'88 TC very loud at 2500 RPM...

I'm trying to keep this thing on the road, 202K miles and runs great, but there is a very loud roar inside the car when the engine is at 2500 RPM. I can be driving 70 (about 2500 RPM), push in the clutch and the car gets quiet with just some minor rear end noise. With the clutch still in I can hold the engine at 2500 and it is loud again. I don't think this has anything to do with the drivetrain, just the engine. The engine runs great though. I'm sure what I am hearing is body resonance due to engine vibration, but why? The engine mounts don't seem soft or torn, maybe they are hard as rocks? Any ideas? I've checked the exhaust and it isn't touching anywhere. Anybody else solve this issue before?

Thanks,
Clay

How loud is it above 2500?

Hole in exhaust system. Leak/crack at the exhaust manifold or manifold/turbo or turbo/downturn area?.
Loose connection at the down pipe?

Does the engine move excessively when reved. Observe under the hood.

Is the lifting eye, mounted on the last exhaust manifold bolt swiveled around so it contacts the firewall?

I don't think there is an exhaust leak. I just passed the yearly emissions test. It sounds like it is coming from the rear half of the car. I'll look around for something contacting the firewall. I also need to listen outside the car while somebody else bring the RPM up...

Thanks

Oh, and it is loud enough that I have to turn the radio up to hear it...

Maybe it is exhaust though. I also get a CEL at idle that goes away as soon as I leave a traffic light. The code is 42. It has been doing this for the 3 years I have had it and it was doing it to the previous owner who changed everything he could think of and didn't get rid of it.

All the exhaust leaks I have had on other cars though were loudest under acceleration. This isn't.

Hmmm, I just went out looking for an exhaust leak and what I saw was on the passenger side engine mount there is a metal "tang" on the top of the rubber piece that sticks through a hole in the bracket that bolts to the subframe. It looks like there is metal to metal contact there. I am guessing it is due to a worn mount causing the tang to sit lower in the hole than it should. Here is a picture, but it is hard to see the contact. http://natomessageboard.com/uploads/0000...ount_1.jpg

Any thoughts are appreciated...

Thanks,
Clay

my car does the same thing... if i shove about 4 or 5 rags in one the tail pipes it will go away....
i just ordered my 3in exhuast from stinger and hopefully this will be last week dealing with it as it has been there since i made the exhaust in 2004

Sounds like a resonance causing the exhaust to rattle against the chassis to me. I've seen it plenty of times and it's crazy how loud it gets inside the car.

BJL, are you putting the rags INSIDE one tailpipe? I have noticed that the exhaust hangers are starting to crack, but I went over the system last weekend looking for a place it could touch and it all seemed pretty good. I have engine mounts on order. Once they are swapped I'll go from there. By the way, that picture I posted is upside down...

FYI, the code 42 at idle is either 1) fuel pressure too high, or leaking FPR diaphram 2) TPS voltage too high, 3) VAF idle voltage too high. If it is this, the idle bypass (this is NOT the spring tension adjustment) on the VAF can be adjusted to bring the idle VAF voltage down.

Thanks Jeff, I'll double check those things. The CEL happens more often when it is cold out, ie. it rarely happens in the summer and happens at every traffic light in the winter. Does one of those issues stand out based on ambient temperature?

Actually, as I sit here and think about it, my last 2 emissions tests showed barely passing numbers at idle. I guess a leaking FPR diaphram would allow fuel into the vacuum/intake without being metered but may not affect the pressure. I'll double check the TPS and VAF voltages and then look at replacing the FPR.