
    55
    Posts
    6,472

    Re: does ECU prevent engine braking

    Don't worry, the LAST thing I need is to do that. Especially on a subject that I admitedly have little expertice. My point was simply that overrun clutches allow the car to "glide" when you let up on the gas, while allowing the engine to return almost to an idle speed. At least that is how it was explained to me years ago, and maybe THAT was what the guy was experiencing. I can understand the reasons for them as explained by Bbob. Makes total sense. I have a hard time understanding this statement though:
    "allowing engine braking actually saves fuel economy....eliminating engine braking would hurt fuel economy."

  12. #11
    CAPTJACK is offline Cadillac Owners Member
    Join Date
    May 2005
    Posts
    12

    Re: does ECU prevent engine braking

    engin idle with adjust nut removed 480 engin idle with piston retracted 450 butterfly sticking in throttle body a little at this point not always fully closing and a little stubborn when opening. With adjustment screw in and adjusted at .030 air gap rpm at 490, these differances are proably because of different times and temps not any thing that was done. Plugged in rpm goes to 1030 in gear 830. On level road at 45 MPH let off gas = takes 1 mi to slow to 41 MPH RPM 1380 Put in N and RPM = 1480
    back in gear D brake to stop RPM 850

  13. #12
    CAPTJACK is offline Cadillac Owners Member
    Join Date
    May 2005
    Posts
    12

    Re: does ECU prevent engine braking

    bbob the ISM does not go all the way back when the engine is running at any time except when I open throtle and force it back , Gently of course with my gold plated adjustment screwdriver, it stayes there at 450 - 500 rpm then climbs to 680 and stays untill throtle is hit and then only comes back to 850 to 1030 depending what is on ie AC lights etc.

  14. #13
    BeelzeBob's Avatar
    BeelzeBob is offline I'm a Cadillac Fanatic!
    Join Date
    Dec 2002
    Location
    Fort Lauderdale, Florida
    Age
    49
    Posts
    9,577

    Re: does ECU prevent engine braking

    Quote Originally Posted by Katshot
    Don't worry, the LAST thing I need is to do that. Especially on a subject that I admitedly have little expertice. My point was simply that overrun clutches allow the car to "glide" when you let up on the gas, while allowing the engine to return almost to an idle speed. At least that is how it was explained to me years ago, and maybe THAT was what the guy was experiencing. I can understand the reasons for them as explained by Bbob. Makes total sense. I have a hard time understanding this statement though:
    "allowing engine braking actually saves fuel economy....eliminating engine braking would hurt fuel economy."

    Over running clutches are not put into automatic transmissions to allow them to "glide" . If you notice, the engine doesn't return to a normal idle speed when you let off the throttle...the transmission pushes the engine causing overrun braking.



    When an engine is in an overrun condition the fuel delivered is very low. In many cases the injectors turn completely off on decels and the engine is kept turning by the transmission. This is done primarily to prevent unburned hydrocarbons from causing the catalytic converter from overheating but it also takes precious little fuel (especially when the injectors are turned completely off...) to keep the engine running while the car is continuing down the hill or coasting along. If the engine were to simply be allowed to return to idle it would take more fuel to idle the engine than it would take if it were being driven by the transmission in heavy overrun. So, for short intervals, heavy engine overrun, especially leading to fuel shutoff, can improve fuel economy as apposed to simply letting it "glide" and idle on it's own taking fuel to over come the friction of idling on it's own.

  15. #14
    BeelzeBob's Avatar
    BeelzeBob is offline I'm a Cadillac Fanatic!
    Join Date
    Dec 2002
    Location
    Fort Lauderdale, Florida
    Age
    49
    Posts
    9,577

    Re: does ECU prevent engine braking

    Quote Originally Posted by CAPTJACK
    bbob the ISM does not go all the way back when the engine is running at any time except when I open throtle and force it back , Gently of course with my gold plated adjustment screwdriver, it stayes there at 450 - 500 rpm then climbs to 680 and stays untill throtle is hit and then only comes back to 850 to 1030 depending what is on ie AC lights etc.

    Is the closed throttle switch working...???

    Enter into diagnotics with the engine idling and in drive by pressing the OFF and WARMER as normal. After any codes display the display will show .7.0 as a prompt. Watch the icons on the climate control panel. The OFF icon indicates the status of the closed throttle switch. When the OFF icon is lit the closed throttle switch is closed...i.e..the throttle lever is resting on the idle speed control motor plunger. When the OFF icon is off then the closed throttle switch is open indicating that the throttle is opened. Watch the closed throttle switch status when you drive and when the idle speed control is acting up. If your foot is off the accelerator then the OFF icon should be lit....if not then something is holding the throttle open or the closed throttle swtich inside the idle speed control motor is failing. If the throttle is closed and resting on the idle speed control motor plunger and the OFF icon is not indicating that the closed throttle switch is closed then something is wrong with the closed throttle switch. Easy fix here is to replace the idle speed control motor.

    Something may be restricting the throttle lever or the throttle linkage so that the throttle return spring is not strong enough, on it's own, to hold the throttle against the idle speed control motor plunger hard enough to close the switch inside. Try adding an additional throttle return spring temporarily as a test to see if that corrects the problem. If so, then find out where the binding is.

    It is easier to respond to one post like this. Multiple posts on the same topic in other areas just cause more confusion. Indicate which post are you going to follow and I will repsond at that one.

  16. #15
    Conductor Al is offline Cadillac Owners Member
    Join Date
    May 2005
    Posts
    6

    Re: engin braking

    It depends. I had an 89 Fleetwood Brougham and engine braking rarely did any good on my regular commutes. On moderate hills it would slow the car but on the mountain that we lived on, it wouldn't even hold the speed due to the combination of the vehicle weight and the grade of the road which was more than 7% for about 6 miles. Set it in 3rd and it was like driving in regular Drive-no effect at all. 2nd wasn't much better but 1st would drag the car down to 25. Whether or not you'd still be in the car depended on whether your seatbelt was on. Also, that presented cars following an opportunity to rear end you, assuming you didn't trash the transmission. Due to the weather and amount of mountain driving, the car usually used up two sets of brake pads annually-unsafe to use lower gear in wet weather.

Quick Reply Quick Reply

Register Now

Please enter the name by which you would like to log-in and be known on this site.
If you do not want to register, fill this field only and the name will be used as user name for your post.

Please enter a password for your user account. Note that passwords are case-sensitive.

Please enter a valid email address for yourself.

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Bookmarks

Cadillac Posting Rules

  • You may post new threads
  • You may post replies
  • You may not post attachments
  • You may not edit your posts
Read about Lincoln | Buick | Kia Forte Forum
Need products for your Cadillac? Check out your options at the links below:

custom floor mats | Cadillac Chrome and Black Chrome Wheels | window tinting