fastcgi-mono-server4 and nginx not working

Question

I'm trying to get Mono working with nginx using fastcgi-mono-server4. nginx and fastcgi-mono-server4 are apparently in communication (I can get that far using both a unix and a tcp socket), but once fastcgi-mono-server4 logs getting an incoming request (when I hit the nginx listen url with my browser), nothing happens and nginx times out with a 504 Gateway Time-out after a bit. Here's the log from the fastcgi-mono-server4 process (I'm running everything as root, including the nginx workers processes, to rule out permissions problems):

$ sudo MONO_OPTIONS="--debug" MONO_IOMAP=all fastcgi-mono-server4 /printlog=True /applications=/test:/home/friis/code/TestingMono/TestingMono/ /socket=tcp:127.0.0.1:9000 /loglevels=Debug
[2013-07-31 21:33:15Z] Debug   fastcgi-mono-server4
[2013-07-31 21:33:15Z] Debug   Listening on port: 127.0.0.1
[2013-07-31 21:33:15Z] Debug   Listening on address: 9000
[2013-07-31 21:33:15Z] Debug   Root directory: /home/friism/code/TestingMono/TestingMono
[2013-07-31 21:33:15Z] Debug   Max connections: 1024
[2013-07-31 21:33:15Z] Debug   Max requests: 1024
[2013-07-31 21:33:15Z] Debug   Multiplex connections: False
[2013-07-31 21:33:54Z] Debug   Accepting an incoming connection.
[2013-07-31 21:33:54Z] Notice  Beginning to receive records on connection.
[2013-07-31 21:33:54Z] Debug   Record received. (Type: BeginRequest, ID: 1, Length: 8)

The TestingMono directory holds an ASP.NET application that serves just fine using xsp4.

Any suggestions for debugging this problem?

Versions:

$ mono --version
Mono JIT compiler version 3.0.12 (master/d6c5db8 Sat Jun 15 20:13:22 PDT 2013)
$ fastcgi-mono-server4 --version
fastcgi-mono-server4.exe 3.0.0.0

---

UPDATE

nginx config:

server { 
         listen 8080;
         server_name localhost;
         access_log   /var/log/nginx/your.domain1.xyz.access.log;

         location / {
                 fastcgi_pass 127.0.0.1:9000;
                 # fastcgi_pass unix:/tmp/nginx.socket;
                 include /etc/nginx/fastcgi_params;
         }
}