I have been working on this car (92 firebird 305 tbi) for a couple of months and have fixed most of the problems but one keeps eluding me. It is running supper rich. Example today I put 5 gallons of gas in it bring the gauge up to about half a tank. Took two trips around the front yard so I drove it about 800 feet (low speed), and it sat at idle for about 20-30 min altogether. It is at just above 1/4 of a tank now. It was like this when I bought it. Since then it has had a new intake gasket, gasket kit on the TBI, fuel regulator, the timing has been set to 0 tdc, and about 4 sets of spark plugs as they carbon foul pretty quick, the tank is not leaking, and the gauge is pretty accurate.


With new plugs it has very little to no smoke coming out of the tail pipe as the plugs get more and more fouled the exhaust turns black at idle and smells of gas but clears up somewhat when the rpm’s get to around 2000. Above 2000 rpm the car has plenty of power even with carbon coated plugs. I have thought about the o2 sensor, tps, and coil but none of them seem like they should make it that rich or am I wrong. The injectors are spraying a good cone pattern and are no leaking, and the fuel return line seemed ok when I had the tbi off. I have had and intermittent code 33 but it only stays on for a couple of seconds and sometimes dose not come on at all. Am I missing something here? I have thought about hooking the return line up to compressed air to make sure it is clear but I’m not sure if that would do more harm than good. The car did sit full of gas for a couple years or so I am told.

 

Hey i have the same exact engine only in a camaro. I had that prob when its hella rich. I got MAP sensor readings and put a new one on and it cleared right up. At least for my car that was the prob. Hope it helps you.
Also check your EGR valve.

 

Thanks, I went out and disconnected the map sensor and started the car and no smoke. It seemed like it was missing a bit but the plugs are getting bad again, turned the car of and plugged it back in and the black smoke was back. So dose that mean the map is bad for sure or could it be that the manifold pressure is really off or there is a clogged vac line somewhere? i ahte to replace the map if it is not the problem as they are kinda expensive Thanks again for the help. At least now I know it’s not the fuel return……

 

Ok the map sensor has been replaced. The Intermittent code 33 has also been replaced with an Intermittent code 34. The car is still running rich not as rich but still pretty rich. The plugs are still fouling very fast, there is still black smoke out the tail pipes but not as much and the car is idling around 1500, but after revving it will drop down to around 500 try to stall then creep back up to 1500. It revs very quickly and freely in park but tend to bog in gear most of the time. At this point the car has a new map sensor, water pump, thermostat, cat back exhaust, tbi rebuild kit but original injectors, fuel pump, valve cover gaskets, most of the vac lines have been replaced, timing has been set, plugs, wires, fluids and filters have been changed. The car starts right up every time but runs like crap. I don’t think it is an internal mechanical issue because every once in a while it will run great for a few min no smoke and will leave rubber with no effort but if I turn it off the problem is right back when I restart the car if the problem dose not come back on its own after a min or two.

Thanks for the help every one i guess i will try replacing the injectors next. any ideas would be very appreciated.

 

Take it to a mechanic that has a Snap-On scanner. Look at what the BLM and INT readings are. These numbers will be determined by what the EGR sees. Your EGR may be taking a dump.