Well it seems I bought a lemon.Yesterday I took it out the muffler shop with a new magnaflow cat and on the way to work the service engine light came on I drove home thinking its just a sensor or the gas cap but the *** car wouldnt start up AGAIN!It started but immediatly shut off I tried to start it and it sounded like it wanted to but after a few tries it just started clicking.The guy who replaced the catylic converter said their is two of them and he can only replace the one he did,he also mentioned to check the 02 sensor.?????????????  

my mechanic says Its the electronic module and a cam sensor and something about the car being shot?does this sound right?  

This kinda ended up where I thought it would as I couldn’t see where the catalytic converters contributed to the problem. That’s not to say they don’t need replacing, but they’re a problem not related to the inability to keep the engine running. You really need a sharp guy to read out the failure codes from the computer and put that information together to form a picture of what’s going on. It can be difficult to separate cause codes from affected codes. That’s to say when something significant fails, its failure cascades thru other components causing them to throw a code. Often these are software glitches caused by the original failure, but this is what a good diagnostics guy gets paid to figure out. You’ll pardon me but your “mechanic” sounds like he’s in over his head with these high tech systems. You’ll find that throwing parts at it will become more expensive than a factory trained technician doing diagnostics. The failure you’re experiencing can have many causes, doing diagnostics without the computer codes is very difficult. Failure of the O2 sensor and the converters, while these will set a code, none will result in the failure mode you’re getting. One can reduce this to fuel problem and or ignition. The issue is what in those systems is the cause.  The fuel system could be a lack of pressure, this could be a plugged filter, failing pump, dying pressure regulator, a sensor, a bad connector or wire. The ignition could be most anything in the Opti-spark system. Chevrolet went thru a number of upgrades on this thing to overcome problems. By the time they got to the LT-4 things were pretty stable but it still is a rather sensitive system. Dirt and water (condensation) getting inside the system mess it up pretty good. Bad connectors or wires are always a problem as are a host of engine sensors. A failure in the throttle position sensor will provide incorrect information to the computer same goes for the several engine temp sensors that furnish data to the computer. The manifold absolute pressure sensor would be another that could send false information to the computer. Again any of the wiring or connectors in the circuit can become a problem. The vehicle speed sensor is another possibility, if this gets out of synch with what gear the computer thinks the car is in or any of the engine sensors, the computer can’t provide the proper fuel and timing curves.  

Going with what Bogie said, seems like it might be time for you to take the car to a good Chevy dealership for some diagnostic work.  

I took the car to get a computer diagnostic this morning.I got a couple codes:P0420 and bank 1.The mechanic said its the oxygen sensor and the catalystic converter he said its a common problem with Camaros and Thunderbirds?I had one Cat replaced so he told me I should of replaced the pair.I asked what would cause the break down I was told it was bad maintenance?  

What you're experiencing is a good example of why you have to be careful when buying a used performance car. Usually cars like yours are "driven hard and put up wet" as the saying goes. The issue with the cats might be from someone running some leaded fuel in the car, which will toast the pellets in a catalytic converter. O2 sensors wear out over time anyway, and with a car that's seeing a lot of WOT use will wear out an O2 sensor even faster.

The good thing is, it can always be fixed!  

Is this the only info coming out of the reader?

I'll look these up and go thru the systems configuration and get back to you.

I'm still not convinced that cats or O2 sensors are the root problem. At worst, plugged cats and crappy O2 sensor info should throw the computer into open loop, limp home, which is a mode from which it's often hard to tell there's a problem other than you have a "Check Engine Soon" light.

To go with what 55 Guy has to say, cats and O2 sensors don't last forever. Especially when the car is driven hard, these things get really hot and the cats get fried pretty quickly when the mixture is forced into a rich mode for more performance. This goes back to your resistor question which presents the next question, was there a resistor in the engine temp sensor circuit to the computer? This would force the computer to throw extra fuel at the engine all the time.

But even with that as an excuse the converters and O2 sensors are pretty shot by 50-60 thousand miles. I had watched the annual emissions check indicate the exhaust was getting dirtier on my Franken Mouse powered S-15. This year I put a new exhaust on it with dual converters and new O2 sensors and the emissions came way, way down.

Bogie  

OK I took your P0420 code and went thru the circuit lay out thinking of the symptoms that you’ve related to us.

