Cadillac 1969 quadrajet, bad idle
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500, 472, 425, 368 Discussion, Cadillac 1969 quadrajet, bad idle in Cadillac Engine Technical Discussion; Hello My engine is suffering from bad idle. It idles smooth in about 1000 (I don't have tachometer but approximately) ...
  1. #1
    3dfx is offline Cadillac Owners Member
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    Cadillac 1969 quadrajet, bad idle

    Hello

    My engine is suffering from bad idle. It idles smooth in about 1000 (I don't have tachometer but approximately) rpm, but when I try to lower my rpm, engine starts to shake, smoke more than before and run bad idle. I think my idle is too rich. Is there any kind of adjustment for idle mixture? I think I could get my engine idle smoother if I could lean idle mixture.

    Is there any possibility to lean it in q-jet? What are those two adjusting screws in front of carburetor?

    My ignition timing is ~7-degrees BTDC without vacuum advance in idle.

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    deVille33 is offline Cadillac Owners Connoisseur
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    Re: Cadillac 1969 quadrajet, bad idle

    You mean the 2 small screws near the base of the carb? Those are the air/ mix screws. You have to have the car close to it's base idle speed to set those. They have an influence on idle, but should not make idle erratic. Go back to the exhaust and check out the exhaust pulse. Smoke, is it black, blue, or white? Exhaust pulse at it's best should be a steady flow. If, at low idle, you are getting small explosions (pomm, pomm, pomm) You have a possible cross fire in the ignition. Black exhaust and erratic timing to the exhaust note, the carb is dumping fuel and the excess is most likely firing in the exhaust manifolds upon hitting the exhaust from the adjacent cylinders. This can also be the case of an exhaust valve not fully seating and the excess burning off. You should do a compression test to determine the condition of your cylinders sealing.

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    3dfx is offline Cadillac Owners Member
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    Re: Cadillac 1969 quadrajet, bad idle

    Smoke, is it black, blue, or white?
    Smoke is blue, I think.

    It doesn't smoke lot but I can see it if I look into exhaust. It still smells a lot. Something is wrong with ignition cables or gas/air mixtures.

    If, at low idle, you are getting small explosions (pomm, pomm, pomm) You have a possible cross fire in the ignition.
    There is some small explosions. My car sounds like those with lots of power and high rpm camshaft. I'll have to check my ignition cables.

    I forgot to mention that I have dual exhaust without H- or X-pipe.

    I talked with my friend today and he said making H- or X-pipe could help. He had similar problems with old Ford Cologne V6 and X-pipe helped him.

  5. #4
    cadillac_al is offline Cadillac Owners Connoisseur
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    Re: Cadillac 1969 quadrajet, bad idle

    How old are the points and condenser? They can't be trusted after a year or two.

  6. #5
    deVille33 is offline Cadillac Owners Connoisseur
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    Re: Cadillac 1969 quadrajet, bad idle

    Blue smoke is an indication of oil use. You see this on start-up, and then it fades? If this is the case, the valve oil seals or valve stem wear are possible suspects. More constant, something is wrong with the rings or pistons.

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    3dfx is offline Cadillac Owners Member
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    Re: Cadillac 1969 quadrajet, bad idle

    How old are the points and condenser?
    About half year old.

    You see this on start-up, and then it fades?
    There is a cloud of smoke in startup and if i look into exhaust when the car is idling, I can see smoke coming all the time. Smoke can only be seen when i look into exhaust, it can't be seen if i just look at the back of the car.

    My car also burns lots of oil 1 litre/1000miles.....

    Could this oil burning cause my car bad idle?

  8. #7
    cadillac_al is offline Cadillac Owners Connoisseur
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    Re: Cadillac 1969 quadrajet, bad idle

    The oil burning could possibly be fouling the plugs. You should take a look at a couple of them. It could be the carb too, but it's hard to say without hearing it. I guess you could play with those idle mixture screws. They are generally 3 - 31/2 turns out. Don't turn them in too tight when seating them to count turns. They can be damaged if they are turned in too tightly; just lightly seated.

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    deVille33 is offline Cadillac Owners Connoisseur
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    Re: Cadillac 1969 quadrajet, bad idle

    That is a considerable amount of oil use for one of these engines. I would do a compression test to see if the problem could be narrowed down to one general area. Does the smoke come from one pipe more than the other, or equally from both pipes?

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    Re: Cadillac 1969 quadrajet, bad idle

    Make sure you check the spark plugs of all cilinders to identify the one cilinder that is causing the irratic rpm. Then continue to pinpoint the cause: spark plug, wire, oil, valves...

  11. #10
    3dfx is offline Cadillac Owners Member
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    Re: Cadillac 1969 quadrajet, bad idle

    Sparkplugs in all cylinders look good. None of them is wet, black or anything like that.

    I separated my ignition wires from each other and engine ran smoother and exhaus gasses smelled "good".

    I ordered new ignition wires from my local dealer..See if those will repair my problems.

  12. #11
    3dfx is offline Cadillac Owners Member
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    Re: Cadillac 1969 quadrajet, bad idle

    I have those new wires now. They didn't help my problem.

    My caddy idles worse than before. Lots of blue smoke coming out from the exhaust when idling, when Im accelerating, my car will "shoot in exhaust" a loud bang and black smoke comes out.

    Could it be that my intake manifold gasket is leaking from lifter valley both oil and air? I think that would explain the blue smoke coming out from engine bad running.

  13. #12
    deVille33 is offline Cadillac Owners Connoisseur
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    Re: Cadillac 1969 quadrajet, bad idle

    It is possible for the intake gaskets to have fatigued, but that is usually caused by expansion/contraction and/or corrosion from the engine coolant going to acid and eating through the gaskets. The black smoke and the manner of operation you describe suggests a timing/carburation problem. It could be your timing chain needs replacement, you distributor advance mechanism has become inoperative, the timing and the carb settings need adjustment.

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    Re: Cadillac 1969 quadrajet, bad idle

    By the way, did you check if your spark plugs are connected the right way from the distributor? If you switched a connection it means two or even four cilinders will not 'burn' and dump a rich mixture in your exhaust... That could also cause irratic idle and bangs.

    ...still can happen to the best of engineers.

    Oh, and don't use synthetic oil!

  15. #14
    3dfx is offline Cadillac Owners Member
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    Re: Cadillac 1969 quadrajet, bad idle

    By the way, did you check if your spark plugs are connected the right way from the distributor? If you switched a connection it means two or even four cilinders will not 'burn' and dump a rich mixture in your exhaust... That could also cause irratic idle and bangs.
    I have checked this many times and wires are correct.

    Oh, and don't use synthetic oil!
    I use 10W-40 mineral oil.

  16. #15
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    Re: Cadillac 1969 quadrajet, bad idle

    ^^I was just wondering, because oil wouldn't cause the banging in the exhaust...

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