No Fuel to one cylinder
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The Classic Cadillac Forum Discussion, No Fuel to one cylinder in Past Cadillac Vehicle Discussion; Hello all, 1970 Coupe with a 472. This has me stumped. The driver side rear cylinder is not getting fuel. ...
  1. #1
    The Mole is offline Cadillac Owners Member
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    No Fuel to one cylinder

    Hello all,

    1970 Coupe with a 472.

    This has me stumped. The driver side rear cylinder is not getting fuel. I have run compression test and it's good. I have removed the valve cover and watched the rockers, intake and exhaust opening and closing. Pulled the wire and am
    getting spark. The plug is dry. the engine runs great with the exception of a cylinder not firing.

    The carb is pretty much shot, so was going to replace to see if that was the issue.

    I have never seen where one cylinder is not getting fuel.

    I have taken off the intake, there is no blockage. Gasket is not in the way, etc...

    If I do replace the carb, what is the recommended size of carb? I do like the Edelbrock series of
    carbs. (650,700,750)?

    Stumped.

    Any ideas.

    The Mole

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  3. #2
    chrisntam is offline Cadillac Owners Fanatic
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    Re: No Fuel to one cylinder

    My understanding is that the 472s got a 750 cfm carb and the 500s got an 800 cfm carb. I just rebuilt my 472 into a 500 and it was recommended to go back with a quadrajet. Don't exactly know why, other that easier hook up to existing parts and I went back with a factory manifold.

    Have you smelled the plug? Really no fuel? That's odd. The way the intake is made, fuel from each of the two primaries should go to 4 cylinders. Sorry, can't help any more on that.

    chris.

  4. #3
    Jaykeane is offline Cadillac Owners Member
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    Re: No Fuel to one cylinder

    700 would be my choice on an edelbrock.. both will work.. Your engine i don't think would flow any more than 600 CFM @ WOT..

    I'd guess that you have a vacuum leak of sorts, causing that cylinder to run leaner than the others. Are there any vacuum ports on the runner to the cylinder (like the brake booster)?

    vacuum leaks can cause the engine to 'skip' at low RPM.. and can be quite a nuisance

    John

  5. #4
    The Mole is offline Cadillac Owners Member
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    Re: No Fuel to one cylinder

    Yes I thought vacuum leak also, I even changed the intake gasket. No help. I will check the ports again. Good heads up though. I will keep chasing it though.

    Thanks again.

  6. #5
    aussiejohn is offline Cadillac Owners Member
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    Re: No Fuel to one cylinder

    Quote Originally Posted by The Mole View Post
    ,



    If I do replace the carb, what is the recommended size of carb? I do like the Edelbrock series of
    carbs. (650,700,750)?

    Stumped.

    Any ideas.

    The Mole
    Dear Mole,

    The Edelbrock carbs are, I believe, a re-design of the old Carter AFB that were and still are, far inferior to the Quadrajet. Don't let the shiny finish seduce you into purchasing one. Buy Cliff Ruggles' book on the Qjet, or find a good rebuilder such as Lars Grimsrud in Denver CO (V8FastCars.com) and put back the carb that GM designed the car to have.

    Regards from Down Under.

    aussiejohn
    the APEMAN and talismandave like this.

  7. #6
    Jeff R's Avatar
    Jeff R is offline Cadillac Owners Fanatic
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    Re: No Fuel to one cylinder

    Kind of odd as I would think if fuel is making its way around it would hit that cylinder too.
    Find where the intake valve is open and then blow shop air into the cylinder thru the plug hole. Not too much pressure at first as you don't want to blow crap back into the system.
    See where the air comes out. If you put your hand over the carb and you feel air or the 'hiss' sound changes then you don't have a major blockage. Also check the intake valve stem. Maybe there is a lot of leakage thru the valve stem allowing fuel to blow up into the valve cover area. Was that unusually clean in there when you took it off?
    And/or, crank the engine with the coil disconnected so it doesn't fire. Crank it enough to that all the plugs are wet and be sure that the back one is actually dry.
    Jeff

  8. #7
    The Mole is offline Cadillac Owners Member
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    Re: No Fuel to one cylinder

    Aussiejohn, will do. If I have to purchase a carb I will follow your advice as I do agree.
    Jeff, it was not clean around the rockers at all. I checked the intake when I changed the gasket. This is the weirdest thing .
    It isn't making a lot of since to me. The carb is like the last leg in the race.

