94 Fleetwood Brougham
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5.0 and 5.7 Discussion, 94 Fleetwood Brougham in Cadillac Engine Technical Discussion; I need help with a engine problem. I have a 94 Fleetwood Brougham with the 5.7 LT1 engine. When starting ...
  1. #1
    drivin_in_style is offline Cadillac Owners Member
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    94 Fleetwood Brougham

    I need help with a engine problem. I have a 94 Fleetwood Brougham with the 5.7 LT1 engine. When starting cold it runs great. When it gets up to full temperature however (about 20-30 min drive time) it starts running like it's misfiring and I often can smell unburned gas.

    I have replaced the temperature sensor, the ICM, the distributor cap and rotor (OUCH $$) new plug wires, and the plugs are platnium about 6 months old. What puzzles me is that it runs perfect until it gets hot. I would welcome any tips that others may have run across... Thanks

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  3. #2
    carguy16's Avatar
    carguy16 is offline Cadillac Owners Enthusiast
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    Re: 94 Fleetwood Brougham

    Im not a mechanic, but o2 sensors, egr valves, these are the only other things to think of. Only other thing is the Opti. I really dont have the slightest clue.

    I drive a 94 Fleetwood Brougham as well.


    Quote Originally Posted by drivin_in_style
    I need help with a engine problem. I have a 94 Fleetwood Brougham with the 5.7 LT1 engine. When starting cold it runs great. When it gets up to full temperature however (about 20-30 min drive time) it starts running like it's misfiring and I often can smell unburned gas.

    I have replaced the temperature sensor, the ICM, the distributor cap and rotor (OUCH $$) new plug wires, and the plugs are platnium about 6 months old. What puzzles me is that it runs perfect until it gets hot. I would welcome any tips that others may have run across... Thanks

  4. #3
    drivin_in_style is offline Cadillac Owners Member
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    Re: 94 Fleetwood runs bad when hot

    Coil, wires, ICM, temperature sensor, distributor cap/rotor, thermostat - these are what I have replaced already.

    Car runs fine until the thermostat opens up. When it is up to full temp (about 45 min run time) it begins to run rough and backfire. It loses power and sometimes I can smell gas like it is loading up.

    Until the car gets up to temp, it runs like a new car. I can't seem to find what makes the difference. Any help from similar experiences would be appreciated.

  5. #4
    N0DIH's Avatar
    N0DIH is offline Cadillac Owners Master
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    Re: 94 Fleetwood Brougham

    Knowing that it runs ok in "open loop" and not "closed loop" narrows it somewhat.

    1. Are there any codes, with or without a check engine light?
    2. The O2 isn't used in open loop, but is in closed.
    3. The coolant temp sensor (was it disconnected and forgotten when the optispark was replaced, this will do as you describe)
    4. Throttle position sensor is open and closed loop sensor, likely it is not it
    5. EGR is a not a sensor, but a closed loop output of the ECM.
    6. Was the timing chain replaced? This is similar to a problem I had on my 455 Pontiac, I was 1 tooth advanced on the crank gear. It ran ok until warm and I tried to get on it. Unlikely, but possible.

    It does sound like the Opti is acting up, almost like it is out of time or something (rotor put on a tooth or 2 retarded or advanced?). Can you disconnect the coolant temp sensor (this will kick it into open loop) and see it runs ok? This will drop back to fixed timing and ignore O2 input.

    If that helps, I would then move on to O2 sensors. Disconnect 1 at a time, and see if it runs ok with a code and then start to run ok.

    Let us know! There is a ton of experience on this board!

  6. #5
    ocjmakaveli's Avatar
    ocjmakaveli is offline Cadillac Owners Enthusiast
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    Re: 94 Fleetwood Brougham

    I'd say depending on how many miles you have on the car that it could be an egr malfunction or o2 sensors just to start off.

  7. #6
    Mr Cowl Hood's Avatar
    Mr Cowl Hood is offline Cadillac Owners Member
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    Thumbs up Re: 94 Fleetwood Brougham

    Quote Originally Posted by N0DIH
    Knowing that it runs ok in "open loop" and not "closed loop" narrows it somewhat.