P0420 on the surface is the Bank 1 O2 sensor, but looking at your car’s failure mode it’s clear that this fault code is not caused exclusively by the O2 sensor. So what else is on that circuit? Wow, lots of stuff! That which is directly associated with that circuit and could contribute to the fault code are the following:

- Hot Engine Run Fan Actuator, This controls the electric cooling fans when the engine is in “Run” mode and is overheating. Probably not contributing to your failure.

- Hot Engine AIR Pump Relay; This injects, or not, air into the exhaust manifolds to burn excess hydrocarbons to water and CO2, it also converts CO to CO2. A failure here will blow a SMOG test and could cause the O2 sensor and catalytic converter to overheat. I’d give this a “maybe” it doesn’t really fit the failure mode but issues with this could contribute to catalytic converter and O2 sensor problems from overheating them.


- EGR Solenoid; A failure here would cause the engine to run odd if exhaust gases were introduced at the wrong time, while making the engine herky-jerky and will fail a SMOG test, it wouldn’t cause the engine not to run. I give it a "low maybe".

- Canister Purge Relay; This is where the vapors from the fuel tank accumulate when the engine isn’t running. The relay opens a valve to vent the canister’s contents into the intake for a short period of time when-ever the engine is started. A failure here would probably be unnoticed. However, if the fuel tank failed to vent as fuel was consumed it would eventually develop a vacuum that the fuel pump couldn’t overcome and it would cease delivering fuel to the injectors. The car would simply stop running till a pressure balance was restored in the fuel tank. This is a sort-of maybe!


- AC Compressor Relay; This is a signal that tells the computer to increase engine idle speed when the AC Compressor Clutch is activated. A failure here would result in stalling when idling with the air on. This is a “probably not”.

- Fuel Pump Relay; This turns the fuel pump on and off. The results of a failure here is obvious, the engine won’t run. List this as a “maybe”.


- VSS (Vehicle Speed Sensor); This is part of the transmission it is a clocking sensor that relays vehicle speed data to the computer, cruise control, and speedometer. A failure here would stop the engine, shut off the speedometer and the cruise control. I give this, or something in this functional circuit, a “highly probable” since it fits most of your symptoms.

- Throttle Position Sensor; A failure here will cause the fuel map to be incorrect to engine load it could result in herky-jerky running to simply stopping the engine. Give this a “maybe”.

- MAP (Manifold Absolute Pressure) Sensor; If this craps out the car reacts from herky-jerky to dead. This and the TPS above are fundamental for the computer to locate engine load fuel and ignition timing needs from the fuel and ignition maps. I’d put his on the “maybe” list.


- 5 Volt Reference. This gem runs every where, it is a basic reference voltage for all things electronic. A failure here would cause the wrong, or a lack of, a reference voltage for some or all engine sensors and the computer. Obviously it would stop the car. This is the kind of thing that could be a wire or connector problem affecting one or more of the sensors or computer. This is also a “maybe” perhaps even a high maybe.

- Bank 1 O2 Sensor; Of course here’s the
obvious as this is the trouble code the
computer is showing. But a failure of the oxygen sensor won’t stop the car and
certainly won’t mess with the speedometer. Gas mileage will go south, that’s about all you’d ever see. Replacing the sensor will cause you to mess with some of the wiring which is where the real problem could be hiding. If a poor connection was re-established as a result of changing the sensor, it could end up looking like the O2 sensor was the problem when in fact it wasn’t.

The “maybes” can add up to a probable, especially if there’s more than one going on at the same time. You have to consider that the fault can be in a wire or connector as well as the more easily replaced but expensive sensor. Each of the sensors have specific test procedures to check them for “goodness”. Obviously the best time to test is when the failure is occurring, otherwise you’re stuck with what I did here, which is to go thru the system logic to try and find which failure mode fits the symptoms. The real headache is when several things are having problems and when they get together you have a total failure but any one of them having a failure doesn’t stop the car. Again you can’t ignore the possibility of a burnt or broken wire, or a connector that’s corroded, damaged, or simply doesn’t make a good connection. But from here, the VSS or someting in its wiring looks most likely as it fits the total failure mode pretty well.

I hope this gives you some ideas of where to go look against that P0420 code. There  might be more, I didn’t put the time into this to go beyond the obvious candidates.

Bogie