Engine performance

Question by markyD posted 2 weeks 3 days ago in Suburban

On my 94 suburban 1500 4x4 w 5.7 auto the fuelpump /filter &relay were changed afterwards it ran great for a couple weeks then it developed a crank no start problem where it would start when it felt like it and once started would run good shut off and restart fine for a day or two then go back to not starting. Have since changed sparkplugs,dist cap,rotor,wires,piickup coil,ignition module and finally the e.c.m. now it will start all the time but runs horrible idles fluctuates it pops and backfires dies when stopping annd the tach sometimes bounces all over. It seems to missfire erateclly but runs ok under throttleor power any ideas as to what could be the cause ive checked and tested the wireing harness sencers switchs. Everything still does this HELP