    1. Are there any codes, with or without a check engine light?
    2. The O2 isn't used in open loop, but is in closed.
    3. The coolant temp sensor (was it disconnected and forgotten when the optispark was replaced, this will do as you describe)
    4. Throttle position sensor is open and closed loop sensor, likely it is not it
    5. EGR is a not a sensor, but a closed loop output of the ECM.
    6. Was the timing chain replaced? This is similar to a problem I had on my 455 Pontiac, I was 1 tooth advanced on the crank gear. It ran ok until warm and I tried to get on it. Unlikely, but possible.

    It does sound like the Opti is acting up, almost like it is out of time or something (rotor put on a tooth or 2 retarded or advanced?). Can you disconnect the coolant temp sensor (this will kick it into open loop) and see it runs ok? This will drop back to fixed timing and ignore O2 input.

    If that helps, I would then move on to O2 sensors. Disconnect 1 at a time, and see if it runs ok with a code and then start to run ok.

    Let us know! There is a ton of experience on this board!


    I am with you on most of these points except for the Opti being installed incorrectly. When these are forced on the wrong way the car runs like crap no matter what loop it's in.

    Going to closed loop is in his fix, so I'd look at the coolant sensor, IAT, TPS and O2's on a good scan tool. Also, being OBD1, it may not set a code, but if there are any, that would be helpful as well. If the check engine light is on, it should not be if all is correct on the engine.

    Brian 96 Impala SS / 96 FWB

  8. #7
    N0DIH's Avatar
    N0DIH is offline Cadillac Owners Master
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    Re: 94 Fleetwood Brougham

    You can get a resistor and fix the CTS and IAT to fixed values and test with them. Might shed some light there. The CTS should read around ambient temp when the engine is cold. So before you start it, press off and warmer, and go to pointer 24, and hit outside temp. It should read around ambient temp in celcius.

    IAT and CTS can be read with a DVM. I will have to dig up the temp chart, anyone have it handy? Then you can come up with an approx resistor value if one sensor is off.

    CTS and IAT wil toss a code if open and run like crap, but if shorted, they toss a code and ignore and run decent.

    Was TPS disturbed? This will screw up a lot. But I would not expect it to be a problem in closed loop only, it will be all the time.

    Bad wires? Just because they are new doesn't mean they are always good, same goes with plugs. Fuel mixture is richer when cold (open loop) and can mask a weak ignition.

  9. #8
    drivin_in_style is offline Cadillac Owners Member
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    Re: 94 Fleetwood Brougham

    I just heard from the mechanic working on the Fleetwood. He ran a scan tool and tells me that the engine is operating normally at first. It gives a code 42 (which should only happen on cranking), but the code keeps recurring.

    He also asked me about the cam position sensors. Evidently this is only part of a complete distributor replacement, vs. the cap/rotor that I replaced. The whole distributor here in Canada is $700 cost! If anyone knows where I can get the cam position sensors separately, please let me know.

    Thanks for all your help guys.

  10. #9
    Mr Cowl Hood's Avatar
    Mr Cowl Hood is offline Cadillac Owners Member
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    Wink Re: 94 Fleetwood Brougham

    Quote Originally Posted by drivin_in_style
    I just heard from the mechanic working on the Fleetwood. He ran a scan tool and tells me that the engine is operating normally at first. It gives a code 42 (which should only happen on cranking), but the code keeps recurring.

    He also asked me about the cam position sensors. Evidently this is only part of a complete distributor replacement, vs. the cap/rotor that I replaced. The whole distributor here in Canada is $700 cost! If anyone knows where I can get the cam position sensors separately, please let me know.

    Thanks for all your help guys.

    Hmmm there seems to be a little confusion up there. The Optispark (distributor) has no cam position sensors as their traditionally known. The Optispark has a low and high resolution encoder built into it that reads the cam's position right into the PCM. These also determine timing coordination as well. There's no "extra" cam position sensor to consider so you should be okay there.

    There is a relatively new product that replaces the GM Optispark called the Dyna Spark. It is the same in theory, but has a billet aluminum housing and precision designed rotational system that is said to spin correctly and last a lot longer. They retail for $510 US. I haven't tried one yet but I hear great things about them -- spinning motors to 7200 rpm and with no faults!

    Anyway, since I am not familiar with Code 42, I can't help you there, but I'd have to guess that it's something ignition related and could be as little as your coil wire being loose.

    Brian 96 Impala SS / 96 FWB

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