2003 Deville poor acceleration, (video)
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1985-1992 Fleetwood, 1993 Sixty Special, All FWD Forum Discussion, 2003 Deville poor acceleration, (video) in Past Cadillac Vehicle Discussion; So this happened suddenly, started out just fine but after one stop it feels like power dropped in half and ...
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    Fleetwood70 is offline Cadillac Owners Fanatic
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    2003 Deville poor acceleration, (video)

    So this happened suddenly, started out just fine but after one stop it feels like power dropped in half and been like this all day. No codes. What could this be? Idles and cruises just fine, tried only up to 55 mph today, when trying to accelerate it really struggles, also will barely crawl when going uphill, slows down from 55 to 35 and that's almost flooring it. Both times in the video I floored it in Drive, at the end of the video you can see SES blinking but then it disappeared when I stopped, still no codes.
    https://www.youtube.com/watch?v=QA4yu4UH7j0

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    maeng9981's Avatar
    maeng9981 is offline Cadillac Owners Connoisseur
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    That seems like a clogged catalytic converter from looking at the video on my phone. Blinking SES light usually means that the car is experiencing a severe misfire conditions, which could possibly be contributed by a clogged CAT, or could've been the reason why your CAT is clogged.
    Fleetwood70 and Fleetwood70 like this.

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    Ranger's Avatar
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    Re: 2003 Deville poor acceleration, (video)

    Clogged CAT or a bad trans. I would expect some codes, but you can easily check (or have checked) the exhaust system back pressure to determine it the CAT is clogged.
    Fleetwood70 and Fleetwood70 like this.

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    Re: 2003 Deville poor acceleration, (video)

    Quote Originally Posted by Fleetwood70 View Post
    So this happened suddenly, started out just fine but after one stop it feels like power dropped in half and been like this all day. No codes. What could this be? Idles and cruises just fine, tried only up to 55 mph today, when trying to accelerate it really struggles, also will barely crawl when going uphill, slows down from 55 to 35 and that's almost flooring it. Both times in the video I floored it in Drive, at the end of the video you can see SES blinking but then it disappeared when I stopped, still no codes.
    https://www.youtube.com/watch?v=QA4yu4UH7j0
    ---------------------------------
    any time the SES light flashes - it is due to a misfire -
    and it will/should set the P0300 code -

    are you sure you are pulling the codes the correct way -
    press and hold the "OFF and "Info ^" buttons" at the same time -
    until the dash lights everything up -

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    Fleetwood70 is offline Cadillac Owners Fanatic
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    Re: 2003 Deville poor acceleration, (video)

    One code appeared P0410 secondary air injection system. No P0300 code but when checked with code reader it shows P0304 cyl 4 misfire detected.
    Can a CAT really clog up so fast? It ran like a champ just a day before.

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    Re: 2003 Deville poor acceleration, (video)

    The more I think about it, the less it seems like a clogged CAT. If that where the case, the engine would have a hard time revving. This seems more like a disconnect between the engine and trans.

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    MoistCabbage's Avatar
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    No, the speed is increasing in relation to the revs, it looks like a lack of power that gets worse as engine speed increases. If it's not the cat, I'd check fuel pressure next.

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    Re: 2003 Deville poor acceleration, (video)

    MC, look at the video again. Especially the last 5 seconds. Sure seems like the RPMs are increasing while the speed isn't. I don't think the relationship is correct at all.

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    The first time he revs it (and notice he starts off at ~10 MPH), RPM and speed increase together. The engine can't seem to do more than ~4,500 RPM, and the speed tops out ~35 MPH.

    I don't think what's happening at 20 seconds is slip, it's a downshift. The car is already going close to 35 MPH the second time, so when it downshifts, it revs (slowly, because of whatever the problem is) to ~4,000/4,500 rpm, and stays there.

    Also, the first time he revs it, it starts to miss at ~4,500 RPM, which makes me think it's leaning out.

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    Re: 2003 Deville poor acceleration, (video)

    No, I think the trans is OK. When I accelerate slowly it goes through all gears. The reason it tops out at 37 is because I was flooring it and the rpms wasn't close to redline to upshift, no power. And yes the second time I floored it downshifted to 1st. Basically it feels like parking brake is applied when I try to accelerate, + some misfiring.

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    Yeah, with no other P codes, and a lack of power, I'd check the fuel pressure.

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    Fleetwood70 is offline Cadillac Owners Fanatic
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    Re: 2003 Deville poor acceleration, (video)

    OK fuel pressure is about 35psi at idle and when I give it some gas it jumps to 45. Can't test it while driving.

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    Re: 2003 Deville poor acceleration, (video)

    35 is a tad low, but I don't think it is low enough to cause any problems.

    Seems to me it should drop slightly when you throttle up.

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    Fleetwood70 is offline Cadillac Owners Fanatic
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    Re: 2003 Deville poor acceleration, (video)

    One more thing I noticed, when cruising the Rpms occasionally drop for like less than a second, just enough to feel the stumble, about 50-100 Rpms when looking at the tach.
    Today i siphoned out the gas and filled with premium (just in case), and changed MAP sensor. But that didn't change anything.
    I'll unbolt and look inside the CAT sometime on the weekends, but I really doubt it is the problem.
    Any ideas on which sensors can go out without a code?

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    MoistCabbage's Avatar
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    None, they're all monitored.

    Sometimes CKP sensors fail without throwing a code at first, but that would cause completely different symptoms.

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