Chevrolet Repair: 350 full size blazer wont start, vacuum leaks, flood mode

Question
I have a 350 blazer. Will not start unless you put the pedal to the floor. Was back firing thru throttle body and exhaust. when you let your foot off the cas it won't idle and stalls. I have changed the fuel pump, cleaned out the IAC, TBS tested good, the MAP tested good. The blazer is not tripping any codes at the present time. Any help woudl be useful. I think I have exhausted every option that I know of. Almost ready to throw in new engine.

Answer
Hi Dianne,

DO NOT REPLACE THE MOTOR!!!!  I hope I got to you quick enough to stop you.  Replacing the motor is not the answer.  This is not an internal motor issue, but a drivability one.  At worse, you may have to work on the heads.  $500 or less having someone else do it.  

I was looking through the trash can of questions and found yours.  The orginal expert tossed it out.  I am an expert but on vacation.  I sometimes look at the site for fun.  Anyway...

When a motor wont start, except when 'floored', this is clear flood mode.  That means the truck will start without paying attention to the sensors or computer.  It is used to start a motor that is flooded.  

Did you consider the TPS?  Is the throttle body droping too much fuel?  Is the pressure regulator working?  Vacuum leaks?  Compression on cylinders? (looking for bad valves)  Are the plugs good?  Bad plugs can lead to misfire, or rich mixture.  Coolant temp sensor is the choke of today.  Is the coolant up in the radiator?  Is the EGR valve closed?  

Get someone who is good at drivability.  Your local high school may have an auto shop.  The students in there may fix it for free.  

Good luck.

C J S