307 runs bad
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5.0 and 5.7 Discussion, 307 runs bad in Cadillac Engine Technical Discussion; This is my mothers' finace's '87 Brougham.... the car has a brand new long block with about 10k miles on ...
  1. #1
    Night Wolf's Avatar
    Night Wolf is offline Cadillac Owners 10000+ Posts
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    307 runs bad

    This is my mothers' finace's '87 Brougham....

    the car has a brand new long block with about 10k miles on it.

    it has a brand new oem style carburator

    it has a brand new complete exhaust system

    full tune up

    Heres the deal, it idles rough, it shakes the car quite a bit for a 307 (which is normally really smooth) and at the tail pipe, it definitly sounds like a miss and just not running right. When you hit the gas, there is a low spot, and there is no power at all... I mean, we were pulling out, and he was like look, this is to the floor, I was like what? I mean, it was bad. Also, the car will only reach about 65mph on the highway.... and it gets horrible gas mileage, like 10-12mpg.

    I figured the new carb is bad, but it was doing this with the old carb (which was replaced when he got the car... 8 years ago) hence the reason for the new carb.

    The plugs/ wires were new with the engine, and look good, a month ago we replaced the cap and rotor which looked worn.

    What could the problem be? We were thinking the cat on the new exhaust may be bad, so we were going to remove it.... but I dunno, its new, and I don't think a cat would cause as much of a power loss as this. I mean, when my cat was smashed up and rattling inside, it wasn't anywhere near a power loss like this...

    We adjusted the only asjustments on the carb... or so it appeared, the idle mixture... and it did smooth out the idle a bit... but still.

    They are driving down this weekend, and I'd like to maybe try to get the problem fixed this weekend.

    Could it be a timing issue? would that cause all the above mentioned stuff? we haven't checked the timing yet.

    The new engine was put in, in NY, then drove to FL, then up to NY then back to FL with this problem.... the last trip coming down to FL he was towing his trailer and said there was just no power at all.

    Anyone have a clue?

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  3. #2
    Night Wolf's Avatar
    Night Wolf is offline Cadillac Owners 10000+ Posts
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    Re: 307 runs bad

    Anyone?

    We are gonna check the timing tomorrow... hope that helps it...

  4. #3
    Night Wolf's Avatar
    Night Wolf is offline Cadillac Owners 10000+ Posts
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    Re: 307 runs bad

    heh, it was all the timing.

    Whent he new engine was put in, the guys set it to 20* but without grounding out the computer for spark advance

    it was 6-8* retarded.

    So we brought it to 24ish, and it runs great.... solved every issue.

  5. #4
    N0DIH's Avatar
    N0DIH is offline Cadillac Owners Master
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    Re: 307 runs bad

    Cool, sorry, I missed the thread!

    Common problem, easy to do.

  6. #5
    boatman is offline Cadillac Owners Member
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    Re: 307 runs bad

    If all else has failed so far, I would replace the plugs, could have a hairline crack in one of them.

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