First off, I'm glad I found this website as it seems like a great resource for Firebird owners. There's a lot of useful information and resources that should come in handy. Now on to the problem:

Yesterday, I took my Formula over to a friends house to look at. I've been getting bad gas mileage for a while, usually about 13 mpg. A couple of weeks ago, I started getting some nasty rattling and thought it was the catalyst in one of my cats. Sometimes it would be worse, and other times, amost non-existent. Over the last few weeks, it seems like the sound is less of a problem. We looked at it, and I guess there are crack(s) in the exhaust piping between the manifold and the cats - close to, or just in front of the cats. He also thinks my O2 sensor(s) may be bad as I've been getting such bad gas mileage (I have not been driving it even close to hard).

Moving on. I was driving home yesterday on the highway from his place, doing about 75 mph, and I went to give it some gas and nothing seemed to happen. I started slowing down to about 55-60 and got the same effect when I tried to accelerate. So I pulled over, and the idle was all erratic and then it died out. I waited a few, started it back up, and was able to drive, but it still seemed heavily underpowered and response was sluggish. I could rev the engine in neutral, but it still felt sluggish. It stayed roughly the same the rest of the way home. I had no drop in oil pressure, and the engine was not overheating.

Today, I started her up and took her for a spin. Performance seemed normal while it was warming up, and even initially seemed ok when it was entering the operating range and I gave it some gas. After a minute or two though, it relapsed into the same problem as yesterday.

I'm basically wondering if it sounds like this could all be exhaust related. I'm not a mechanic and don't do my own work (usually), but if I have bad O2 sensors that are throwing off my air/fuel mixture, and then a crack in front of the cat that is throwing the pressure in the exhaust system way off, could that be the cause of the problem? Forgive the novel, as I'm just trying to be descriptive, and thanks for any help/opinions/recommendations.

 

it sounds like you could have a bad cat. you said you heard something rattling around in the exhaust near the converter, that could be the stuff inside the cat that has broken up and clogged the pipe. that could be whats giving your power lose. had this happen to me one time. hope this helps.

 

I agree. The rattling is most probably your cat. I have a dual cat system and the factory cats, or least one started rattling and plugging up on me around 107,000. Sometimes the inside of the cat will not rattle but it does come back. Plus you definitely know when it gets plugged. The exhaust sounds muffled and power drops dramatically. If you have a single cat then it would probably explain the gas mileage also. However depending on the mileage of your car, putting in a new oxygen is a cheap maintenance item. They're constantly exposed to high heat and you would think their voltage signal would degrade. Anybody feel welcome to correct me there.

Watch out though for replacement converters. I got a couple from auto zone to weld in and now at 129K I'm getting the same thing. I can get replacements since they'r lifetime but want to get a couple of Random Technologies high flow converters instead. I'm also going to put in a new Bosch 02 sensor for good measure. Trying to see if Auto Zone will give a refund on my current converters. They just want to replace the bad one(s). Would be willing to sell those. Good luck.

 

Sounds good. It's nice to have some people confirming my problem as exhaust related. Thank *** it doesn't appear to be the engine at this point. I think I'm going to look for a high-flow exhaust system w/high flow cats (I have factory dual cats), replace the O2 sensors, put in a 180 degree thermostat, lower temparature fan switch, and I think a new PROM needs to go with that thermostat...hopefully the exhaust system & cats will take care of the major problem.

 

Sounds like a great overall plan. I just put in the 180 degree thermostat when it was time to finally reseal the infamous intake gaskets. It has helped considerably. (160 way too cool for street I think.) Planning on the 200 degree fan switch also. Had slight overheating problems last summer on extremely hot days, on the highway, and running the A/C. Not this year! You can probably get away without changing the prom on a 180 thermostat. I've been running fine a stock EPROM so far. Unless you just want the more aggressive tuning. Going to see how many ponies/torque I can squeeze out of the stock PROM and maintain the 25-26 highway mpg.

Good news. The Auto Zone manager is going to give a full refund on the cats that have gone South already. I better get that in writing!