Date: Mon, 8 May 2000 12:35:32 -0700
From: "Ulen, Robert S" (Robert.Ulen@PSS.Boeing.com)
Subject: (rx7)  Exhaust Leak Findings - Lessons Learned
I though I would share my trouble-shooting results for those of you may one day detect what sounds like a slight exhaust leak on your FD. This write-up could save you some time, and point you in the right direction.
But first, I must pass on my axiom which applies to trouble-shooting this car sometimes:
- ------------------------------------ "Complex problems have simple, easy to understand wrong answers." - ------------------------------------
Based on the responses I got from the List, this problem seems very rare, and the symptoms may vary depending on how bad the failure is.
A LITTLE BACKGROUND
After driving hard one day, I popped the hood in my garage (quiet background) while the engine was running, and instantly notice what sounded like a slight exhaust leak near the turbos. After studying up on all the possible things that could cause an exhaust leak, and some advice from the List (thanks to all who gave me some advice), I started a long, and careful trouble-shooting plan which paid off in the long run.
I determined that there are many possible sources for an exhaust leak on an FD, namely:
The following match with the numbers above:
So, it means I must remove the extension manifold to repair this. No biggie, it will give me an excuse to do the silicone hose/tie wrap job too.
From: Steve Cirian (steve@ScuderiaCiriani.com)
My car was making a hissing noise that sounded like it was coming from the exhaust in roughly the transmission area. It turned out to be a bad gasket for the airpump hose going into the main cat. There is also a short piece of rubber hose in that area that could split or come off (not that poppoing off is very likely given the clamps on it).
The pre-cat can become clogged. This shows up as poor idle and/or boost problems, and the pre-cat will sometimes even glow red after extended idle. (Note that it is common for the pre-cat and even downpipe to glow after hard driving.) --Steve
Date: Tue, 30 Jan 2001 23:34:53 EST
>exhaust overheat light is on
The exhaust system overheat indicator is a simple sensor that is a thermister. That is to say that it is a resistor that changes its resistive value as it is heated or cooled. The circuit is an op-amp voltage comparator that has a window value built in that will activate when the thermistor reaches a certain value based on heat. The circuit must sense some resistive value all the time or it will activate.
It is reasonable to assume that somehow your sensor(thermistor) has come disconnected from it's cable going to the comparator portion of the circuit. The sensor is under the carpet over the catalytic converter. It requires a bit of work to get to. However there are places where various harnesses plug into each other more accessible.
If you are looking for exhaust smoke information/troubleshooting, see the engine smoking troubleshooting page.