4.5 Liter - Last chance before I need to give it up.
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HT4100 4.1, 4.5, 4.9 Discussion, 4.5 Liter - Last chance before I need to give it up. in Cadillac Engine Technical Discussion; Hello All So, here is my last attempt to hopefully figure something out... I had a month ago bought my ...
  1. #1
    88_Deville_Executive is offline Cadillac Owners Member
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    4.5 Liter - Last chance before I need to give it up.

    Hello All

    So, here is my last attempt to hopefully figure something out... I had a month ago bought my 89 Coupe Deville. Through a few previous posts... and finally
    taking it into a mechanic I learned a few things but also don't have alotta cash here so I am against a wall to get rid of this and end up going to something more reliable or easier to fix I guess... The reason its my last chance is I sold my other caddy thinking this would be easier than I thought. I have to borrow the inlaws truck and need to give it back shortly... and am short on cash for something else..but need to make the move here.

    My car has a problem idling. I took it into a exhaust place. Did a back pressure test and the cat. was bad.. but of course something else was the cause. Paid 100 bucks @ a mechanic... one of the plug wires was disconn.. and he reconn. it and it ran alot better, but still had a miss under load.

    I put some seafoam in the tank the other day. While not sure that it actually helped, here is the deal... it seems to idle really nice and drive well for the first few min.. then maybe after it has warmed up.. it seems to have a rough idle, maybe a miss or something.

    When I am in drive, and even park, it has this shaking, and you can tell that it wants to die so the ISC kicks up the idle for a moment. Again, only when its warmed up it seems.

    I have tested the following so far. MAP sensor; changed out the cap and rotor. Sprayed the plug wires for arching (nothing)... have watched the two injectors and noticed no dripping or anything odd. Again, cat IS bad.

    The mechanic said it needed a full tune-up, but he seemed alittle off base cause he claimed the cap and rotor was bad though I replaced it just a few weeks previous. They wanted to charge me close to 500 bucks for the simple tune.

    I am sorta at wits and cash's end. I am scared of putting any more funds into it just because my wife is mad at me for getting another "bad" caddy. :-(

    Please help- any other recommendations? I could still replace the wires I guess but it does not sorta seem to cause intermittent issue? I was able to move the egr value so it does not seem "crusted or anything". The throttle body is also really clean. Car only has 115K miles.

    Thanks for info.,,

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  3. #2
    cadillac_al is offline Cadillac Owners Connoisseur
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    Re: 4.5 Liter - Last chance before I need to give it up.

    Did you ever replace the cat? No matter what kind of used car you buy, it's usually a good idea to give it a tune up. If you don't do mechanic work then you should have a regular mechanic that you can trust and not be at the mercy of just any mechanic. If you already replaced the cap and rotor, then all you need is a set of plugs. If the cat is clogged it will never run right and it does have 115,000 on it. It should be a fine car with some routine maintenance. Good luck

  4. #3
    awadecki is offline Cadillac Owners Enthusiast
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    Re: 4.5 Liter - Last chance before I need to give it up.

    If your problem only occurs when hot, it may be the oxygen sensor. They're about $20 and located in the exhaust manifold. Try replacing that. If that sensor isn't working properly, it'll also cause the cat to go bad.

  5. #4
    El Dobro's Avatar
    El Dobro is offline Cadillac Owners Connoisseur
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    Re: 4.5 Liter - Last chance before I need to give it up.

    Have you checked the timing?

  6. #5
    90devilleguy's Avatar
    90devilleguy is offline Cadillac Owners Enthusiast
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    Re: 4.5 Liter - Last chance before I need to give it up.

    probably the ecu is f'd. have someone run a test on the pulse on the injectors and see if one or a few injectors are not getting the correct voltage from the ecu. It happened to me before on my 4.9 eldo. Horrible skipping.....it was the ecu....

  7. #6
    HUF's Avatar
    HUF
    HUF is offline Cadillac Owners Connoisseur
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    Re: 4.5 Liter - Last chance before I need to give it up.

    I would definitely look at the ECM (the computer). The mechanica you took the car too seem to be not familiar with Cadillacs. BTW, did you check for trouble codes?

  8. #7
    ammonia11 is offline Cadillac Owners Member
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    Re: 4.5 Liter - Last chance before I need to give it up.

    Check the ground bolt on the block near the starter. That is a common problem for these cars. The ground causes intermittent stuttering, especially if you put the electrical system under a load. The fuel injection system will try to overcome the problem and it will run rich. The comp will show you are getting about 2 mpg I bet. You will probably have to replace the catalytic converter after this fix since it will probably be plugged with soot. Once again, this is a very common problem. Loosen, and then clean the stud, nut, and eyelets. Then tighten. Good luck. Michael.
    Quote Originally Posted by 88_Deville_Executive View Post
    Hello All

    So, here is my last attempt to hopefully figure something out... I had a month ago bought my 89 Coupe Deville. Through a few previous posts... and finally
    taking it into a mechanic I learned a few things but also don't have alotta cash here so I am against a wall to get rid of this and end up going to something more reliable or easier to fix I guess... The reason its my last chance is I sold my other caddy thinking this would be easier than I thought. I have to borrow the inlaws truck and need to give it back shortly... and am short on cash for something else..but need to make the move here.

