92 Seville 4.9 runs fine until operating temp,
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Cadillac Seville / Cadillac Eldorado Forum Discussion, 92 Seville 4.9 runs fine until operating temp, in Past Cadillac Vehicle Discussion; I have a 92 Seville 4.9 litre engine. My problem is the car starts and runs great. After driving and ...
  1. #1
    lizzardman is offline Cadillac Owners Member
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    92 Seville 4.9 runs fine until operating temp,

    I have a 92 Seville 4.9 litre engine. My problem is the car starts and runs great. After driving and getting around 16 miles on the car and up to operating temp it starts running and bucking badly. After car cools for a few minutes it will run good again until it heats up again. The thermostat does work as I can see by the gauge going up and cooling back down. When it starts running badly It displays (Engine Hot, Idle Engine ,Turn A/C Off. I have pulled over and checked the coolant temp it was cool. I have replaced the 2 temp sensors and a MAT sensor. Also replaced the throttle position sensor and a bad alternator. Any Help would be greatly appreciated.
    Thanks in advance.

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  3. #2
    basscatt's Avatar
    basscatt is offline Cadillac Owners Master
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    Re: 92 Seville 4.9 runs fine until operating temp,

    Quote Originally Posted by lizzardman View Post
    I have a 92 Seville 4.9 litre engine. My problem is the car starts and runs great. After driving and getting around 16 miles on the car and up to operating temp it starts running and bucking badly. After car cools for a few minutes it will run good again until it heats up again. The thermostat does work as I can see by the gauge going up and cooling back down. When it starts running badly It displays (Engine Hot, Idle Engine ,Turn A/C Off. I have pulled over and checked the coolant temp it was cool. I have replaced the 2 temp sensors and a MAT sensor. Also replaced the throttle position sensor and a bad alternator. Any Help would be greatly appreciated.
    Thanks in advance.
    ---------------------------
    simply throwing parts at a problem - and HOPING something sticks -
    is a VERY expensive way to "fix" it - and RARELY WORKS -

    start by checking for Diagnostic Trouble Codes -

    if you don't know how - go here and read the ENTIRE post -

    http://www.cadillacforums.com/forums...odes-dtcs.html

    if you have any codes - post them here -
    ALONG WITH THEIR DEFINITIONS -
    your car is OBD1 codes -
    ----------------------------------

    The thermostat does work
    as I can see by the gauge
    going up and cooling back down

    I have pulled over and checked the coolant temp it was cool.


    well - which one is it?

    either the gauge works - and it is HOT -
    or you checked the coolant - and it was cool -

    can we assume you have checked for proper coolant level -
    and the pressure cap is good?

    the most common problem to overheating with a 4.9 motor -
    is a defective water pump -

  4. #3
    lizzardman is offline Cadillac Owners Member
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    Re: 92 Seville 4.9 runs fine until operating temp,

    There are no current codes stored. Last one current was TPS which was changed and adjusted to specs.The 3 sensors (new GM) I had from a previous 92 I sold before installing. The gauge and radiator coolant are within a few degrees of each other. Gauge misreads as soon as the car starts running bad. Will go from 183 degrees on 55mph road (have 180 therm) to 304 as soon as the car starts running bad. Measured with a quality infrared thermometer. Car otherwise heats up to 223 degrees fan kicks on cools down to 205 fan goes off like normal. My Coolant level is fine cap is holding 18 lbs. pressure. Water pump recently replaced and flow is good. But just to be sure I will check again.

  5. #4
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: 92 Seville 4.9 runs fine until operating temp,

    Definitely sounds sensor related, but 3 sensors would rule the sensor out. Can you tell what comes first, the poor performance or the high temp indication?

  6. #5
    lizzardman is offline Cadillac Owners Member
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    Re: 92 Seville 4.9 runs fine until operating temp,

    As far as I can tell the performance issue is noticed first but as soon as I look at the info center its reading Idle Engine, Engine Hot. When I shut the car off the fans will turn on and off continuously until the ignition is turned off. If I let the car sit about ten minutes it will start and run normally until it decides to act up again.

  7. #6
    Ranger's Avatar
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    Re: 92 Seville 4.9 runs fine until operating temp,

    Might check the ground. If not maybe a bad PCM, but that's just a guess.

  8. #7
    drewsdeville is offline Cadillac Owners Master
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    Re: 92 Seville 4.9 runs fine until operating temp,

    New or not, I would confirm a properly working sensor (concerned with the one at the t-stat housing) with the VOM. Check resistance as temp increases, and at the seemingly false 300 degrees.

  9. #8
    lizzardman is offline Cadillac Owners Member
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    Re: 92 Seville 4.9 runs fine until operating temp,

    Quote Originally Posted by Ranger View Post
    Might check the ground. If not maybe a bad PCM, but that's just a guess.
    Ranger I have checked all grounds associated with engine management and pulled apart and cleaned. The ground located on the front of the engine (left side) close to the coolant pipe was a bear to get to. I decided to cut the wire at the eyelet and run a new ground wire straight to the battery ground. The other grounds looked good. I have put it all back together and drove for an hour with the A/C on and off. No problems have surfaced since cleaning and running the ground wire. Car runs like it used to. Time will tell.
    I would like to thank everyone for their input.

  10. #9
    lizzardman is offline Cadillac Owners Member
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    Re: 92 Seville 4.9 runs fine until operating temp,

    Problem has persisted! After checking all sensors and grounding points I have just put a ECM (PCM) and I'm going to take for a test ride. More to follow after this test ride.

  11. #10
    lizzardman is offline Cadillac Owners Member
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    Re: 92 Seville 4.9 runs fine until operating temp,

    New PCM and still the same problem of all of a sudden runs bad and then cuts off. Have checked all the PCM grounds in the connectors to the PCM all were good. How warm should the PCM get when car is running.

  12. #11
    Ranger's Avatar
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    Re: 92 Seville 4.9 runs fine until operating temp,

    Not sure exactly how warm they get, but they get warm enough for GM to place the Northstar PCM in the intake air stream to help cool them.

  13. #12
    lizzardman is offline Cadillac Owners Member
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    Re: 92 Seville 4.9 runs fine until operating temp,

    I had taken the car for a 40 mile test ride today this morning and nothing happened. The car ran perfect. Ambient air temp was 81 degrees. I decided later in the afternoon to try the car again. Out side ambient temp is 94 degrees at the time of this test ride. Ten miles in and the problem starts, running bad telling me the engine is hot when its not checked with thermal temp gun. I shut off the car let it sit 5 minutes turn the key it runs fine. I start driving home and notice some of my gauges are not working properly like the mph. The speedometer says 0 mph while I'm traveling at 50. The car is running fine. I now notice as soon as the speedometer starts to work the car will start running bad. As soon as it stops registering my speed and reads 0 the car again runs fine. This is a digital dash. Could the dash be heating up from this Arizona sun and shorting out the display? Are these cars prone to digital dash problems?

    ----------

    I forgot there are no ECM Codes or other system codes.
    Thanks in advance for any help.

  14. #13
    lizzardman is offline Cadillac Owners Member
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    Re: 92 Seville 4.9 runs fine until operating temp,

    It was a bad pcm/ecm. the replacement computer was the wrong one. Had wrong service code printed on the unit. I had purchased a used one with the proper service code and have not had anymore problems.

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