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Thread: Failed the dollar bill test

  1. #1
    man1ey's Avatar
    man1ey is offline Cadillac Owners Member
    Automobile(s): 1968 Deville Convertible
    Join Date
    Aug 2005
    Posts
    21

    Question Failed the dollar bill test

    As if "failed the dollar bill test" doesn't say it all, tell me if you guys agree with the diagnosis:

    Problem: rough intermittent idle, doesn't seem to be tied to one cylinder. Idle wobbles around by about 50 rpm but there's no pattern to it, backfires softly through exhaust with a lot of throttle or when coasting downhill, strong unburned gas odor.

    1968 472, 59k original miles, stock except for dual exhaust and MSD 5 ignition I inherited with the car. (Original ignition cannot be restored - I spent a week trying and it's not happy).

    New in last week: reman distributor, cap, rotor, points, wires, plugs, coil, reman Q-jet, fuel pump, fuel filter.

    Timing 5 deg at 550 w/ transmission in drive, vacuum advance plugged. Dwell dead-on 30 deg but apparently it doesn't matter per MSD tech support - points just act as a low-voltage trigger for the MSD box and box controls dwell.

    A vacuum gauge on the intake flutters rapidly over a range of 1.5 in Hg. No matter where the throttle is, it's always fluttering. It also fluctuates slowly at idle between about 15 and 20 in Hg, fluttering the whole time.

    Plugs look good on all cylinders, tan insulator, not wet, not sooty. Then again, I put about 30 highway miles on it just before I pulled them so it could have burned off something.

    Compression test with all plugs out:
    PASSENGER
    1 160
    3 134
    5 149
    7 162

    DRIVER
    2 156
    4 154
    6 156
    8 145

    Fails the dollar bill to the tailpipe test on the pass side - sucks the bill up about once per second or so. On the driver's side no suction. That makes me think it's valves on the pass side as opposed to slack timing chain, but starter has a tough time the first few revs even with timing correctly set, so I'm wondering if chain isn't slack or jumped too.

    I'm about to pull the heads and send them off, but would you guys try anything else first?

    Thanks,
    Mike

    Last edited by man1ey; 03-13-06 at 07:30 AM.

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  3. #2
    Join Date
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    Re: Failed the dollar bill test

    I would think a tight valve guide or weak valve spring might cause your problem. Have you installed a vacuum gauge on it yet? Does the guage fluctuate?

  4. #3
    man1ey's Avatar
    man1ey is offline Cadillac Owners Member
    Automobile(s): 1968 Deville Convertible
    Join Date
    Aug 2005
    Posts
    21

    Re: Failed the dollar bill test

    Katshot, thanks for reminding me. I did try this a couple of weeks ago and forgot about the result.

    A vacuum gauge on the intake flutters rapidly over a range of 1.5 in Hg. No matter where the throttle is, it's always fluttering. It also fluctuates slowly at idle between about 15 and 20 in Hg, fluttering the whole time. What do you think?

    Mike
    Last edited by man1ey; 03-13-06 at 08:57 AM.

  5. #4
    Join Date
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    Re: Failed the dollar bill test

    I'd suggest that a valve job would most likely cure your ills.


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