This forum has helped me loads in the past, but I guess it's time to throw a question of my own in the mix. Thanks in advance for trudging through my long post.

Yesterday my generally well-behaved automatic '89 740 Turbo wagon suddenly started running loud while I was driving in third gear at about 60 kph (40 mph). I would call it 'excessive exhaust sound'. From inside it sounds like it is coming from above the transmission or in front of the firewall, but from outside it is most audible at the tailpipe as a sort of 'lubbing' sound, not a leak but more like the system is plugged up. It doesn't really sound abnormal in the engine compartment, but from inside the car it sounds pretty loud (which strikes me as unusual). Not surprisingly, it is the loudest when the car is working hard, e.g. accelerating or driving uphill. Just cruising at a low RPM it doesn't sound that bad.

Today I jacked it up and checked out the whole exhaust system, but there is no physical damage and no audible leaks, just some minor streaking around the joint aft of the catalytic converter. I pulled the cat thinking it was bunged up with deposits, but it looks surprisingly clean and white. The pipes on either side just have a bit of soot, nothing out of the ordinary. It feels like there's still plenty of flow out the pipe as well. When I put it back together it seemed to sound normal for a two-minute drive, but upon restarting the engine the noise returned (of course, eh?).

The only other detail I can really give is that the car runs pretty well normal (RPM, idle, etc), except it feels a bit 'loose', if that makes any sense. I also feel like I can hear the turbo winding up louder than before.

Could the gasket at the manifold be shot? Though it looks fine, I guess I will pull that next. I thought I'd get an opinion on the forum first, especially since I live in an old motorhome in the parking lot of my workplace, so I can only work on the car after about 8 pm (hence the post-midnight-post!).

Any thoughts on the exhaust system or suggestions for an entirely new area for investigation would be much appreciated.

Cheers,
Tristan

 

Okay, drove it a bit more this morning -- to get the windshield replaced. When it rains, it pours, eh?

It is loud from inside when turning over, accelerating from a stop and driving uphill. I am wondering if there's a chance it isn't the exhaust at all, but rather motor mounts or something of the sort causing extra vibration in the engine compartment.

I would appreciate any suggestions you all might have.

 

Why is there any streaking around the cat? Motor/ tranny mounts could be suspect and easy to check. It would explain both the loose feel and the fact the noise went away after you tightened up the cat, then when the drive train torqued, it stressed the joint and creates a small leak again,

Just a guess,