Low speed hesitation on pull away.
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HT4100 4.1, 4.5, 4.9 Discussion, Low speed hesitation on pull away. in Cadillac Engine Technical Discussion; Hello to all you experts. I'm a brand new Cadillac owner so I need some expert advice. Just purchased a ...
  1. #1
    frankh is offline Cadillac Owners Member
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    Question Low speed hesitation on pull away.

    Hello to all you experts. I'm a brand new Cadillac owner so I need some expert advice. Just purchased a '95 DeVille, with 4.9 Engine a few weeks ago. About 81kMiles. Clean car, well maintained and not known to have been abused by prior owner. From day 1, I noticed that when I start off from a traffic light (i.e., from a dead stop) and try to go for a slow, smooth, easy build up of city street speeds, there is a momentary "dip" or hesitation, then the engine sort of catches up with itself and speed increases. By the sound of it, engine RPM does not actually slow down, rather, it takes a bit to react to gas pedal position. It almost feels like the result of a small vacuum leak in a regular carbourated engine, but this engine is throttle body fuel injected not normally carbourated. The car has plenty of pep and can do a jack rabbit start if I press down briskly on the gas pedal, and drives smoothly otherwise at all speeds. Any thoughts please? BTW, an acquaintance of mine said he has driven Cadillacs all his life and they are "just that way."
    Thanks for any response.

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    elwesso's Avatar
    elwesso is offline Cadillac Owners Master
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    Re: Low speed hesitation on pull away.

    Has the air filter been checked?? It could also be a clogged injector, dirty TB, fuel filter, etc......

    But, they will be that way, to a certain degree....... A big heavy car like this isnt going to have the throttle response of a little sport compact or whatever......

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    Katshot's Avatar
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    Re: Low speed hesitation on pull away.

    That is NOT the way they're supposed to be. You do have a problem causing it. There are MANY things that can cause your issue so it may take some looking. Mainly, it will take a good patient mechanic. A thorough tune-up and general inspection should reveal the problem. And yes, it could even be an intake leak.

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    frankh is offline Cadillac Owners Member
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    Re: Low speed hesitation on pull away.

    Quote Originally Posted by elwesso
    Has the air filter been checked?? It could also be a clogged injector, dirty TB, fuel filter, etc......

    But, they will be that way, to a certain degree....... A big heavy car like this isnt going to have the throttle response of a little sport compact or whatever......
    Air filter is not new but pretty clean (will change it nevertheless). Have good acceleration and smooth highway speed changes so I don't think it looks like a clogged fuel filter. A mechanic used one of those "injector cleaner" liquid kits, some right in the throttle body and some in the tank. Seemed to help just a bit for a short while (maybe just wishful thinking). Any thoughts about using that kind of stuff? Any particular kind ?

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    frankh is offline Cadillac Owners Member
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    Re: Low speed hesitation on pull away.

    Quote Originally Posted by Katshot
    That is NOT the way they're supposed to be. You do have a problem causing it. There are MANY things that can cause your issue so it may take some looking. Mainly, it will take a good patient mechanic. A thorough tune-up and general inspection should reveal the problem. And yes, it could even be an intake leak.

    When mechanic looked at it (see my reply to "Elweso") he said that there were no codes indicating any problems and even said the plugs didn't have to be changed. (He is a rare breed - not recommending work that he feels doesn't have to be done.) I am more inclined to believe it is a vacuum (intake) leak although I might put another can of "injector cleaner" through the system. My experience (years ago on my old Chrisler Imperial 440 Cu in) leads me to think that with the high underhood temps, especially here in Florida, those rubber/neoprene hose ends can get hard and brittle over metal fittings and loose some vacuum over time. Would you agree that would be a good place to start? What should a normal idle vacuum reading be, 29" to 30" ? (I don't have any shop manuals on the car or the engine).

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    Re: Low speed hesitation on pull away.

    Dudes hes having the same problem I am! Low idle hesitation! Same motor too!

  8. #7
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    Stoneage_Caddy is offline Cadillac Owners 10000+ Posts
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    Re: Low speed hesitation on pull away.

