Troubles with the 77 CDV
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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; If you've been following my travel thread in the lounge, you know that my road trip got cut short by ...
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    77CDV's Avatar
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    Unhappy Troubles with the 77 CDV

    If you've been following my travel thread in the lounge, you know that my road trip got cut short by car trouble. I'm wanted to post in here to see if anyone has some ideas, because I'm stumped right now.

    The car ran great from LA to Boston. Interstate highway travel, sustained speeds of 65-70, elevation changes from sea level to 8000 feet and back down. All normal stuff and no issues. However, after leaving Boston and running for about two hours at interstate speed, the car started bucking like it was starving for fuel. I stopped, let it cool down, checked what I could, and couldn't find any issues. The carb is getting fuel (low pressure aux electric fuel pump installed last year to combat vapor lock) and there is spark to all cylinders. I tried going on, but the condition recurred.

    The car runs well at lower speeds, idles smoothly, and though it will die with this condition if pressed, it will start right back up with no delay.

    Thoughts?

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    1980coupe's Avatar
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    Re: Troubles with the 77 CDV

    Clogged fuel filter...???

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    amunderdog is offline Cadillac Owners Connoisseur
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    Re: Troubles with the 77 CDV

    catalytic converter?
    They claim you can use one of those fancy thermometers that you point and shoot.
    Check the inlet temp versus outlet temp.
    There are a few other ways to test one.

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    cadillac_al is offline Cadillac Owners Connoisseur
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    Re: Troubles with the 77 CDV

    I'm stumped. The car is undriveable due to bucking. Is this a CA emission vehicle? On newer fuel injected cars (Buick 3.8) a malfunctioning EGR will make it buck. I can't recall having a bucking condition with any of my old cars in the past. It doesn't sound like ignition cutting out or it would backfire. Will it rev up in neutral? Can you watch the secondaries kick open with the air cleaner removed? It must be starving for fuel for some reason. Is there any way to disconnect a line to see how strong the fuel flow is? I hope the filter sock in the tank isn't clogging up. Just for kicks I would try unplugging the EGR and see what happens. There is a good chance this could all be emission related. I think if fuel flow is low, it may buck but I don't think it would necessarily stall. I would think the engine would catch itself once the rpms dropped and continue to idle. I hope unplugging the EGR will do something for it. Good luck.

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    Re: Troubles with the 77 CDV

    It is a CA car. I'm leaning toward something emissions-equipment related. Fuel flow is good, secondaries open normally, revs fine in neutral, no evidence of backfiring. It does seem to be running a little rich, but nothing extreme. The only time I've seen a car act this way is due to exhaust backpressure choking the engine, but why would the car only have a problem after extended cruising?

    I'm having the car shipped back to CA, because I just don't have the resources to deal with it properly 3000 miles from home. I'm just trying to get a few more people thinking about the problem to see if I'm completely off base in my thinking.

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    Re: Troubles with the 77 CDV

    Over rich could have killed the cat. If it were me, I'd cut it out, put in a straight pipe, and get home. At least it won't cost much to find out (even if you have to buy a sawzall). I know you have to deal with CA emissions, so get a new cat when you get there.

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    Craig, sorry to hear about this. It is all part of the fun and adventure of driving an old car cross country isn't it! I hope you get things squared away in a hurry!

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    outsider is online now Cadillac Owners Connoisseur
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    Re: Troubles with the 77 CDV

    I agree with Jay, cut out the cat and see if you can make it back like that. The cost will be way cheaper than having the car shipped.

    I don't think it's the EGR because any time I've had EGR trouble it would happen no matter what the driving condition, and more so at low speeds and idle was very rough.

    It is odd that it runs fine at lower speeds but only bucks and dies when at highway speeds though...very confusing situation.

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    lacville78 is offline Cadillac Owners Fanatic
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    Re: Troubles with the 77 CDV

    This is strange, how would a plugged cat affect the engine operations at speed? It seems like if it is clogged, it is clogged regardless of how fast the car is going. I could see it affecting performance at certain engine r.p.m.'s but that would happen going through all of the gears.

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    Re: Troubles with the 77 CDV

    A clogged cat can sometimes act worse when hot. A manifold vacuum gauge will prove an exhaust restriction. If vacuum drops with steady 1800-3000 RPM engine fully warmed up there's a restriction. More revs lower vacuum.

    My guess is if the booster pump is just inline with the factory pump it's the factory pump's pressure relief valve. Diagnosis is to pinch off the smaller return hose and take it for a blast.

    The other one that could fit would be the HEI pickup connection to the module is just about broken in half. You did not mention backfiring though.

    Good luck.

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    lacville78 is offline Cadillac Owners Fanatic
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    Re: Troubles with the 77 CDV

    Ok so when it is warmed up why wouldn't the car act bad in first or second gear, wouldnt the rpms be the same as third?

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    Re: Troubles with the 77 CDV

    Quote Originally Posted by lacville78 View Post
    Ok so when it is warmed up why wouldn't the car act bad in first or second gear, wouldnt the rpms be the same as third?
    Plugged cats can be elusive. They are not usually completely plugged. Temperature makes a lot of difference. Exhaust restrictions pretty much destroy the vacuum signal to the carbonator's metering rods.

    All kinds of unexpected things can happen with a bad cat.

    I'm still not sold that this is his problem though.

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    Re: Troubles with the 77 CDV

    I'm not the most knowledgeable but im wondering if maybe when the car reaches speed on the highway if the emissions system is trying to suck through the charcoal canister and it is plugged causing trouble at highway speeds.

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    Lol! Great minds think alike. Just now found this thread, But I was talking to Craig after it happened on the phone & we came up with about all the same ideas posted here. Initially thought carb flooding or restricting, I thought it was strange how it only happened at a certain speed, and not with the rpm through shift changes, suggested bad cat converter & discussed rich running & back pressure.

    The mechanic he found said it was the egr valve, tried to order a new one (cleaning not attempted), ended up receiving just a gasket (these cars don't even have an egr gasket, unless fuel injected). Mechanic said he bypassed it sent Craig on his way. Problem arose again after roughly 3 hours of driving, on the bridge connecting New York to Jersey of all places. No mention I could find in the service manual diagnostics about an egr valve causing this kind of problem.

    Stumped. Still thinking cat or carb, but very curious what the 11 toed mechanic did to the egr valve...
    77CDV likes this.

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    Re: Troubles with the 77 CDV

    Looks you all are thinking along the same lines I am. I'll be interested to see what I can find once the car gets home.

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