2001 Honda Civic HX with 238,000 miles on it. D17A6 Engine with VTEC. Manual transmission.
A few years ago, I noticed an "air-movement" noise but never really nailed it down or thought much of it, as I don't drive it frequently; this is my wife's car. Now I am noticing a few other things. I hear a horrible rattling noise when I get to anything over 2500 RPM. The more throttle I give it, the more distinct the rattle noise is. All heat shields are in tact and do not seem to be causing the rattle. I half-think a piece of the old front CAT that was replaced a couple years ago broke off and is now rattling in the rear CAT. I am also more recently noticing a "whirring" noise when I give it light throttle. "whhherrr-werrr-weeerrr-werrrrr-wooooo". It's hard to describe. The car also seems to have lost some power, but it's still driveable. Although the compression of the cylinders appears to be good. Honda only specifies a "minimum" of 135 psi, and I appear to have over 200. I'm not sure what "normal" is supposed to be. The front catalyst/manifold was replaced a couple years ago, due to cracks in the manifold creating an exhaust leak, and causing a P0420. The timing belt and tensioner were also replaced, and the crank/cam correlation matches known goods from the PICO database.
So I saved up for a pressure transducer (because I like cool tools), and started some experimentation. I put it in cylinder 3, and got a waveform during wide-open throttle cranking, at idle, and during a throttle snap. The throttle snap caught my attention, as during part of the exhaust stroke, it goes up to 6.5 PSI. But this isn't during the whole exhaust stroke, or even the average. Just a peak during the second half of the exhaust stroke. The John Thornton video suggests that a rise near the end might be a worn camshaft. I might need to watch that video again.
So then I took a few measurements with the pressure transducer in place of the front O2 sensor. At idle, the average pressure in the front cat is close to zero, while all the peaks are close to .5 PSI. At 3000 RPM, the pressure stays below 1 PSI. But during a throttle snap, there is a peak pressure of 3.4 PSI (more air allowed into cylinder). Being that it's a stick-shift, it's very difficult to obtain a brake-torque.
I don't do this for a living, so I am lacking practical experience to confidently interpret this, and am asking for assistance in interpreting these waveforms. As I don't want to throw $700 on a CAT without being sure (maybe it's a worn CAM?) Attached are all the pico captures described. Thanks for any help in solving this.
