92 olds cutlass backfire

I recently replaced the muffler and catalytic converter on my 92 olds cutlass ciera. One morning a couple days prior to the work, my car began to back fire and started getting horrible gas mileage. I went from getting nearly 400 miles to a tank down to around 200 miles per tank. There is also the faint smell of plastic or rubber burning upon parking and some gasoline smell occasionally.

The car does seem to run better when it is cold out. When I step on the gas to move from a stand still, the car will backfire and shudder. It usually only does it at low speeds (under 40 mph), but also shudders at higher speeds (around 65).

 

I had an Astro that acted like that. One problem was fuel pump the other was plug wires. It had about 150,000 miles. Have a good one. Geo

 

You may wanna look at the ignition coil or coil pack, make sure its not breaking down or improperly grounded. Smell may be from the connection wires arcing...you don't want this to go on too long all that extra gas will damage your new convertor.

 

This has nothing to do with your new exhaust system. It is either in the fuel or ignition system.

 

Which way is it backfiring? Out through the exhaust or back through the intake?

 

backfiring near the engine, not exhaust

complete tune up done, nothing wrong with spark plugs/wires

 

just really need to know if worth fixing or just getting rid of car

 

If an engine backfires out the exhaust it usually means a too rich mixture cause the gas will continue to burn, if the backfire comes back up the intake it usually means too lean a mixture the the fresh gas coming in will ignite with the air left over after lean combustion. Check for vacuum leaks on all vacuum hoses and around the intake manifold and carb or throttle body base gasket. Anything that allows more air in...