I was hopeful that someone might have some thoughts on what might be the issue with this '04 Civic.

The engine is making a strange "brrrrrrruuummmmp" noise.

It happens only when the engine is decelerating, not accelerating. It's quite loud, but relatively short.

It does not occur at steady idle, at start-up, or even with the engine at a constant higher-than-idle rev. Just when you take you foot off the gas, from a position of higher-than-idle revs.

Here is a short video. Rev up at 9-10 seconds into the video, noises at 10-12 seconds, again at 20, and again at 29, after longer period of high revs.

I'm completely stumped.

link to vid:

BillsCarSounds004_x264.mp4 video by RDJESQ - Photobucket

 

Damn.. it's bad engine, how many miles and when is the last time you change the oil and did you see any metal sparkling shaving came out??

My guess is piston and/or rod, anyone else want to chime in??

 

It does sound like a piston or rod hitting something. My friends 240sx was doing something similar and he said the PO has torqued the valve cover down too much and a valve was hitting it. May be plausible.

 

Thanks for your comments.

Here's more info, if it helps.

The car has been very well maintained.

We're just passing 190K miles, but those have almost all been highway miles (it's a commuter car), not hard stop-and-go.

In fact, the car was running so well at 185K, we re-upped the investment in it, hoping for another 100K out of it, possibly: new tires, new sparkers, changed one of the oxygen sensors.

I do my own oil, so I get control over the type and filter. The oil was just changed, less than 1K ago, but, that said, the oil did seem a bit low when I checked after this problem. Very odd, that happening, as well. As I monitored from cold idle to warm, I noted a little bit of knock that I've never heard before, but it was gone in less than a minute and did not repeat...

I thought about piston/rod, but wouldn't those be a problem at acceleration, too?

 

When you changed the oil did you have any metal shavings in it. If it was the piston i would think it would do it all the time. But it happens when you let off it is weird. Have you tried to pin point where the noise is coming from?

 

I didn't notice any metal shavings, but I was in a big hurry. Actually, I still have the oil, because I transfer it from the pan back to the plastic container it is sold in, for recycling. The container is still in the trunk, because I haven't remembered to stop and sign it away at the recycle counter.

I haven't tried to pinpoint the sound. I don't know where the throttle control is under the hood on the Civic, partly because it's been maintenance-free, in serious respects, and it is hard to press the gas peddle and also listen under the hood! (On the other car, I know right where the throttle body is.)

 

I think it's a drive by wire system, the only at home way to rev it up is to have a helper press the gas pedal. Try to localize the noise, it might be just a heat shield or something. If it seems to be on the side of the engine, you could also take the external belts off so the accessories don't turn.

 

Just a follow-up:

Local shop says part of catalytic converter's honeycomb may have broken off and is rattling around in there.

From what I'm learning, replacing the cat on this car is a magilla, because Honda integrated it with the exhaust manifold...yikes!

 

Just a follow-up:

Local shop says part of catalytic converter's honeycomb may have broken off and is rattling around in there.

From what I'm learning, replacing the cat on this car is a magilla, because Honda integrated it with the exhaust manifold...yikes!

 

(oh, no engine code light, with this, which is weird, if it is the cat)