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2003 Deville poor acceleration, (video)

22K views 27 replies 8 participants last post by  cadillac_al2 
#1 ·
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
 
#4 ·
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 -
 
#9 ·
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.
 
#10 ·
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.
 
#14 ·
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?
 
#24 ·
It's a ceramic honeycomb. Looks muck like the aluminum diffuser in a MAF, but longer.

Clogging is easier to diagnose with the cat removed, so you can shine light through it, but the cat is welded to the rest of the system on the OPs car, so cutting welding would be required to check it "correctly".
 
#25 ·
Clogging is easier to diagnose with the cat removed, so you can shine light through it, but the cat is welded to the rest of the system on the OPs car, so cutting welding would be required to check it "correctly".
Yes, it was the cat. I cut it off today and when I shook it, the front honeycomb was rattling inside, the insulating mat around it was broken down and all the trash clogged the rear one, I could barely see any light through it. I had my brother weld a piece of pipe in place of CAT and the car now runs like never before.
Thanks everyone.
 
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