EGR System Question
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HT4100 4.1, 4.5, 4.9 Discussion, EGR System Question in Cadillac Engine Technical Discussion; Not sure which forum to ask this question. I have an '89 4.5 Seville. I am having problems passing the ...
  1. #1
    mckimjim is offline Cadillac Owners Member
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    EGR System Question

    Not sure which forum to ask this question. I have an '89 4.5 Seville. I am having problems passing the emissions test (high NOX). I've replaced the EGR valve with no change to the NOX level.

    1. Does the EGR valve operate off of vacuum or pressure? I've hooked a hand vacuum pump to the valve and I can't pull a vacuum and get no movement (both old and new valves).

    2. Just behind the EGR valve is a bracket with two modules mounted to it. Each one has an electrical connector attached. The upper module has one hard plastic line that connects to the throttle plate. The lower module has two hose connection points on the drivers side. The upper line is a hard plastic line that connects to the EGR valve. The hose to the lower connection is missing. Should there be a line connected to this? If so, where does it go? I'm hoping this is my problem. On the opposite side of the lower module is what appears to be a diaphragm and then a line that connects to the throttle plate. What are these two modules called? Is there any way I can test these to see if they are operating properly?

    With the engine running (idle) I can push up on the diaphragm and the engine stumbles. I've also replaced the catalytic converter.

    Any comments or suggestions would be appreciated.

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  3. #2
    mckimjim is offline Cadillac Owners Member
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    Re: EGR System Question

    After reading some older posts I think the lower module is the egr solenoid and the unused connection is for a filter. EWII3rd had some good info. I hooked up a vacuum gauge to the egr valve line. At idle I had no vacuum, when I unplugged the electric line I got 10" of vacuum.

    Question: With the line connected to the EGR valve, if I unplug the electric line when the car is idleing would this cause the EGR valve to open and cause the engine to stumble? When I do this nothing happens.

    Thanks,

  4. #3
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: EGR System Question

    I think that EGR valve is operated by vacuum & back pressure if I recall correctly. The PCM controls the solenoid & valve which apply vacuum to the EGR valve. The nipple with not hose on it MIGHT be a vent port, but I am not positive. It has been a long time since I had one of those. A FSM would explain how it operates. That said, I am going to move this thread to the 4.1, 4.5 & 4.9 section where you may get more help.

    Question: With the line connected to the EGR valve, if I unplug the electric line when the car is idleing would this cause the EGR valve to open and cause the engine to stumble? When I do this nothing happens.
    No. There is no, nor should there be any EGR vacuum at idle. You proved that by putting your finger underneath and raising the pintle, thus applying EGR at idle and causing the engine stumble.

  5. #4
    HUF's Avatar
    HUF
    HUF is offline Cadillac Owners Connoisseur
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    Re: EGR System Question

    EGR is is disabled at idle. The third port of the EGR solenoid should not be connected to anything. CLEAN TWO EGR TUBES INSIDE THE THROTTLE BODY (under the plates) WITH A COAT HANGER. If they are plugged with carbon deposits it will affect the emission.

  6. #5
    awadecki is offline Cadillac Owners Enthusiast
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    Re: EGR System Question

    Also replace your oxygen sensor.

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