Hi. I need lots of help concerning the 4.9L. Thanks. - Page 2

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HT4100 4.1, 4.5, 4.9 Discussion, Hi. I need lots of help concerning the 4.9L. Thanks. in Cadillac Engine Discussion; You mentioned that when the engine is off the ISC plunger is keeping the Throttle Body Blades (butterflies) cracked open. ...
  1. #16
    peteski is offline Cadillac Owners Enthusiast
    Automobile(s): 85 Eldo Biarritz
    Join Date
    Dec 2003
    Northeast USA

    Re: Hi. I need lots of help concerning the 4.9L. Thanks.

    You mentioned that when the engine is off the ISC plunger is keeping the Throttle Body Blades (butterflies) cracked open. Maybe that is your problem.

    I'm not sure about 4.9 engine. On my 4.1 engine I can enable solenoid cycling mode from the self-diagnostics. That cycles all solenoids (including full extension and retraction of the ISC). I think if the ISC solenoid is fully retracted, it should not be touching the throttle lever.

    Maybe the ISC plunger is out of alignment. I can adjust mine by turning the plunger (it is threaded, so it can be adjusted). Again in the 4.1, there is also a screw which controls the full clousure of the throttle body blades. But if that was out of alignment, the ISC plunger would probably not be in contact with the throttle lever.

    My Service manual also shows how to fully retract the ISC plunger. Basically, you keep the ISC plunger depressed with your fingers (therefore keeping the idle switch closed) while pulling the throttle lever up (therefore increasing the rpms of the engine). The PCM thinks your foot is off the throttle so it tries to decrease the engine rpms by retracting the ISC plunger. This is all done when the engine is running of course.

    But since your engine is reving way too high, I suspect that PCM already tried to fully retract the ISC.

    So, you might need a new ISC or possibly PCM...

  2. #17
    lou91sts is offline Cadillac Owners Member
    Automobile(s): 91 Seville STS
    Join Date
    Feb 2009
    Lewiston, Maine

    Re: Hi. I need lots of help concerning the 4.9L. Thanks.

    I can't be of much help in answering your current question but I wanted to chime in and say that I am following along because I am having similar issues with my 91 STS, 4.9l. I have owned it one year and put 10k miles on it to bring it to 67,000. I run mid grade 89 oct. and get 18mpg in town, 28+ on the open road up to 60 mph and about 24 mpg cruising at 75 mph (just for comparison).
    I have replaced all plugs and two forward O2 sensors. I have cleaned (sprayed) the intake but have not rodded the egr tubes, currently it idles fluctuating at 575-650. I will do that later today.
    I still have a issue with the way it runs. I feel it is poor spark because I can feel it no matter the engine speed. Wires and rotor should fix it.
    My contributions to your questions are:
    After replacing the O2 sensors I had extreme rough idle. My mechanic informed me that the first generation OBD (on board diagnostics) takes two full drive cycles to re-learn. be sure to allow for getting up to running temp and full cool down twice and after that apon starting you should see a change. That was my experience.
    I did remove a hose to get at one plug. It is possible but requires patients and scrapped knuckles, unless you remove more of whats in the way.
    Let me know if yours has the CCR, air struts. I just replaced mine with Monroe Sensa Trac and they ride fine. I believe that it is not as good a ride a s before but worth the cost savings ($120 ea. over $440 ea).
    At the same time I had the rack and pinion steering assembly replaced to leaking seals. New parts were a better deal than re-built with my mechanic doing the labor.
    Thanks, the thread has been very good for me also.

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