'92 Seville 4.9 questions
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HT4100 4.1, 4.5, 4.9 Discussion, '92 Seville 4.9 questions in Cadillac Engine Technical Discussion; I want to start out by saying thanks for everyone's posts and insights - it is amazing how much can ...
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    dac675's Avatar
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    Question '92 Seville 4.9 questions

    I want to start out by saying thanks for everyone's posts and insights - it is amazing how much can be learned on these forums. Personally, I am very famiiar with most of Ford and Chevy's engine systems, but I am somewhat new to the Caddy systems.

    Now to my first question: I have a '92 Seville with the 4.9. Lately, it seems that when I am braking for a stop, I am constantly fighting the engine. The tach shows it staying up at about 1250 rpm until the wheels come to a dead stop, and then it idles down. Needless to say, I fear what this may being to my brakes and my transmission, let alone my gas mileage. This problem has been going on for a couple of weeks and so far I have tried a couple of fixes. I know I was having issues with the switch in my idle speed control not consistantly responding when the throttle was resting on it so I changed the idle speed control. Also, in accordance with the advice elsewhere on these posts, I cleaned the throttle body, including the back of the butterfly plates and the EGR tubes underneath. I have reset the computer and let it relearn the idle values. Still it does the same thing. If I put it into diagnostics mode, it appears that the TPS is sendng an accurate signal, so I am at a loss for what to look for now. Anyone have any experience with this type of problem.

    A second question I have is this - when the ignition is on, I can always hear a relay clicking in the trunk. It keeps going regarless of whether the car is running or not. It sounds almost like it is clicking a trouble code. It does short, repeating sets of clicks and pauses. Are any of the relays supposed to be doing anything like this? Is this some sort of normal failure mode?

    Thanks for any help.

    dac675

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    bigmike2861 is offline Cadillac Owners Member
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    Re: '92 Seville 4.9 questions

    As for your first problem with fighting the engine. Its the TPS or throttle position sensor. It either needs replacing or to be reset. They run around 50 dollars so that should fix it.

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    BeelzeBob's Avatar
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    Re: '92 Seville 4.9 questions

    Before jumping to the conclusion that it is the TPS I would double check that the closed throttle switch is working correctly. What you are describing is classic symptoms of the closed throttle switch not "making" when the throttle is closed so the idle speed control does not know that you have released the throttle....so it holds the throttle open and fixed at the point the plunger extended to in anticipation of you closing the throttle. After you come to a stop the zero MPH flag sets and overrides the throttle switch requirement and goes to RPM control so the idle comes down to normal.


    Use the onboard diagnostics to verify the closed throttle switch activity. Enter into the onboard diagnostics and when the system prompts you with the ECM? prompt answer "yes" with the HI button. At this point the icons on the climate control panel take on new functions and indicate the status of various ECM parameters. The LO icon will indicate the status of the closed throttle switch. The LO icon will be on when the throttle switch is closed...i.e..when the throttle is resting on the ISC motor plunger. It will go out when you open the throttle. The icon should light up when you let off the throttle...at any time or speed. I am guessing that you are not going to see the closed throttle switch "make" when you are letting off.


    You might check that the throttle return spring is correct and has adequate tension to close the closed throttle switch. Also, check the throttle linkage and cruise control linkage to make sure that it is not restricting the throttle motion and preventing it from closing correctly.

    With the engine idling, open the throttle lever slightly to raise the RPM and simultaneously depress the ISC motor plunger. The ISC motor plunger should retract when you do this. Retract it completely and freeze the plunger retracted by disconnecting the wire connector to the ISC motor. Allow the throttle to close gently. The throttle should go to closed bore position, the engine should idle down to 450-500 (AC off) and there should be clearance between the ISC motor plunger and the throttle lever in this position. If there is no clearance then the plunger needs to be adjusted. There MUST be clearance between the plunger and the throttle lever at the closed bore position or the idle speed control soft ware in the ECM cannot properly learn the TPS setting and it will cause all sorts of problems. If there is no clearance and the ISC motor fully retracted with no problems then adjust the plunger of the ISC motor by turning it until there is about .030 clearance between the plunger tip and the throttle lever.

    Double check the closed throttle switch operation and the ISC plunger clearance at full retract and post back.

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    Re: '92 Seville 4.9 questions

    As far as the clicking in the trunk....climb in there and see what is clicking where and find out what it is.....

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    Re: '92 Seville 4.9 questions

    That relay in the back might be your power antenna not fully opening or closing, or the auto-leveling relay (I think thats in the back on a Seville)

    Bbob, I did the TPS adjustment on my 93 deville (ISC retracted & unplugged and ODB p01 - TPS (-.05 to .05) mine was -.18 !.
    Now at idle (ISC plugged in & 600RPM) the TPS reads 2.1 - 2.5, is that normal ?


    Use the onboard diagnostics to verify the closed throttle switch activity. Enter into the onboard diagnostics and when the system prompts you with the ECM? prompt answer "yes" with the HI button. At this point the icons on the climate control panel take on new functions and indicate the status of various ECM parameters. The LO icon will indicate the status of the closed throttle switch. The LO icon will be on when the throttle switch is closed...i.e..when the throttle is resting on the ISC motor plunger. It will go out when you open the throttle. The icon should light up when you let off the throttle...at any time or speed. I am guessing that you are not going to see the closed throttle switch "make" when you are letting off.
    What are the other lights for ?? I haven't found my service manual on ebay yet.

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    Re: '92 Seville 4.9 questions

    Quote Originally Posted by up2ng
    Bbob, I did the TPS adjustment on my 93 deville (ISC retracted & unplugged and ODB p01 - TPS (-.05 to .05) mine was -.18 !.
    Now at idle (ISC plugged in & 600RPM) the TPS reads 2.1 - 2.5, is that normal ?




    What are the other lights for ?? I haven't found my service manual on ebay yet.
    Sounds perfectly normal. Realize that the idle at the closed bore setting is supposed to be about 450 RPM...so that is just the reference point for the TPS learning to start. The control system uses that point as a reference and then calculates the TPS reading as an offset to that reference value. It is just an arbitrary point picked by the calibrators so don't make too much of it. The system would work with any sort of reference setting if it was set up that way in the beginning. In your case, by the time the throttle is opened by the ISC motor sufficiently to get to the 600 RPM idle the throttle is open 2.1-2.5 degrees. This isn't an absolute number for degrees....just the arbitrary reference values used... Remember that the ECM is constantly monitoring the RPM that the engine is at, looking at impending loads, ambient temperature, AC status, PS status, etc... and sending control inputs to the idle speed control motor to move the plunger in or out to effect the correct idle speed...or compensate for a sudden load by the AC compressor, etc...

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    Re: '92 Seville 4.9 questions

    Thanks for the guidance bbob. When I go into diagnostics mode, I am seeing the Lo indicator light up when the throttle comes to rest on the plunger. Even while driving. Also, if I raise the engine speed while holding down the switch, it does retact the plunger fully (and yes, there is at least 0.030 clearance, maybe as much as 0.050). All of the linkages appear to be OK and not restricting the throttle motion. If anything, the cruise and throttle valve cables see to be almost too slack at the idle stop.

    Thanks.
    dac675

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    Re: '92 Seville 4.9 questions

    Have you read the following series of posts...??? I wonder if the RPM hanging too high could be the same problem in your case...i.e..the TCC/VCC solenoid in the trans having failed in a fashion that it is not releasing the lockup torque converter as you slow to a stop and that is holding the RPM up and not allowing it to come down...???


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