    " those rubber/neoprene hose ends can get hard and brittle over metal fittings and loose some vacuum over time."

    i dont have the problem myself , but i did notice that the vaccum line from the thottle plates thats about 4 inches long has been replaced on mine ....

    i will see if i have a vaccum gauge out in the garage and take a reading of my vaccum and post it in this thread

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    frankh is offline Cadillac Owners Member
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    Smile Re: Low speed hesitation on pull away.

    i dont have the problem myself , but i did notice that the vaccum line from the thottle plates thats about 4 inches long has been replaced on mine ....

    i will see if i have a vaccum gauge out in the garage and take a reading of my vaccum and post it in this thread[/QUOTE]

    Thanks for the tip. I'll look for that line first and see what condition its in. Please post your vacuum reading (and where you tapped in to a vacuum source) so I have something to go by. BTW, something that makes me feel even more that its a vacuum leak is that at a cold engine start-up, for a few short minutes (until the engine reaches normal operating temp) the hesitation is not bad at all. I would think that the slightly higher rpm and/or richer mixture at cold idle tends to compensate for a small vacuum leak. Once warmed up though, the hesitation is back.

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    Cruzship is offline Cadillac Owners Member
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    Exclamation Clean the EGR tubes

    I had exactly the same symptoms and found a thread at caddyinfo.com (http://caddymb.netgetgoing.com/ use the searchable archives)on cleaning the EGR tubes and throttle body, and it was right on.Not only ran like new, but added gas mileage back to what it got years ago!

  11. #10
    frankh is offline Cadillac Owners Member
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    Re: Clean the EGR tubes

    Quote Originally Posted by Cruzship
    I had exactly the same symptoms and found a thread at caddyinfo.com (http://caddymb.netgetgoing.com/ use the searchable archives)on cleaning the EGR tubes and throttle body, and it was right on.Not only ran like new, but added gas mileage back to what it got years ago!

    Thatr sounds like a winner! As soon as I can get the car back from my wife, I'll give it a try. But,....this may take a few days before I have access (she just loves the car).

    Frank

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    elwesso's Avatar
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    Re: Clean the EGR tubes

    Quote Originally Posted by Cruzship
    I had exactly the same symptoms and found a thread at caddyinfo.com (http://caddymb.netgetgoing.com/ use the searchable archives)on cleaning the EGR tubes and throttle body, and it was right on.Not only ran like new, but added gas mileage back to what it got years ago!
    Take off the TB, and reach inside the hole that the TB hooks to (plenum), and get some rags and TB cleaner....... It will make a world of difference!!!

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    frankh is offline Cadillac Owners Member
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    Smile Re: Clean the EGR tubes

    Quote Originally Posted by elwesso
    Take off the TB, and reach inside the hole that the TB hooks to (plenum), and get some rags and TB cleaner....... It will make a world of difference!!!

    That sounds like more than an hour's work, which is ok by me but not necessarily ok by the lady of the house. Its almost impossible to get posession long enough to for the engine to cool down so I can work on it. Will try the vacuum lines and egr valve options first, then the TB removal etc., if needed. Thanks for the tip.

    Frank H

  14. #13
    elwesso's Avatar
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    Re: Clean the EGR tubes

    TB removal isnt really that hard...... Maybe 20 mins to get it off, and then however long it take you to clean/replace......

    Might as well do it all and not have to worry about it!!!

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    frankh is offline Cadillac Owners Member
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    Thumbs up Re: Clean the EGR tubes

    Quote Originally Posted by elwesso
    TB removal isnt really that hard...... Maybe 20 mins to get it off, and then however long it take you to clean/replace......

    Might as well do it all and not have to worry about it!!!

    The only issue is getting the car alone to myself long enough. You know who, has claimed the car for herself. I'll have to wait a bit 'til she goes away for a weekend to visit the grandkids then I'l be able to muck around under the hood to my hearts content without getting "The Look".

    Thanks

  16. #15
    elwesso's Avatar
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    Re: Clean the EGR tubes

    If you take off that TB, I promise you the car wont be going anywhere!!!

    That could also cause other, non-TB related strife.....

    Just make sure you clean out that plenum as best you can before you put the TB back on...... You may have to rig up a rag on a dowel of some sort, but it will be worth it...... it will make a difference of night and day!!!!

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