Ok furnace would start then in seconds go out blower still running the it would reignite the after a few seconds burner goes out again then finally it stays lit. I had the sail switch replaced didn’t ...
Trouble shooting by replacing parts isn't an economical solution but as Old-Biscuit says, test the high temp limit switch or they are about $10 apiece, just replace it.
High temp limit switch is just an on off switch. Connect a meter or test light from the load side to ground and turn the sucker on. If the the voltage drops to zero and the furnace stops running, wala problem solved.