Running Poorly

I have a 91' Infiniti Q45. Lately my car has been running poorly. Here are the symptoms:

1) Rough idle

2) Black Smoke coming from the exhaust

3) I noticed a hard to describe odor coming from underneath the car, smells like exhaust (catalytic converter?)

4) Poor fuel mileage

5) Lacks power.

I ran diagnostics using the onboard computer and it flashed a 34 code which the book says points to the "Detonation Circuit". Based on what the technical manual says, there are a few most likely culprits:

A) Fuel injectors
B) Spark Plugs
C) Fuel Pump
D) EGR Valve

Does anyone have any ideas?

I have a 91' Infiniti Q45. Lately my car has been running poorly. Here are the symptoms:
1) Rough idle
2) Black Smoke coming from the exhaust
3) I noticed a hard to describe odor coming from underneath the car, smells like exhaust (catalytic converter?)
4) Poor fuel mileage
5) Lacks power.
I ran diagnostics using the onboard computer and it flashed a 34 code which the book says points to the "Detonation Circuit". Based on what the technical manual says, there are a few most likely culprits:
A) Fuel injectors
B) Spark Plugs
C) Fuel Pump
D) EGR Valve
Does anyone have any ideas?

First off, you are not in the right area to receive the best help. While I30/I35 and Maxima's are close cousins, the Q uses an engine that is not shared with any car car in the Nissan/Infiniti lineup-especially the '91. You have a 4.5L 266hp V8 while a 91 Max would have a 3.0L 160hp V6.
However, if you follow the list of items that are under normal 120K mile check-up and replace them, you most likely will correct at least some of the problem. The items you have listed are usually checked at 60K/120Kmiles. Items to replace would be PCV valve, belt(s), fuel filter, sparks plugs, air filters, and hoses. That just the basics. Actually, the 120K maintenance on a Q is quite lengthy and runs just under a grand at the dealership. You can find a check list elsewhere on the net.