    I really appreciate the input . more brains more ideas.

    Thanks The Mole.

  9. #8
    70eldo's Avatar
    70eldo is offline Cadillac Owners Connoisseur
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    Re: No Fuel to one cylinder

    I would replace the plug
    There is no way one cilinder does not get fuel, unless there is a severe blockage in the intake or valves.

  10. #9
    Mr. Sinister's Avatar
    Mr. Sinister is offline Cadillac Owners Member
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    Re: No Fuel to one cylinder

    If the engine is running great, you can't have a cylinder completely not firing. You would have a noticeable miss if the cylinder was truly doing nothing.
    A clean, dry plug is the sign of a healthy cylinder. Plugs should not be wet or black in a healthy engine. They should gradually turn grey or light brown over time, but will remain almost new looking for a good while when the air/fuel mixture is correct.
    If it were not getting adequate fuel, that's more than likely in the carb. If the carb can't atomize the fuel/air mixture properly, you'll get an imbalance in distribution to the cylinders. Some will run too fat, some will run too lean, but it's a VERY rare case when a cylinder gets nothing, and that's typically from a blockage. It will also be noticeably down on power. Since you did those checks, we know it's not that. If the plug was white, that's an indication of a overly lean condition.

    Here's a good chart on how to read plugs:
    http://gasolinegirls.files.wordpress...art.jpg?w=1440
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  11. #10
    sawyer is offline Cadillac Owners Member
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    First thing I'd do is a compression test on the cylinder that is missing.

  12. #11
    Jeff R's Avatar
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    Re: No Fuel to one cylinder

    Lets flip this around. Just not making sense to me so please allow me to ask the following questions--
    How do you know it is not getting fuel? How do you know a cylinder is missing and how are you determining which one it is?
    Jeff

  13. #12
    The Mole is offline Cadillac Owners Member
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    Re: No Fuel to one cylinder

    OK here goes. When I say its running great, I mean it starts , idles, etc. There is a miss though.
    I heard the miss and went old school. I pulled a plug wire one at a time until I discovered what cylinder it was. The wire would spark when held to the manifold. I then got a new plug put it in the plug wire and it sparked. Put the plug(new) in the engine and started it again. Still missed. Pulled the new plug and it was dry and still looked new. Compression test was all good. That was when I thought about the vacuum leak and pulled the intake. Checked the distributor, checked the intake for blockage. Nothing. The carb is due for a rebuild. Put a new intake gasket put it all back together and the same thing!!! So I figured the only thing left is fuel distribution. I have compression, I have spark, just no fuel.

    ----------

    Forgot to mention, turned the engine over with the valve cover off and watched the rockers to make sure the valves were opening and closing. All good.

  14. #13
    sawyer is offline Cadillac Owners Member
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    Try holding the plug wire away from the plug enough where the fire has to jump to the plug and see if it will fire on that cylinder then I have to do that anytime on old tractors the wire gets old and has too much resistance.

  15. #14
    carnut is offline Cadillac Owners Master
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    Re: No Fuel to one cylinder

    Swap wires in the cap. Does the miss move to another cylinder? If so, You have a faulty plug wire. Put #5 wire in #7 in the cap tower for instance. Also inspect the cap for carbon tracking. I dont believe you have a fuel problem.

  16. #15
    CaddyGas's Avatar
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    Re: No Fuel to one cylinder

    Check the spring weights in the distributor, are they loose, sloppy that can cause a miss also. Pull a weight slightly back does it spring back into place.
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