i have an 87 firebird 355,5-speed,tuned port mass air. the problem i have been having is for the last couple months evertime my car reaches 160 on the temp gauge are hotter the chugs only at part throttle when i let off or romp on it quits. and there has also been a couple time recently when i first start my car the check engine light comes on and it tries to die and start smoking really bad. also the other night when i was driving home i went to stop at a stop sign and the idle went down 3-400 rpms and started chugging. then i stop at the next stop sign and did it again but worse it start pouring out black smoke from everywhere and all i could smell was a lot of gas like it was running really rich. I tried to hookup 2 different code scanners and they both said system not responding then i tried to do the in car one and it would ever quit flashing code 12 it would never finish. so if anyone has any ideas are knows how i could test each sensor let me know. oh and by the way the motor has 8,000 miles all new igniton plugs,wires,coil,cap&rotor etc.

 

Well, flashing 12 is a good thing. At least you know your computer is good. I'd take a good look at the fuel pressure or possible the FPR. Black smoke is a good indication of a rich condition so if nothing else, you've got it narrowed. Someone else told me it could indicate timming problems as well.

 

wouldnt it be a problem if the computer never quit flashing code 12 it never has trouble codes or a finish. The fuel pressure regulator is less than a year old it is a bbk adjustable regulator and when it was doing the black smoke all u could smell was gas.
it acted like it was running the normal amount of fuel but retarded the hell out of the timing and it did in a matter of a second. the next day i went out and drove while the motor was cold and ran fine it only does it after 160 degrees

 

355,

I'm taking this analysis a step at a time.

First, your ECM - The heart of the entire system. If you jumper the ALDL to invoke Diagnostic Mode, you should always get a '12'. It will flash the '12' three times, then flash all other stored error codes, again three times each, in numerical sequence (not necessarily the order of storage nor importance). When all other codes have been strobed out, the ECM will flash the '12' three times, then repeat the cycle endlessly until the jumper is removed or the ignition is turned off. If all you are reading is an endless string of '12' the ECM has no stored error codes. That doesn't help you diagnose the problem much, but does indicate that the major engine sensors and systems are at least functioning within acceptable parameters.

Second, the temperature indication. There are a few significant steps in the engine coolant temperature that enable different operational modes of the ECM. Given that the factory temperature gauges are not laboratory accurate in calibration, and that the gauge sensor is in a separate location from the CTS that reports to the ECM, the actual temperature that the ECM is reading may not be exactly the same as what the gauge is displaying. Still, the information can be helpful.

Here are some of the major CTS-related parameters for your ECM:

Coolant Temperature Sensor Related Parameters

Cold spark advance disabled above 56°C (133°F)
EGR Duty-cycle enabled at 56°C (133°F)
Highway Mode spark advance > 59.8°C (140°F)
Knock Control enabled > 67°C (153°F)
Diagnostic communication enabled at 70°C (157°F)
Code 13 (oxygen sensor fault) enabled above 70°C (157°F)
EVAP canister purge enabled above 70.3°C (158.5°F)
Hot closed-loop timer enabled above 70.3°C (158.5°F)
Target IAC idle RPM >80°C (176°F)
EGR Duty-cycle at MAX >80°C (176°F)
Cooling fan duty cycle at 100% at 80°C (176°F)
Acceleration enrichment multiplier at 1.00 below 80° C (176°F)
Acceleration enrichment multiplier at 0.75 above 80° C (176°F)
Acceleration enrichment decay factor at 25% below 80° C (176°F)
Acceleration enrichment decay factor at 40% above 80° C (176°F)
Fuel limiting factor timer at 217 counts below 80° C (176°F)
Fuel limiting factor timer at 169 counts above 80° C (176°F)


As you can see, there are several key events that occur around the 160°F (71°C) range:

The knock sensor and knock control system become active at 67°C (153°F). If your system is detecting excessive knock, timing could be severely retarded and yet no error code would necessarily be set. What is your base timing?

The EVAP canister purge control solenoid is enabled above 70.3°C (158.5°F). If you have a fully saturated EVAP canister, the system could be admitting raw liquid fuel via the purge line, and no error code would necessarily be set. That would definitely cause your symptoms. You could temporarily remove and cap the purge line as a test of this theory.

The EGR would also be active in this temperature range, and any EGR operation or leakage through the EGR valve would only compound a rich mixture/incomplete combustion problem.

Your ECM can achieve closed loop operation at 70.3°C (158.5°F), and if the oxygen sensor signal is weak (but still within the acceptable range of operation) the ECM would attempt to enrich the mixture to compensate, and not necessarily set an error code. This is a common failure more of an oxygen sensor.

I'd suggest verifying the operation of the O² sensor first. If it's more than 30,000 miles old, or has possibly been contaminated with a non-sensor safe sealant, coolant, or some other foreign substance, it may not be providing a reliable signal and should be replaced.

Once that's established, you should test the EVAP canister purge control and inspect the canister for accumulations of raw, liquid fuel. Frequent short trips and rapid temperature cycling of the fuel tank can saturate the canister. On cold days, your hot exhaust system can warm the fuel tank, purge lots of vapors from the tank, then cold outdoor air will drop the pressure quickly once the engine is off. The short trips compound this problem by not allowing adequate time for the canister to purge thoroughly. As mentioned, you could temporarily disable the system to eliminate the possibility.

Finally, the ignition timing advance and base timing should be checked. Try the factory specs at first, and test the EST and knock sensor operation.

You may in fact have a combination of these problems, so I'd strongly suggest a complete check of all the possibilities, even if one of the items is apparently the cause and makes the situation improve somewhat.

Good luck.