4.3L V6 Vortec FI with "W" backfire

94 s-10 blazer 4X4 the tahoe LT package i think 257,000miles, good tires all way round, should get alignment got a slight toe out on her, just cleaned EGR valve and intake plenum of carbon build up the hole leading to EGR valve was completely closed off do to carbon used a screwdriver to clear it best i could, starts right up now doesnt hesitate on start now, usually took a minute or two and constant foot on gas pedal to start, problem is , while driving usualy higher speeds @ and above 30 it would backfire , but not run any diff. thought it was a exhaust leak but cannt finnd a hole anywhere, checked vacuum lines if there was a leak and there isnt, replaced intake plenum gasket and egr valve gasket with the clean screen all after this started, , could it be a sensor maybe, check engine used to come on alot but replaced the box filter with the cone filters and it cured that problem was backfireing before and after replacing filter need a any more info let me know, also replaced about 3-5000 miles ago , fuel tank, sending unit, pump, could not get filter, lines rusted around filter, could snap if tried to take it off, brake lines in rear all replaced, very hard brake pedal with a air sound behind dash where brake booster is not sure if its shot or not, very hard pedal tho, any ideas, cannt bleed brakes bleeders are rusted, one line goin into rear drum is rusted in and strippedcannt bleed that one, bleed only one, ok thats all for now any ideas please let me know

check your exaust welds for the leak ...have you had someone put a timing light on it to see if its slightly out of time...my mom had a 85 Jeep cherokee that would backfire and it was caused by the steering coloum.....let me no if this is any help

Is the Check Engine light on?

Is the backfire only when you let up on gas?
Un burnt fuel or leak in exhaust system is the leading cause of back fire.

Is the backfire only when you let up on gas?
Un burnt fuel or leak in exhaust system is the leading cause of back fire.




yeah sometimes when i let up it back fires, most of the time its when im cruisin with no foot on gas down a hill

Is the Check Engine light on?



been about a month since it came on, last week it came on but it goes off about 3 car starts later, traveling long periods of time at a high speed will cause it to come on also

Does it have a air pump on it.

Most backfire when coasting is exhayst leak.
Some time a air pump can over do the air in exhaust thing.
Is engine running good or running rich or missing?
Check the codes when check engine light comes back on and post back code/codes.
MT