Chevrolet Repair: 97 chevy suburban, throttle position sensor, throttle body injection

Question
QUESTION: "i have a 97 chevy suburban that will not start. it cranks hard but
will not start. i have replaced the fuel filter and tested the fuel pump
but i still get nothing"

ANSWER: Hi David Engle,

You don't start for one of 3 reasons, usually.  1.  no fuel  2.  no spark  3. no/too much air.  Which is your problem?

Is this throttle body injection or port?  In other words, do you have a carbrator looking system?  I believe you do.  Do you see fuel spray there?  Try pushing your gas pedal all the way to the floor, as you turn the key.  

Are you getting spark?  You may have DIS and lots of spark voltage.  Be careful here.  I usually hook up a timing light, crank the motor and look for a signal.  

Today, there are so many variables.  Start with pulling codes.  Crank sensor, map sensor, EGR, ign module, fuel pump pressure regulator, faulty injectors, and on and on.  It starts with determining which of the three needs you don't have.  

When you determine if you don't have gas, air or spark, write me again.  I can help you from there.  Also pull the codes.  Autozone and other auto part places do this for free.  

Good luck in your quest.

C J S

---------- FOLLOW-UP ----------

QUESTION: SINCE I SENT THE PERVIOUS QUESTION I HAVE SINCE REPLACED THE THROTTLE POSITION SENSOR, CAMSHAFT POSITION SENSOR,I AM GETTING FUEL TO THE TOP OF THE MOTOR BUT STILL NOT GETTING FIRE. I TESTED THE SPARK BY TAKING OUT A SPARK PLUG AND LOOKED FOR SPARK WHILE MY WIFE CRANKED IT AND I GOT A SPARK. I AM STUMPED AND EVERYBODY I CALL IS STUMPED. I HAVE TRIED SPRAYING STARTER FLUID IN THE THROTTLE BODY AND IT ATTEMPTS TO START. SOMEBODY TOLD ME TO POUR A LITTLE GAS IN THE THROTTLE BODY SO I TRIED THAT AND IT FIRED OVER LONG ENOUGH TO BURN THE GAS. THANK YOU FOR YOUR HELP

Answer
Hi David Engle,

Of the 3 needs, you are lacking fuel.  Fuel at the top of the motor is not fuel into the motor.  The fact that gas will burn off, once poured down the throttle body, tells us that you have spark, timing, ignition module, sensors, and all related systems...except fuel delivery.  

Here is the system.  Pump to throttle body and back to tank.  Along the way the throttle body sprays a portion of this into the intake.  This amount is set up by computer.  Computer takes in a signal and tells the fuel system what to deliver.  

How did you test your pump.  Does this have a schrader valve for a fuel guage?  Or did you do some sort of 'trick' that someone told you to try.  Chevy is bad about not giving a test port.  Later years they did.  Do you have one?  If so you should see 40 or 50 psi. at cranking.  I know that a pump can seem good, but not be delivering enough fuel pressure.  You get a weak spray, if any at all.  

Fuel pressure regulator is located at the throttle body.  This can go bad and deliver too much back to the tank.  It should work like a small pluggage in the system, so fuel pressure can build up at the injector.  When the injector opens, the fuel will spray out, since it is the path of least resistance.  The pressure regulator is adjustable as needed.  Usually operated by vacuum.  Is the vacuum line here good?  

Is the injector firing at all?  Is any fuel spraying?  You should see a considerable amount of fuel, not just a wimpy spray.  I believe the fuel injectors may have a fuse.  How are the wires here?

Now the hard stuff.  What tells the computer it's signals so it can determine what to tell the fuel system?  Coolant temp sensor is the choke of the old days.  Air charge temp sensor, MAP or MAF sensor, also have roles, but not so big at start-up.  These should put a code.  Check your codes.  

Try these suggestions.  If you still need help from me, write back.  I will go from here.

C J S