    My car has a problem idling. I took it into a exhaust place. Did a back pressure test and the cat. was bad.. but of course something else was the cause. Paid 100 bucks @ a mechanic... one of the plug wires was disconn.. and he reconn. it and it ran alot better, but still had a miss under load.

    I put some seafoam in the tank the other day. While not sure that it actually helped, here is the deal... it seems to idle really nice and drive well for the first few min.. then maybe after it has warmed up.. it seems to have a rough idle, maybe a miss or something.

    When I am in drive, and even park, it has this shaking, and you can tell that it wants to die so the ISC kicks up the idle for a moment. Again, only when its warmed up it seems.

    I have tested the following so far. MAP sensor; changed out the cap and rotor. Sprayed the plug wires for arching (nothing)... have watched the two injectors and noticed no dripping or anything odd. Again, cat IS bad.

    The mechanic said it needed a full tune-up, but he seemed alittle off base cause he claimed the cap and rotor was bad though I replaced it just a few weeks previous. They wanted to charge me close to 500 bucks for the simple tune.

    I am sorta at wits and cash's end. I am scared of putting any more funds into it just because my wife is mad at me for getting another "bad" caddy. :-(

    Please help- any other recommendations? I could still replace the wires I guess but it does not sorta seem to cause intermittent issue? I was able to move the egr value so it does not seem "crusted or anything". The throttle body is also really clean. Car only has 115K miles.

    Thanks for info.,,

  9. #8
    ammonia11 is offline Cadillac Owners Member
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    Re: 4.5 Liter - Last chance before I need to give it up.

    Check the ground stud on the block near the starter. A very common problem with these cars. The cat will probably be plugged with soot by now. (comp trys to overcome the problem, so fuel milage goes down to about 2mpg I bet). This ground needs to be cleaned, and retightened. Disconnect the battery prior to this fix! Mike.

  10. #9
    NickySantoro is offline Cadillac Owners Fanatic
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    Re: 4.5 Liter - Last chance before I need to give it up.

    OP,
    How old are the plugs and wires?

  11. #10
    hthorn is offline Cadillac Owners Member
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    Re: 4.5 Liter - Last chance before I need to give it up.

    It'll help to ask yourself why the cat failed in the first place. The oxygen sensor is a good place to start; you can test it with a meter set to the millivolts scale. If the sensor does not fluctuate between .1 and .9 rapidly after the engine has reached normal operating temperature, then it should be replaced. However, any misfire which causes unburned fuel to escape thru the exhaust valves will soon foul the new one. You can use a vacuum gauge to pinpoint this further. Also a defective coolant temperature sensor could contribute to this problem. Try the oxygen sensor first, since it sounds like it runs OK until it goes into closed loop. It may also be worthwhile to connect an analog tachometer to the TACH terminal on the distributor, so you can see the idle speed reading. Tune it according to the instructions on the hood label or Haynes/Chilton. Make sure the radiator cooling fans come on at least once BEFORE you adjust it; you'll need to watch the idle speed before and after they come on, since the ISC will have to raise the idle a bit to compensate. 800-1000 RPM is all you should see. Any higher is too much, and will cause many other problems down the road, such as a broken front motor mount or TCC faults. Often idle speeds on these engines "drift" upward as they age. A digital tachometer will not have a high enough sample rate to be of much use, which is why an analog tach is preferable.

  12. #11
    Romy is offline Cadillac Owners Member
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    Re: 4.5 Liter - Last chance before I need to give it up.

    It seems I got the same problem. How did you solve yours? ECM? CAT? I got a '88 Fleetwood

    thanks

  13. #12
    illumina's Avatar
    illumina is offline Cadillac Owners Connoisseur
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    Re: 4.5 Liter - Last chance before I need to give it up.

    A spud bar will normally take care of a catalytic converter. Please observe state laws before doing this.


  14. #13
    guidematic's Avatar
    guidematic is offline Cadillac Owners Fanatic
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    Re: 4.5 Liter - Last chance before I need to give it up.

    I concur on the tune up. If you have a "new" car that you do not know the service history, then you should maker this one of the first things to do. Along woth an oil change.

    Normally when people deside to sell a car, they go lax on the maintenance. So. it's a good base line to start with. Then if the problem persists, you can look in other areas knowing that basic manitenance has been done.

    Mike

  15. #14
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    mikeythegreek is offline Cadillac Owners Member
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    Re: 4.5 Liter - Last chance before I need to give it up.

    if you replace sensors make sure you get ac delco parts too, other stores sell stuff that just dont cut it. Ive had an egr valve cause similar problems - it was new but not a delco, same thing with Oxygen sensor, just wasnt right so got a delco and then it was right.

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