98 Chevy Blazer

[NinaV81]

My chevy blazer has 150k mils on it. I started about 6 months ago having problems changing gears so i thought. I was losing power and notice that my cat was clogged. I then went to a muffler shop and put in a straight pipe , w/o the O2 sensor. Since, then I have been experiencing problems with my gas system. I have change the sending unit twice, my fuel gauge doesn't work. and the car will only give me about 80 miles per tank. When my fuel gauge was working the car would not ignite when the level had reached half a tank. It also sputters while driving, and loses power. I am at a loss of words at what can be happening. It's receiving proper pressure, and car only ignites properly with a full tank of gas but only last for 20 miles or less. After that it takes it a while for the car to ignite PLEASE HELP. I have taken it to a few mechanics and no one has a clue.

[Ridenour]

Welcome to the forum. First of all, I suggest you make a thread in the Chevrolet / Blazer forum. This is the wrong (Grand Am) forum. Aside from all your individual symptoms, I would say a huge cause of all this is the fact that your 02 sensor is getting a false reading or whatever from not having a cat / not having an 02 sensor, or whatever your situation is. I would reccomend getting either a stock cat, or an aftermarket one, and reinstalling your post-cat 02 sensor.

[ctesla]

Originally Posted by NinaV81

My chevy blazer has 150k mils on it. I started about 6 months ago having problems changing gears so i thought. I was losing power and notice that my cat was clogged. I then went to a muffler shop and put in a straight pipe , w/o the O2 sensor. Since, then I have been experiencing problems with my gas system. I have change the sending unit twice, my fuel gauge doesn't work. and the car will only give me about 80 miles per tank. When my fuel gauge was working the car would not ignite when the level had reached half a tank. It also sputters while driving, and loses power. I am at a loss of words at what can be happening. It's receiving proper pressure, and car only ignites properly with a full tank of gas but only last for 20 miles or less. After that it takes it a while for the car to ignite PLEASE HELP. I have taken it to a few mechanics and no one has a clue.

Nina,
welcome to AF.
and you should probably PrivateMessage, GTP Dad, and ask him to forward, or re-post this in Blazer; but at least you landed here with other GM folk, it could've been worse.
it does sound like your '98 is looking for feedback from a non-existant O2 sensor, and this could cause idle, driveability problems.
when you say 80 miles to the tank, you ARE talking about the sending unit, or gauge right? not 80miles per 16gallon tank? I'd start walking!
I have never heard of exhaust affecting fuel, but there again, you went to this garage in Florida, and a mechanic (instead of selling you an aftermarket/universal cat, or a direct fit, for more money) knowingly tampered with an EPA federal regulated emission device??? that, by definition is a criminal.
are you sure he didn't need your fuel tank and sender for his full size Silverado? HA.
anyway, I would do as Ridenour suggested, and get a universal cat, and re-plug in (you may have to get a "bung") the O2, or weld in a new threaded piece(a bung) that will allow a sensor to be mounted post cat.
AT THE MINIMUM, get a rear O2 in the pipe downstream somewhere between the piece of straight pipe, and the muffler, and see if this helps.
as far as the fuel, you've replaced sending units twice, I would see if the gauge on the dash possibly has a loose ground (which is definitely possible, since you didn't say anything in your post about an engine light, the mechanic, probably pulled the dash, to pull the bulb) just a thought.
...also, at 150+K miles, have you done a good tune-up lately? idle problems could be electrical ignition components going bad.
hope this helps,
chris
nrt racing