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RWD 19xx-1984 DeVille and Fleetwood,
1985-1996 Fleetwood and Brougham Forum Discussion, Troubles with the 77 CDV in Past Cadillac Vehicle Discussion; My fingers AND toes and arms and legs are all crossed for you Craig!...
  1. #61
    Bro-Ham's Avatar
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    My fingers AND toes and arms and legs are all crossed for you Craig!

  2. #62
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    Re: Troubles with the 77 CDV

    Quote Originally Posted by Bro-Ham View Post
    My fingers AND toes and arms and legs are all crossed for you Craig!
    Sounds like you won't be going anywhere fast with all that!


    Thanks, Dave.

  3. #63
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    Re: Troubles with the 77 CDV

    The problem with having a shop diagnose this is they need to make a profit for their time. Your problem is not constant and requires a warm-up and test drive.

    I hope they finally get it.

    Best of luck.

  4. #64
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    Re: Troubles with the 77 CDV

    Good luck!
    77CDV likes this.

  5. #65
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    Baffling issue. I have one of those in my old vette, I'm down to it being a fuel system issue. At least I hope it's a fuel feed issue .

    I've driven 425's Hundreds of thousands of miles, never experienced this.

    On another note, I never saw 18. MPG either not even downhill with a tailwind. 18? Someone is feeding exhaust into the interior.

  6. #66
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    Re: Troubles with the 77 CDV

    First mistake is disconnecting the EGR valve. It needs to work for max fuel economy. Sorry so many of you guys belong to the friends of OPEC club.

  7. #67
    csbuckn is offline Cadillac Owners Master
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    My money is on the egr or cat also. Maybe get it to repeat the problem and take the temp before and after the cat. I'd also do the vacuum test to test the egr valve also. The egr feeds right off the cat converter, right? Does it hesitate a little off the line?

  8. #68
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    Come to think of it, I did have somebody put a plug in place of the EGR in an LT1. That caused a similar issue. That's easy to test, Just pull the EGR off the valve cover and take it for a ride. Cover it or you will have a big Oily mess on your hands.

    Once I drove the LT1 with that issue for a while, the vacuum pressure buildup inside the motor made it buck, cough and stall but it took 20 minutes or so. It was over pressurizing the crankcase.

    I do recall having some bizarre EGR problems with some of my 1977 sedan Deville's. the giant poof of blue smoke going up a steep hill every now and again was a real stumper to figure out.

  9. #69
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    Re: Troubles with the 77 CDV

    It isn't the EGR in this case. He already went down that road. I mentioned that only for the fuel economy scoffers.

    Hey did you guys see my fly by while you were stopped at the gas station?

  10. #70
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    Re: Troubles with the 77 CDV

    Quote Originally Posted by The Ape Man View Post
    First mistake is disconnecting the EGR valve. It needs to work for max fuel economy. Sorry so many of you guys belong to the friends of OPEC club.
    ... no..... EGR actually measurably reduces fuel economy, on all older engines. It's particularly obnoxious in diesel engines, but certainly doesn't do anything for performance or fuel economy in a gasoline engine.

    EGR is particularly evil on older high mileage engines because of the amount of carbon deposits it forms, eventually negating its own purpose because carbon deposits in the combustion chamber cause the pre-ignition condition (say that 3 times fast) that results in excessive NOx emissions to begin with.

    Now if everything on the engine was new- that would be a different story. It still would likely not cause a major increase in mileage, but it would definitely not cause as big of a decrease as a malfunctioning system. PS. most EGR systems are not operating optimally on 30+ year old engines. There are exceptions, of course. But I just replaced an EGR valve on a 22K mile 368 that was leaking.

    The systems used today are significantly better with electronic controls, but the standard vacuum operated EGR valve on pre-computer cars ONLY helps reduce NOx emissions (which is a good thing, don't get me wrong), and does so at the expense of performance and fuel consumption.

  11. #71
    csbuckn is offline Cadillac Owners Master
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    So was the egr valve replaced or tested with a vacuum guage? Can you get a temp gauge on the exhaust? Any original rubber gas lines in the system that may be collapsing when it warms up? Just thinking out loud.

  12. #72
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    I grew up with 77 and 78 deVilles from new, they were 15 MPG max cars even then, I chuckle when I remember my Dad always madly calculating mileage during the gas crisis in 79 so we could make it between rationed fuel ups.

  13. #73
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    Re: Troubles with the 77 CDV

    Quote Originally Posted by akimball442 View Post
    ... no..... EGR actually measurably reduces fuel economy, on all older engines. It's particularly obnoxious in diesel engines, but certainly doesn't do anything for performance or fuel economy in a gasoline engine.
    EGR is part of the fuel system and spark timing calibration. If it is removed the calibration must be maximized. Your theory may be correct but practice requires more than plugging a vacuum line.

    I speak in terms on old Cadillac manufacture engines. Old Cadillac engines do not have issues with carbon deposits in the combustion chambers. The entire innards of most of these engines are usually remarkably clean except intake valve stems which need periodic decarbonization. This holds true for old high mileage engines also. The usual death of a factory 368/425/472/500 is from main bearing slop resulting in low oil pressure to rod bearings.

  14. #74
    deVille33 is offline Cadillac Owners Connoisseur
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    Re: Troubles with the 77 CDV

    Quote Originally Posted by Bro-Ham View Post
    I grew up with 77 and 78 deVilles from new, they were 15 MPG max cars even then, I chuckle when I remember my Dad always madly mileage during the gas crisis in 79 so we could make it between rationed fuel ups.
    I don't want to burst your bubble of observation here, BUT, one of my '77 CDV's got 16.5 mpg on the average and our venerable Bruce Roe has tweaked his efi '79 close to 20. 15 may be common, but it is possible to tweak more out of the beasts.

  15. #75
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    It seems silly to try to get good MPG out of a big block.

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