Under body damage

[pyro_104]

Earlier this year I hit a rock on the road about the size of two fists put together. It's not a pretty story, but basically it was in the middle of my lane, it was a steep down hill with a single lane each way, no space on the side of the road and the rock was just around a fairly blind corner. It was either hit the rock, brake very heavily and get rear ended or go head on into another car. Not too hard a decision, so I went over it, aiming to get it inside my wheels, but not centered (so as to avoid the diff). The bang was very nasty and brought a tear to my eye, closely followed by some curses at the many quarry trucks in our area who no doubtedly dropped the rock.

Anyway the sum of it is that it's severely dented one side of my extractors (just before the two banks join) as can be seen in the attached image. I guess my question is, how badly do you think this new exhaust restriction is affecting my car? It seems to be running ok, however my O2 sensor is dying (coincidently just downstream of the dent in the photo), the idle is a bit rough but then it always has been. I rarely flog my car so it's hard for me to say whether there's a difference in top-end performance.

[pyro_104]

On a related matter, since the incident I've noticed that when I'm in reverse (but no throttle applied) I get a rattling from the rear of the car. Any idea's what this may be? I'm thinking maybe the rock hit my exhaust (snapped a mount) or cat (shattered the honeycomb), or even diff, but I don't get this rattling unless in reverse. It sounds/feels too far back in the car to be gearbox related. It's hard to pin down where the noise it coming from. Maybe I need to get a friend to reverse while I listen from outside. It is only really noticable when there's no throttle applied.

[Mk III the HSV]

That rock certainly made mess of your extractors. I would have a look around at the wreckers to find a replacement. Although I would say it's still very driveable, but is probably costing ya in performance and fuel economy.

[chosen_one]

On a related matter, since the incident I've noticed that when I'm in reverse (but no throttle applied) I get a rattling from the rear of the car. Any idea's what this may be? I'm thinking maybe the rock hit my exhaust (snapped a mount) or cat (shattered the honeycomb), or even diff, but I don't get this rattling unless in reverse. It sounds/feels too far back in the car to be gearbox related. It's hard to pin down where the noise it coming from. Maybe I need to get a friend to reverse while I listen from outside. It is only really noticable when there's no throttle applied.

I get this rattle too (both in reverse and when in drive when moving without applying throttle, eg in a carpark but not on the raod when at speed). It comes and goes and coincides with when I get new rubbers put on the back of the exhaust system. I put it down to metal on metal somewhere and as the rubbers age and stretch it goes away. Maybe when you hit the rock your exhaust system moved a bit, you know from that central rubber clamp near the cat. I'm sure someone on here will know.

[Scooter79]

I dented my exhaust a few years back just behind the cat. Was only a subtle dent but made a big difference to the performance (caused acceleration problems). A dent like yours surely must be causing some serious back pressure build up. Took it too a muffler guy and he fixed it in 20 minutes with an oxy torch. He was able to heat it up and reshape it without taking it off. Genius! Only charged me $30 for his time.

[pyro_104]

Hmm unfortuantly I doubt mine is going to be a $30 quick fix =(

[matt69]

ouch dude. just take her round and get sum quotes. could also try the wreckers and go second hand.

[Patrio7]

ouchie bang :'( thats a nasty hit, did your car think it was a rollerblade or something?