97 Deville Running poorly Help.
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Northstar Engines and System Technical Discussion Discussion, 97 Deville Running poorly Help. in Cadillac Engine Technical Discussion; ...
  1. #1
    Nickcruffin is offline Cadillac Owners Member
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    97 Deville Running poorly Help.

    I have a 97 Deville with 4.6 liter N* engine --- the car will run ok for half a day or so 50 to 60 miles then it decades the act like it is running out of gas, then stops one to 3 minutes later it starts and runs ok again. Note: I don’t think that it is running correctly the gas mileage has slipped to only 16 mpg. It all started with a po171 174 and 131 134 engine fault. I replaced fuel filter, the O2 sensors bank 1 and 2 later the MAF sensor and then the TPS. each seamed to help for a while.



    Also note that in the midst of this the starter went out and I replaced that . I removed the intake manifold and replaced the starter myself.



    The problem still persist and is getting worse. this morning the car ran only 10 minutes before it started running rough and slowed down to a crawl. Note, when the car acts up it starts by loosing acceleration then slows to idle at 5 to 10 mph. If I quickly push the accelerator peddle to the floor twenty to thirty times it will slowly get up to 25 or 30 then I back off and the car will maintain that speed. today I did that and the car got back up to speed the ran good for 20 minutes. I just replaced the fuel filter for the second time and it was ok.



    yesterday the car just lost power while I was running at 70mph I pulled over to the shoulder and the car died. I waited 2 or 3 min. then started the car and it ran ok.



    I am running out of stuff to replace does anyone have any suggestions.

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  3. #2
    eldorado1 is offline Cadillac Owners Connoisseur
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    Re: 97 Deville Running poorly Help.

    Since you've replaced everything else... maybe it's time to look at the fuel pressure regulator?

  4. #3
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    Re: 97 Deville Running poorly Help.

    Put a fuel pressure guage with a long hose on it and tape it to your windshield. See what happens when the problem appears. I suspect you will see falling fuel pressure. I had a similar problem with a '92 Deville and it turn out to be the fuel pump.

  5. #4
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    Re: 97 Deville Running poorly Help.

    Yep....check the fuel pressure. There is a schraeder valve fitting on the fuel rail to hook up a fuel pressure gauge. Find an old R12 refrigerant charging connector/adaptor hose. The fitting on the end for R12 systems is the same as the fuel pressure schraeder valve. Find an old gauge and hook it up to the hose and tape it so that you can see it while driving. The fuel pressure should stay constant at about 50 PSI at idle , stay constant during accel and go up by about 2-3 PSI as you go to WOT. If it drops or is unstable start thinking fuel pump.

  6. #5
    Nickcruffin is offline Cadillac Owners Member
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    Re: 97 Deville Running poorly Help.

    Thank you, Thank you, Thank you. I have had several people tell me that it was not the Fuel Pump but i have thought that for a long time. --- thanks for telling me about the old refrigerant. I think i have some of that stuff left over if i can find it. Thanks again.

  7. #6
    Nickcruffin is offline Cadillac Owners Member
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    Re: 97 Deville Running poorly Help.

    Ok. I gave up and took the car to the shop. I thought the fuel pump was acessable throught the trunk floor as it says in the Haynes manual --- it is wrong. So i took it to a Cadillac specialest. We will see tomorrow.

  8. #7
    eldorado1 is offline Cadillac Owners Connoisseur
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    Re: 97 Deville Running poorly Help.

    It's not wrong... It just forgot to mention you need a sawzall.

  9. #8
    Nickcruffin is offline Cadillac Owners Member
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    Re: 97 Deville Running poorly Help.

    No kidding!!

  10. #9
    Nickcruffin is offline Cadillac Owners Member
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    Re: 97 Deville Running poorly Help.

    You will never ever guess what was wrong......


    I had replaced the starter earlear and did not tighten the manafold bolts to 20 lbs. and the intake was sucking air past the gaskets.... I tightend the bolts and the car now runs great and the milage is back.

  11. #10
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    Re: 97 Deville Running poorly Help.

    Man, it is so hard to get good help these days.... LOL LOL

    Glad you found the problem and that it was an easy fix.

  12. #11
    eldorado1 is offline Cadillac Owners Connoisseur
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    Re: 97 Deville Running poorly Help.

    Quote Originally Posted by Nickcruffin
    You will never ever guess what was wrong......

    I had replaced the starter earlear and did not tighten the manafold bolts to 20 lbs. and the intake was sucking air past the gaskets.... I tightend the bolts and the car now runs great and the milage is back.
    97 manifold = 20ft lbs?????? I thought it was like 10 inch pounds or something? (Maybe I should check mine?)

  13. #12
    Nickcruffin is offline Cadillac Owners Member
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    Re: 97 Deville Running poorly Help.

    Where were you yesterday when i needed you. Yes it is 89 inch pounds or 7.4 foot pounds. So i had to do everything over again. and now i think it is fixed. but i am lucky that i did not ruin the manafold at 20 foot pounds. I had to get a new gasket though.

  14. #13
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    Re: 97 Deville Running poorly Help.

    Quote Originally Posted by Nickcruffin
    Also note that in the midst of this the starter went out and I replaced that...
    I thought you got this problem before you changed a starter.

  15. #14
    Nickcruffin is offline Cadillac Owners Member
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    Re: 97 Deville Running poorly Help.

    Well, I did have a P0171 p0174 code before the starter that was why it took so long to discover that the starter was bad too. So when I replaced the starter it took a long time to discover that the trouble was self inflicted. I had the car checked out by a real mechanic and he discovered the leak around the intake manifold. I have since opened up the car again and put some gasket seal on the reusable gasket --- I know I and not supposed to but I must have screwed it up by over torqueing the bolts. But as far as i can tell that did not work --- I only put a very thin coat of seal on the gasket so i a thinking of doing that over with more seal. If that does not work I will get a new gasket and start over. Any thoughts on this????

  16. #15
    Nickcruffin is offline Cadillac Owners Member
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    Talking Re: 97 Deville Running poorly Help.

    Ok! Now I think it is fixed. I had to get another intake manifold and a new set of gaskets. I could not see any cracks in the manifold but I got one from a junk yard and installed it along with all my new parts. The gaskets I removed were junk --- now the car is getting good mileage and so far has not given me any trouble – my fingers are crossed.

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