@50MPH & above; Doggy and slight vibration
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HT4100 4.1, 4.5, 4.9 Discussion, @50MPH & above; Doggy and slight vibration in Cadillac Engine Technical Discussion; Hello. On my '83 De-ville w/4.1 I've been told that its not tranny or electrical, it's fuel! ( There are ...
  1. #1
    miles37grand is offline Cadillac Owners Member
    Automobile(s): '83 Sedan de-ville
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    @50MPH & above; Doggy and slight vibration

    Hello. On my '83 De-ville w/4.1 I've been told that its not tranny or electrical, it's fuel! ( There are new tires and balanced.) My gas tank is new, I've replace the fuel pump w/new fuel strainer. I've replaced the inline fuel filter and some gas line. No improvement! My fuel pressure before was 9.5psi. I've gained a half of psi. I should have 12 to 14 or 15, right?? My problem is slilght vibration at hiway speed and doggy. All other areas are good. So, what do you think? Thanks.

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  3. #2
    GarysBlues is offline Cadillac Owners Member
    Automobile(s): 1994 4.9 Sedan DeVille
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    Re: @50MPH & above; Doggy and slight vibration

    It continues to break up above 50. Or just when it hits that speed? Does it level out again as speed increase's?

  4. #3
    daniel58 is offline Cadillac Owners Fanatic
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    Re: @50MPH & above; Doggy and slight vibration

    The FSM calls for 10.5 psi fuel pressure, so you are good on that. I had a 83 4100 in an Eldo it ran pretty good for a 4100 but I replaced the timing chain, plugs, wires, cap, rotor, EGR and lots of vacuum lines to get it that way. These are a bit of a slug even when running good.

  5. #4
    miles37grand is offline Cadillac Owners Member
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    Re: @50MPH & above; Doggy and slight vibration

    The car still vibrates at 55,60&65. Could my catalitic converter need replacing or eliminating? There is some rust in it.

  6. #5
    daniel58 is offline Cadillac Owners Fanatic
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    Re: @50MPH & above; Doggy and slight vibration

    I have had a clogged cat suggested to me for problems I am having with a 4.5 someone will surely correct me if I'm wrong, but my recent research shows that you can check for a clogged cat with a vacuum gauge. If vacuum drops off while revving the eng it is sign of a clogged cat or muffler. If you can unbolt it or possibly remove an O2 sensor and test drive it, that would tell you also. Could be... can be quite expensive and not fix the problem as I have learned the hard way.

  7. #6
    miles37grand is offline Cadillac Owners Member
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    Re: @50MPH & above; Doggy and slight vibration

    More info for ya; My vacuum is 22 inches at an idle. I thought that the vacuum is suppose to drop as increasing rpm. Thanks alot to this site elsewhere, I have read my computer codes. They are;(4 codes) #13 Oxygen Sensor not ready; #15 Open Coolant Temp. Sensor; #32 Open Map Sensor Signal; And #52 PCM Memory Reset. Okay, now what do they mean?

  8. #7
    carnut is online now Cadillac Owners Master
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    Re: @50MPH & above; Doggy and slight vibration

    It means to erase all of them and then recheck when either the "service soon or service now" lights come back on. They could all be history codes. When this vibration happens at 55, pull the shifter down into the next lower gear and remain at that speed. Does the vibration get better or worse? I'm thinking torque converter clutch, but need more imput. Normally a plugged cat will show on a vacuum gauge by going to zero when revved up. If it drops to say, 10 or 5 then its probably OK.

  9. #8
    miles37grand is offline Cadillac Owners Member
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    Re: @50MPH & above; Doggy and slight vibration

    Ol' Carnut, you may be on to something! In 'D' as it makes it's last up-shift, it starts to vibrate. When I down shift to '3' the vibration stops. But, but a tranny shop man test drove it and said, nope the tranny is good, and it's not electrical (missing), its fuel. Get your fuel system in order and test your fuel pressure. This engine is pickie about it fuel pressure. So I did, and no change.

  10. #9
    steelybill is offline Cadillac Owners Enthusiast
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    Re: @50MPH & above; Doggy and slight vibration

    This is a long shot but a cam lobe may be wearing down, like an intake lobe, making a cylinder run a bit lean.......

    How does it run when you stand on it through the gears, like up to say 50 MPH , before OD? Smooth?

  11. #10
    carnut is online now Cadillac Owners Master
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    Re: @50MPH & above; Doggy and slight vibration

    The new DEXTRON/MERCON type VI tranny fluid is synthetic developed to reduce TCC shudder more common in the Ford OD trans. Would not hurt to change over when a service is done on the trans. Even 4 or 5 qts can help. Another thing a TCC will show once locked up is a secondary ignition miss not felt in 2nd, 3rd or 4th until TCC locks. Look closely for carbon tracks on spark plug insulators, spark plug wires routed incorrectly and crossfiring. The service manual says plug wires close to the wiring going into the distributor base can cause an induction miss. Make sure all wires are in their proper clips and retainers.

  12. #11
    carnut is online now Cadillac Owners Master
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    Re: @50MPH & above; Doggy and slight vibration

    Another simple test is to get to 55 and when you feel the shudder, lightly rest your foot on the brake pedal. Engine tone should change and TCC will be unlocked and the shudder should go away. Now we know its not road speed specific so rule out tires, wheels, axles.

  13. #12
    miles37grand is offline Cadillac Owners Member
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    Re: @50MPH & above; Doggy and slight vibration

    This is gettin' pretty in-depth! I like it, I like it alot! A worn cam lobe, yah I hope its a long long shot. This car has almost 38,000 miles on it. But ya know, my compression is ( in order by # ) 180,180,180,160,185,185,185,&170. #4 increased to 175 with a shot of oil. And ya know, I've installed new plug wires, they go all over the place and its crowded. If I keep the tranny it third, it drives pretty smooth, but I loose about 25%mpg's. Thats according to the car computer. Thanks alot!!

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