1991 Fleetwood 4.9 high speed power loss
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HT4100 4.1, 4.5, 4.9 Discussion, 1991 Fleetwood 4.9 high speed power loss in Cadillac Engine Technical Discussion; HI all- Have a 1991 fleetwood (FWD). This car is losing power at high speed (passing, quick acceleration) once it ...
  1. #1
    Caddy-chris is offline Cadillac Owners Member
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    1991 Fleetwood 4.9 high speed power loss

    HI all-

    Have a 1991 fleetwood (FWD). This car is losing power at high speed (passing, quick acceleration) once it has warmed up. If you rev it up to higher RPMs at idle (in park) it acts like you are "pulsing" the gas pedal eg reving it up at fast intervals. One other thing to note is that the car will run great sometimes for an hour or so on the highway before the problem occurs and other times just for a few minutes. Once it starts acting up though, it gets worse and worse until you can barely accelerate from a standstill (a self propelled snow blower could kick me off the line slow!), however once you are moving, the car will maintain pretty much any speed you can manage to get it up to (downhills really help here).

    NO error codes past or present
    Exhaust is not restricted
    changed out coil, O2 sensor, MAP, MAT, Coolant temp, fuel presure reg.
    -However all the values were OK on these before I replaced them & still are withing range all having logical values depending on engine speed, temp etc.

    I have checked all the engine wiring to the dash harness with an ohm meter from every sensor, all of it checked out no problem.

    Fuel pressure is a steady 40 PSI until the problem starts and the it flutters at the 40 PSI mark - no change with disconnected fuel pressure regulator or when I swapped it out with one from a good runner.

    any suggestions you have would be very much welcomed at this point otherwise I can provide you with a map of where to find the car at the bottom of the lake!

    Thanks,

    Chris

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    Stoneage_Caddy's Avatar
    Stoneage_Caddy is offline Cadillac Owners 10000+ Posts
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    Re: 1991 Fleetwood 4.9 high speed power loss

    pressure sounds low to me... fuel filter or fuel pump ? vaccum leak @ or before regulator ?

  4. #3
    Caddy-chris is offline Cadillac Owners Member
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    Re: 1991 Fleetwood 4.9 high speed power loss

    Thanks stoneage,

    Replaced fuel filter this summer, I am thinking at this point that it is either fuel pump or bad injector. Forgot to mention that fuel used does NOT reflect what I am putting into the tank - at least 10-15 litres off! Check for vacuum leaks, replaced some suspect hoses, vacuum gauge reads normal. Also - reading on fuel pressure gauge does not change when the regulator is connected or dissconected. I think that 40 PSI is within spec though, if I remember correctly from the service manual. ( 37-42 sounds familiar)

    At least it still looks great in the driveway,

    Chris

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    Re: 1991 Fleetwood 4.9 high speed power loss

    Quote Originally Posted by Caddy-chris
    HI all-

    If you rev it up to higher RPMs at idle (in park) it acts like you are "pulsing" the gas pedal eg reving it up at fast intervals. One other thing to note is that the car will run great sometimes for an hour or so on the highway before the problem occurs and other times just for a few minutes. Once it starts acting up though, it gets worse and worse until you can barely accelerate from a standstill (a self propelled snow blower could kick me off the line slow!), however once you are moving, the car will maintain pretty much any speed you can manage to get it up to (downhills really help here).

    Fuel pressure is a steady 40 PSI until the problem starts and the it flutters at the 40 PSI mark - no change with disconnected fuel pressure regulator or when I swapped it out with one from a good runner.

    Thanks,

    Chris
    The pulsing in Park or Neutral when you try to rev it is a built in feature as near as I can tell. My '94 LeSabre and my wife's '99 Alero both do it it. Put in 1st and you can rev 'em out all you want.

    As for the other symptoms it sounds EXACTLY like what my LeSabre was doing just before the fuel pump went. Minimum PSI for mine was supposed to be 45 as I recall and it was putting out 38-40. Had it to the shop 3 times before it would do it for them.

  6. #5
    inmycadillac's Avatar
    inmycadillac is offline Cadillac Owners Enthusiast
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    Exclamation Re: 1991 Fleetwood 4.9 high speed power loss

    Quote Originally Posted by Caddy-chris
    HI all-

    Have a 1991 fleetwood (FWD). This car is losing power at high speed (passing, quick acceleration) once it has warmed up. If you rev it up to higher RPMs at idle (in park) it acts like you are "pulsing" the gas pedal eg reving it up at fast intervals. One other thing to note is that the car will run great sometimes for an hour or so on the highway before the problem occurs and other times just for a few minutes. Once it starts acting up though, it gets worse and worse until you can barely accelerate from a standstill (a self propelled snow blower could kick me off the line slow!), however once you are moving, the car will maintain pretty much any speed you can manage to get it up to (downhills really help here).

    NO error codes past or present
    Exhaust is not restricted
    changed out coil, O2 sensor, MAP, MAT, Coolant temp, fuel presure reg.
    -However all the values were OK on these before I replaced them & still are withing range all having logical values depending on engine speed, temp etc.

    I have checked all the engine wiring to the dash harness with an ohm meter from every sensor, all of it checked out no problem.

    Fuel pressure is a steady 40 PSI until the problem starts and the it flutters at the 40 PSI mark - no change with disconnected fuel pressure regulator or when I swapped it out with one from a good runner.

    any suggestions you have would be very much welcomed at this point otherwise I can provide you with a map of where to find the car at the bottom of the lake!

    Thanks,

    Chris
    Could be injectors but the first place to start is by cleaning throttle body. I have a 91 and had the same problem and after tb cleaning i was passing TA's again!

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