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RWD 19xx-1984 DeVille and Fleetwood,
1985-1996 Fleetwood and Brougham Forum Discussion, Problem at highway speeds in Past Cadillac Vehicle Discussion; Thanks, I think I may tackle it this weekend. This site is awesome I would have never figured this out....
  1. #16
    fireman130's Avatar
    fireman130 is offline Cadillac Owners Member
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    Thanks, I think I may tackle it this weekend. This site is awesome I would have never figured this out.

  2. #17
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    jayoldschool is online now GM RWD V8 addict
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    Re: Problem at highway speeds

    Fuses first!

  3. #18
    sven914 is offline Cadillac Owners Connoisseur
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    Re: Problem at highway speeds

    I was wrong about the MAF sensor, however the LO5 does have a Manifold Absolute Pressure (MAP) sensor, which serves the same basic function as a MAF; both sensors are used by the vehicle's computer to measure incoming air and determine the correct air/fuel ratio. A malfunctioning MAP would present the same symptoms as a malfunctioning MAF.

    I have driven more than one vehicle with a disconnected Torque Convert Clutch solenoid, and the TCC solenoid in my own car used to get stuck in the engaged position. Neither case presented anywhere near to the same drivability concerns as stated in the first post. I'm not saying that it's impossible for the TCC solenoid to be causing the issue, I'm just saying that it is highly unlikely.

  4. #19
    fireman130's Avatar
    fireman130 is offline Cadillac Owners Member
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    Can I try unplugging the solenoid to see if that helps? I also replaced the MAP sensor in my long list of parts we were throwing at the car. Thanks for the help

  5. #20
    cadillac_al is online now Cadillac Owners Connoisseur
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    Re: Problem at highway speeds

    I'm with Sven. I can't see this as a TC lockup issue but the fix looks pretty cheap and easy and the OP doesn't know if the trans was ever serviced. It would be a good time to service the trans before something bad happens to it anyway. Change the cheap solenoid and hope for the best. In my experience a bad MAP acts blubbery like the choke is on. A lot of cars run fine until they get locked up in OD. When they buck in OD it is usually ignition misfires or EGR. Then we would ask if you used quality plugs and wires or the cheap stuff and used factory plug gaps. Keep us posted.

  6. #21
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    fireman130 is offline Cadillac Owners Member
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    What has me thinking the TCC, is when I put my foot on the brake just a little to unlock the torque converter it works perfect.?????????...... I did replace the MAP sensor with no luck. The car still gives a lean 44 code though.

  7. #22
    drmenard is offline Cadillac Owners Enthusiast
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    Re: Problem at highway speeds

    I think it is not the transmission... I think it is a weak coil... I would change the coil and see if it makes a change...

  8. #23
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    Re: Problem at highway speeds

    I did change the coil with no help. I am going to try plugs and wires they look OK but I have no idea how old they are.

  9. #24
    carnut is offline Cadillac Owners Master
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    Re: Problem at highway speeds

    I think the lean code is your biggest clue. Once TCC engages and the car is running too lean, it will buck. Have you confirmed fuel pressure at that speed? I think you have a weak fuel pump or the screen (filter, sock) on the float sender.

  10. #25
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    fireman130 is offline Cadillac Owners Member
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    I just took the car up on the interstate and ran the wheels off of it. Around 55 it bucks and carries on, get past that and it ran perfect. I ran about 50 miles with the cruise set at 75 with no problems, get between 50-55 it bucks and surges. If I floor it, it takes off like a rocket.

    ----------

    This trip I did not get the lean code 44.

  11. #26
    csbuckn is online now Cadillac Owners Connoisseur
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    Well that won't be able to tell us any more info then we have already. The two main focuses are ignition strain or tc lockup. Unfortunately, both will give the same symptoms at cruising speeds at the lowest rpm and highest gear. Maybe take it to a tranny shop and see if they know how to test it? My money is still on tc solenoid.

  12. #27
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    fireman130 is offline Cadillac Owners Member
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    After all that fuss, we ruled out fuel pump, transmission, and spark. It ended up being the fuel pressure regulator on top of the throttle body. It's finally running like a Cadillac again!!!!!!! Thank you everybody for your help.
    csbuckn and talismandave like this.

  13. #28
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    jayoldschool is online now GM RWD V8 addict
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    Re: Problem at highway speeds

    Great news, and thank you for updating!

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