1990 bougham lack of power surging on hills please help
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5.0 and 5.7 Discussion, 1990 bougham lack of power surging on hills please help in Cadillac Engine Technical Discussion; ...
  1. #1
    johnwas is offline Cadillac Owners Member
    Automobile(s): brougham with 5.7 1990
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    1990 bougham lack of power surging on hills please help

    i have a 1990 brougham with the 5.7 and it seems to fall on its face when i step on it and surges on hills and has general lack of power has apx 150,000 miles

    heres whats be done so far
    throttle body was replaced gm delco new in box with injectors and sensors
    AC (came with throttle body)
    tps (came with throttle body)

    new cap and rotor , plugs oem's

    egr valve ( it was bad )

    map sensor got 4 at junk yard have tried them all same readings

    oxygen sensor last winter

    new ac pump

    OK heres what I have checked

    vac readings with all other vac lines plugged ( was looking for vac leak none found readings the same with all hooked up)

    20 “ at idle drops way down to about 2” when it is revved up fast
    I thinks this has some thing to do with the problem
    on the road
    runs about 17” till on hill
    then down to 5”

    all most no blow by

    compression
    runs 150 lowest to 170 highest

    timing is advanced to about 12 degs spec calls for 0 degs
    reset to spec and it
    ran much worse so set back to 12 advanced

    mpg is low to about 16 mpg highway

    though there might be a plugged catalytic converter
    that's new too
    any tests I should do or some thing iam missing
    as iam about
    to pull in take a replace with edlebrock 4 barrel carb

    i have a code readed that can capture live data too
    no code present please help chaseing this gremlin is driving me nuts

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  3. #2
    sven914 is offline Cadillac Owners Connoisseur
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    Re: 1990 bougham lack of power surging on hills please help

    When you did the timing, did you disable the computer spark advance? That would mess it up if you didn't.

    The vacuum should quickly drop to around 0 when you rev the engine (that is a normal condition) but the needle should slowly return after that. When you release the throttle, the needle should jump to around 30 inches. As you're driving, you are holding the throttle plate slightly open, so the vacuum will drop a little, and you need to lay into it more to make the hill, so the 5 inches is also normal.

    Change the fuel filter and see if that corrects anything. I assume you changed the plug wires when you did the tune up, but did you change the ignition module? Also a bad coolant sensor can cause similar problems.

  4. #3
    johnwas is offline Cadillac Owners Member
    Automobile(s): brougham with 5.7 1990
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    Re: 1990 bougham lack of power surging on hills please help

    thats a no on the plug wires and coil i ohmed them and they checked fine

    also i replace the fuel pump about 3 weeks a ago as it when out
    about 30 miles from home the fuel filter was change then too ( first with hope )

    and on the timming i did it how the dealer service manual said
    jumper a and b on the aldl


    thanks for your input if there is some thing i should check please let me know

    i was thinking maybe i would put on a hot coil and see if any change

    the cars seems to have lots of power when below about 25 mph
    can burn the tires

    just looses it on the high end ps

    new trans + torc converter last winter od has been beefed up as
    i have been chasing this grimlin for a while

    could the ecm be causeing this the weird thing is when
    the scan tool is plugged in it runs a little better and has high idle

    as for the coolent sensor i have been watch the temp with it
    call me paranoid but i just dont trust dumy lights and i have in stalled
    an extra temp gauge and they run very close with in 10 - 20 degs
    temp gauge is in the themostat housing sensor in manfold

    i also is some inprovement when i unplug the egr

  5. #4
    N0DIH's Avatar
    N0DIH is offline Cadillac Owners Master
    Automobile(s): 94 Fleetwood Brougham
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    Aug 2004
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    Re: 1990 bougham lack of power surging on hills please help

    Most often surging is caused by lean fuel mixtures.

    A plugged cat will show rich on the O2 and the PCM will lean it out further to make it look correct on the O2. Depending on where the O2 is, if you can remove it and run it, without catching the car on fire, see if it is better.

    Or find an exhaust shop to do a pressure test and see if it the cat is plugged up. With EGR unplugged and it running better makes me suspect the mixture is lean. Is O2 reading good? Don't replace for no reason, datalog it somehow and make sure it is ok or not ok. Autozone has a handheld that you can use and see if the O2 has sufficient activity. It won't always set a code, but it does need a good amount of cross counts.

    You can unplug the O2 sensor connector and drive too, see if that helps, then it isn't going on O2 sensor feedback, so the fuel mixture should be better, but might show the "rich" reading the cat converter plugged often shows.

  6. #5
    sven914 is offline Cadillac Owners Connoisseur
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    Re: 1990 bougham lack of power surging on hills please help

    The plug wires could have good resistance, but still be crap, so replace them.

    Grounding the ALDL is another way to make the computer stop correcting the ignition timing. The car might run better with the scanner connected or the ALDL grounded because the computer is in default fuel mode. In default mode, the computer is dumping fuel into the engine (a super rich mixture), so N0DIH is probably right about the lean running condition.

    There are two coolant sensors on the engine. One is for the idiot light on the dash and the other tells the computer the engine's temperature. If the sensor for the computer is malfunctioning and reading too hot or too cold, the computer will play with the fuel mixture, which can cause poor drivability and performance.

  7. #6
    N0DIH's Avatar
    N0DIH is offline Cadillac Owners Master
    Automobile(s): 94 Fleetwood Brougham
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    Re: 1990 bougham lack of power surging on hills please help

    When you do a cold start from overnight sit, the intake air temp sensor (IAT) and CTS (coolant temp sensor) should be close to the same value. Ohm them out with a meter if you can.

    Sometimes when I think the IAT or CTS is a problem I will put a resistor in them and make the reading what I want, just hardcode the sensor's reading to the PCM.

    I am still a fan of GM spec'd wires or a higher end wire. The resistance in my book is almost meaningless, the voltage drop at those voltages it takes an awful lot of resistance to make a diff in power, not a few k ohms. I have had junk wires also ohm good but still not be able to carry the current needed to complete good combustion. A good wire like a set of Magnacor's is well worth it. Those are great wires....

    But I also like solid core wires too... plain jane stranded wire......

    Quote Originally Posted by sven914 View Post
    The plug wires could have good resistance, but still be crap, so replace them.

    Grounding the ALDL is another way to make the computer stop correcting the ignition timing. The car might run better with the scanner connected or the ALDL grounded because the computer is in default fuel mode. In default mode, the computer is dumping fuel into the engine (a super rich mixture), so N0DIH is probably right about the lean running condition.

    There are two coolant sensors on the engine. One is for the idiot light on the dash and the other tells the computer the engine's temperature. If the sensor for the computer is malfunctioning and reading too hot or too cold, the computer will play with the fuel mixture, which can cause poor drivability and performance.

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