Alright i have a 92' rs with a 305 only mod is the k&n air filter.
it recently started to backfire everytime i try and drive it down the freeway i can get it up to 45MHP after that it starts to shake really bad and backfires. i already changed the spark plugs i used the E3 also changed the coil the wires and rotor and cap. i dnt know what else to do any help will be greatly appreciated..

 

did you check the timing?

 

was the spark plug gapped correctly? So far you did a partial tuneup. Do a complete tune up and do as gurkgurkgurk posted and check the timing. Tune up:
spark plug/wire, cap/rotor, fuel filter, coil, and timing.

 

most backfiring is due to the timing being excessivly retarded - check it!

finishing your tune-up wouldnt hurt either - the best place to get your timing checked is at a shop that has a scope for your timing and tune-up (it can pinpoint bad wires/plugs/cap/rotor etc...), or use a timing light and vacuum gauge - you're looking for as close to 15 suction as possible, I'm pretty sure the 305 wants the same initial timing as the 350... 10 degrees advanced (BTDC)

 

i have already replaced the everything the only thig i have left is to check the timing.
the E3 plugs i used already came gaped.
would any of the sensors also cause the backfiring??

 

No offence... three people have suggested you check your timing...

Cheers

 

I checked my timing n it is at 6 advanced would the knock sensor cause this??
i ask cause when i looked at it its kinda rusty...

 

6* btdc right?

 

so today on my way to work the car backfires really loud and the engine shuts off and wouldn't go back on when it finally did big chuncks of wut looked like the cat. came flyin out..

 

i took the car in today to get a new cat. and turns out its fine but the muffler was clogged from the previous cat.
so my question is would a clogged exhaust cause any backfiring?