Tons of car problems here :(

Hi I'm hoping someone can help us identify the problem with our car. We've had so much trouble with it in the last 7-8 months and have put hundreds of dollars into it already. It's a 94 Buick Century, a little over 150,000 miles.
Our first set of problems beginning about 7months ago led us to replacing the following parts-
the battery, all spark plugs, coil pack, MAF sensor, brakes, muffler, fuel pump & fuel filter. We've also done an oil change, tried using higher octane gas, added fuel injection cleaner stuff and "stop-leak" transmission stuff.
Thats all I can think of off the top of my head that we've already done, my husband may have done more but he's at work now and I cant ask him.
Some of the things we've done have helped with SOME of the issues we have had. In the beginning we experienced stalling, rough riding & backfiring & sometimes not wanting to start. Once, it backfired so bad that it blew our muffler apart. Then we started having problems with gas mileage, smelling gas inside and outside of the car while it was running, idling rough... revving high then dropping & sputtering. All along the check engine lights, the brake lights, & oil light have been randomly coming on & off. None of them flicker fast or stay on more than a few minutes at a time. For all we have done and replaced, the only thing that has stopped completely is the backfiring. Just to get my husband to & from work & my kids to & from school in ONE DAY we use almost a half a tank of gas. Our most recent new problems are the transmission slipping when we accelerate & high RPMs with a high pitched whining sound. A few weeks ago we started feeling a vibration & hearing a low pitched knocking/clunking sound when we turned to the right (the sound seemed to come from the front of the car on the passenger side). That however, changed a bit this morning... when I was coming back from taking my daughter to school, the clunking sound got much worse and I could hear it whether I was going straight or turning to either side. The car & steering wheel also started shaking violently. This didn't happen the entire time... it' seemed to come at 20 to 30 second intervals & lasted about 10 or 15 seconds each time, then it stalled (which it hasn't done in a few weeks) but then started back up easily. When I got home, turned the engine off & stepped out of the car I could hear a hissing sound from under the hood and I smelled a type of burning smell, but not like rubber burning, it almost had a chemical or maybe sulfuric smell to it and it seemed to be coming from the front passenger side.
We have 4 kids that I have to transport each day after I drive my husband to work and I'm scared to death of getting back in that car to pick my kids up from school today. We're barely scraping by right now and we know it would be best to take it to a shop or just get a new car all together but we can not afford to do either at the moment. ANY ADVICE/INPUT on what the problem might be this time or what we could do to fix it or at least get a little more life out of it would be so very appreciated.
Sorry this was so long, I just wanted to be as thorough as possible to get the best answers.

WOW. Sounds like you have a mess there. You will need to have the car scanned for codes, for starters.

For the clunk/vibration noise, you may have a C/V joint/ axle assy worn or a bad hub bearing.

Trans sounds like it's low on fluid, check fluid level and check for trans leaks

Hissing sounds like a coolant leak. Could be water pump, hose, radiator, ect... If you don't have a pressure tester, start the car and look around these areas for a leak. Parts stores sell pressure testers for your cooling system.

Hope this helps!

Hi and welcome to the forum!

Just like gmtech1 said the clunking sound or vibration can be caused by worn front end components. Most tire shops can inspect these components for free. It would be a good idea to do so. Try to get the codes read; most autoparts stores will also do it for free. There might be some codes stored in the computer.

You've been given good advice about the transmission, make sure is at the correct level and if the fluid hasn't been changed in a long time it would be a good idea to do so. The transmission filter might be clogging. A violent shuddering when accelerating might also be caused by a bad torque converter which is located between the engine and the transmission. A bad torque converter can also cause the engine to stall when coming to a stop, in such case you should feel a sudden push from behind.

The hissing noise might also be accompanied with a "flowing water" sound and that could indicate a problem with the EVAP system. It helps to keep the gasoline fumes from venting into the atmosphere and improve fuel economy. A damaged hose or charcoal canister will surely cause a fuel smell after turning the engine off but if the problem is bad enough it could also cause it while driving. If you can see no visible fuel leaks under the car or at the engine I would suspect a problem with the EVAP system, specially since you mention the smell being more noticeable at the front passenger side. If I remember correctly, this is where the charcoal canister is located. Look under the hood just behind the passenger headlight, you should see a "plastic can" with some hoses on top of it and an electrical connector. Make sure everything is OK.

A blinking Check Engine Light normally indicates a misfiring problem. you mention you have replace spark plugs and coils but say nothing about spark plug wires. Even when you say the light does not blinks; If they haven't been replaced, it would be a good idea to replace them too.

Those "crazy" lights coming on and off might also be an indicator of a problem with the computer; As long as I can remember it was located behind the glovebox compartment in our 1992 Century. A leak in the windshield could have developed and water is dripping on the computer. You might want to take a look just to make sure. You can follow the wiring and also make sure everything is OK and it's not rubbing against engine components as that might also cause the burning smell and LOTS of problems with sensors.

So far that's all I can think of. I hope it helps.

Oscar.