Prom needed/High speed great, mid to idle speeds terrible. - Page 3
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RWD 19xx-1984 DeVille and Fleetwood,
1985-1996 Fleetwood and Brougham Forum Discussion, Prom needed/High speed great, mid to idle speeds terrible. in Past Cadillac Vehicle Discussion; Carnut, did exactly as you said and codes did vanish. Now have no codes , but trouble still there. Have ...
  1. #31
    gsim is offline Cadillac Owners Member
    Automobile(s): 1984 SEDAN DEVILLE
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    Re: Prom needed/High speed great, mid to idle speeds terrible.

    Carnut,
    did exactly as you said and codes did vanish. Now have no codes, but trouble still there. Have a steady 5# - 6# fuel pressure, no variation, but READ WITH AN AIR COND MANIFOLD GAUGE THO. Have steady 2 VDC on both injectors while running, no variation when engine stumbles. Did take reading on resistance of TPS. Goes smoothly from 2 1/2 ohms to 5 ohms and no jittering. Figure that part is ok too.

    So the only thing that I can point to so far is that I had a bad MAT sensor, and I still have low fuel pressure that is steady @ 5 or 6#. However, it runs just fine @ 70 MPH and above, so I am doubting a fuel pump issue. Am admitting to being stumped for now.

  2. #32
    jayoldschool's Avatar
    jayoldschool is offline GM RWD V8 addict
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    Re: Prom needed/High speed great, mid to idle speeds terrible.

    Why are you doubting fuel pump? You have low pressure. The car doesn't need much gas to cruise, it needs lots on acceleration. Look at the symptoms, the solution is staring you in the face.

  3. #33
    gsim is offline Cadillac Owners Member
    Automobile(s): 1984 SEDAN DEVILLE
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    Re: Prom needed/High speed great, mid to idle speeds terrible.

    Thank you, carnut. I did not know that. I figured that it would give trouble at all speeds if it was the pump. Remember now, it does stumble down and try to die when it is only sitting and idling. And I did read it with an Air Cond gauge, not a gauge made for reading fuel pressure. I did not want to jump to a conclusion, and especially one that involved pulling the fuel tank. LOL

    Gerry

  4. #34
    gsim is offline Cadillac Owners Member
    Automobile(s): 1984 SEDAN DEVILLE
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    Re: Prom needed/High speed great, mid to idle speeds terrible.

    Thank you, carnut. I did not know that. I figured that it would give trouble at all speeds if it was the pump. Remember now, it does stumble down and try to die when it is only sitting and idling. And I did read it with an Air Cond gauge, not a gauge made for reading fuel pressure. I did not want to jump to a conclusion, and especially one that involved pulling the fuel tank. LOL

    Gerry

  5. #35
    gsim is offline Cadillac Owners Member
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    Re: Prom needed/High speed great, mid to idle speeds terrible.

    Thanks, Jayoldschool. Will consider. I did not use the proper gauge and it does die when only idling too. Did not want to pull tank and all of that for nothing. Wanted to weigh in with this thing so to speak, and get opinions about it. Another thing is that it runs great at 70 and up and begins to act up at 60 and below. 60 to 30 at least are aldo cruising speeds so it does not cruise well at all except high speeds.

    Gerry

  6. #36
    jayoldschool's Avatar
    jayoldschool is offline GM RWD V8 addict
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    Re: Prom needed/High speed great, mid to idle speeds terrible.

    What happens when you are rolling at 70 and you put your foot to the floor?

  7. #37
    gsim is offline Cadillac Owners Member
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    Re: Prom needed/High speed great, mid to idle speeds terrible.

    Hey, Jayoldschool,
    If doing 70 and I stomp it, it will downshift for a bit and pick up speed. have run it to 85 with no trouble at all. It does not hesitate/stumble one bit but remains smooth. 65 and below it stumbles as it runs along. 30-40 it seems worse and it will not idle but must be kept running via gas pedal when stopped. Oh, I do recall that I did have the tank off once to re-install the connecting hose, pump-line. No clamps, and not possible to install them. And I knocked it loose last year trying to siphon some fuel for the mower. LOL. I thought it remarkably easy to slip back on and wondered if it should be tighter. Seemed to be a thickish hose, 7" - 8" long, nearly like foam rubber. I should call Cadillac and see if maybe that part is still available before I remove the tank. Maybe if I do all that work I should not put the old pump back either, but put in a new one from NAPA. The car is worth the risk to me so if no other leads present themselves to follow, I will likely try it.

    (the 4100 engine is too small for the weight of the DeVille IMO, and from what I have seen both on the highways here and in junkyards here, it was not too popular. Am guessing for that very reason? It tends to downshift more in mountainous terrain if I am trying to maintain 70 or so and that has always been the case.)

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