i have 2003 blazer xtreme 4.3 vortec im having issue where i give it gas it will stall out and die i have replaced distributor and cap replaced the spark plugs replaced air filter replaced coil and replaced maf sensor i was thinking bout the throttle position sensor but wouldnt it throw code for that any help would b appreciated thank you can post pics or vids if need

 

This can be many different things. The best way to approach this is with proper diagnosis so we don't just throw parts at it.

1) How does it idle?
2) Any codes?
3) You need do do the fuel pressure test in the sticky. If OK, look at FP when it stumbles.
4) Do you have a scanner with live data capability? If so then the first thing would be the TPS. key on engine off, look at the values moving the throttle back and forth through full range and look for proper values at the endpoints and no glitches.
5) If all the above is OK then we move on to other things

George

 

had it scanned and only codes it throws is 3 codes for evap i do have the charcoal canister undone because i couldnt pump no gas and the auto store said that wouldnt effect anything and its been undone for couple years now and it idles fine i had mechanic hook fuel pressure gauge up to fuel line and they said it was all fine so yeah i just been throwing parts at it i have scanner but just cheap one that runs off apps on the phone buddy told me to cut the cat off and see if that helps but thanks for the reply gonna try to look at it this weekend sometime

 

I agree, evap related codes have nothing to do with this unless the purge valve is causing a vacuum leak.


The best way is to do proper diagnostics so we know what’s wrong and what to replace or fix. We can get you set up with a low cost solution for scanner capability if you want to go that route. If not then there is quite a list to pick from for throwing parts at the problem:

TPS
O2 sensors
MAF
Fuel pump, regulator, injectors
Cat
Vacuum leak
Ignition coil
ICM
Plugs, wires, distr cap, rotor
Timing
EGR
Other sensors:ECT, MAP, etc

Besides picking from this list, Here are some things you can try to narrow it down:

Look for and fix any vacuum leaks

Pull an Upstream O2 sensor and see if it gets better to check the cat

unplug the MAF sensor and start the truck.

If it does this when cold then it’s probably not the O2 sensors

Clean the EGR valve if equipped

Clean the throttle body

Mist the ignition parts in the dark and look for arching

Do tune up parts: plugs, wires, distr cap, rotor


Let me know if I can help with any of this. Good luck,



George

 

doesnt have egr valve i have changed the maf sensor and the plugs and the distributor and cap and rotor have not done the wires yet because havent seen any sparks at night or anything under hood and they not brittle was thinking throttle position sensor but figured it would of threw code when had it scanned same with the 02 sensors and didnt see any vaccuum lines undone anywhere does it matter what upstream 02 sensor i pull to check cat buddy told me i should have 3 02 sensors 2 upstream and 1 downstream unless he wrong lol its weird when push gas pedal it stalls out and dies but if let off the gas pedal quick enough it will kick back in b4 dieing can let it idle down road and does fine but just cant touch gas

 

Keep in mind that sometimes it’s say the MAF sensor and sometimes it’s the MAF sensor wiring, connectors, voltages so changing a component without testing first could fix the problem with the MAF sensor and it’s circuits but maybe not. This is true of all sensors, especially if they have a 5v or 12v reference circuit.

The best test for the cat causing a loss of power is a back pressure gauge screwed into an up stream O2 sensor port. Removing both upstream sensors should let the engine run better if the cat is plugged. Removing one sensor should show some improvement. Yes you have two upstream and one downstream O2 sensors.

Looking for vacuum hose leaks is a start but there are other hidden sources of vacuum leaks like the reservoir in the fender well or the hoses going to the hvac controller. Fuel trims can help confirm.

The lack of a code does not rule out that item. Fuel trims set a code after a certain set of conditions and trims over 25. The truck can run like absolute crap way before that. Same with O2 sensors, TPS, etc. You can watch the TPS sensor output in live data to make sure it’s proper output from idle to wot and smooth with no glitches through the range.


George

 

I forgot to mention one other low tech possibility - contaminated fuel.

George