I have a 2003 Chevy Tahoe LT with a 5.3L v8 flex fuel Vortec engine with 192,00 miles on it. OBD 2 codes po171,po174. When accelerating there is a delay before it jumps and starts moving, this is from a full stop. Also when the vehicle gets below a half tank of gas, just above 1/4 tank the vehicle will lose all power while driving at highway speeds, rough idle and then die, it take several tries to get it started without it idling rough and dying. It’ll then drive fine for a few more miles usually till I get it to the gas station and and can fill it up, then the problem goes away, with this issue I’ve noticed the my fuel mileage has gone down drastically as well. I’ve replaced several parts and still have the issue, the parts I’ve replaced are as follows— fuel pump, purge valve and purge valve solenoid, carbon vent canister, fuel filter, All the sensors for the intake, new air filter, and the throttle body w/ throttle position sensor, and I performed an intake leak test. I’m still having this issue and need some help figuring it out. My current thoughts are that it could be the either an issue with the fuel injectors, fuel pressure regulator, or the fuel pressure sensor. I’m doing the work myself from home on a budget and don’t want to keep throwing parts at it hoping I fix the issue, please help me figure this out as I’m basically out of ideas. {black}:bruise:
Another thing to check would be the fuel pressure at the fuel rail, that would give you a better indication of fuel injector problems or lack of fuel pressure caused by something else. I realize you replaced the fuel pump so that should be good but it could be a bad pressure regulator or an internal leak with something inside the fuel tank. Your new fuel pump could be supplying pressure but a ruptured line inside the tank may cause the pressure to drop.
You should be able to rent a fuel pressure gauge that you can connect to the fuel system in the engine bay at an auto parts store. Do a running psi check, make sure your pressure is where it should be, then turn the engine off with the gauge still connected to check for fuel injector leak down. The system should hold pressure for 10 minutes or so when the injectors close. The pressure will drop a few psi initially when the engine stops, after that it should stabilize and maintain pressure for 10 minutes. If you have a continual drop, especially going all the way down to zero, it could be clogged injectors.
Once you know your fuel pressure at the engine you will be able to eliminate many fuel issues.
Thank you, I’ll do that test and see what it does, I don’t think the injectors have ever been cleaned or replaced, so that’s why I think that might be the goblin in my system, I also traced and checked all my fuel lines and vacuum lines and no leaks or issues as far as I can tell, I’ll let you know how the test goes! Since the injectors are probably stock do you think I should just replace them instead of trying to clean them?
Also all the fuel lines on the tank are external, it has an in tank fuel pump, with the lines coming out the top of the pump, the lines are a special kind to handle the E85 flex fuel, and the two lines that on the fuel pump are metal, so no ruptured lines.
Fuel injectors can be expensive so it depends on how much you want to spend, that will help determine if you want to replace them or not. You could try a cleaning with a mechanic that has a tool to connect directly to the fuel rail. The tool injects pressurized cleaning fluid through the injectors while the engine is running. Another option would be to take them off and have a shop clean them off the truck, they will also check the spray pattern, this may cost around $10 to $20 per injector.
Sometimes it feels better to just buy new and be done with it. If you want to do that, go ahead, then you know they are good if you buy good injectors. My problem is, when I do that, sometimes the expensive part doesn't fix the problem.
Did you also replace the MAF sensor with the OEM one?
I replaced all parts with brand new gm oem parts🤷🏻♂️
Sorry for not posting sooner but I did end up replacing the fuel injectors but now I am having an issue with the throttle position sensor not communicating correctly with the pcm and I’m not sure what in the world to do with it, the tps and peddle position sensor are brand new and I replaced the plug for the tps because the wires at the back for the plug were pretty messed up and I didn’t trust it had a proper connection, I don’t have a meter and can’t test the wires for proper voltage and or resistance, any suggestions I’m kinda running out of ideas without taking this thing into the dealer and having them test it and reprogram the ecm 🤷🏻♂️
get a meter. they're only $10. Test lights are even cheaper.
Check your fuel alcohol content
https://carkiller.com/scottykilmer/qa/2008-silverado-flex-fuel-cat-replacement/
https://carkiller.com/scottykilmer/qa/2013-chevy-express-travel-van-obd2-code-running-rich/
