5.3 loses power at speed/stalls

[tommyt]

Hi All,
I'm at wits end and in need of help, Have an 2003 Trailblazer LT with a 5.3 liter, 180,000 miles: at high speed engine will dog right down to about 20-30 MPH, give it gas and it sounds like i'm flooding the engine give it light gas and will stay running and sorta coasting for a few miles but will eventually come to a stop, turn it off and in 15 minutes will start back up and run for a little while before it happens again. seems the only constant is the gas is between 1/4 and 1/2 tank. Lasat 2 times this happened i coasted to gas station did not shut it off filled tank and everything was fine till I reached the same gas level of 1/4 to 1/2.
I have replaced TPS and cleaned Throttle body, fuel filter and fuel pressure regulator
Dont know what else to do!

 

[Blckshdw]

Since it seems to be related to the amount of fuel in the tank, the next thing I would look at is the fuel pump. I have never dropped my tank, or seen how things are setup in there, but I'd wonder if there's an issue with wherever the pump picks up the fuel from, is elevated, and no longer at the bottom of the tank?

 

[IllogicTC]

Might be a buildup of sediment in the tank - usually it'd settle at the bottom, but maybe there's something in there that's going to the top, and then coming down over time as the tank is emptied.

Perhaps the fuel pressure in general is starting to get wonky. As odd as this may seem, the fuel in the tank actually helps to keep the fuel pump running cooler. That's part of the reason why people who are constantly running their tanks at 1/8-1/4 (usually because they can't afford more) seem to have their pump go out quicker. You may be having an issue with an intermittently-failing pump that shows up once she gets hot.

 

[tommyt]

Might be a buildup of sediment in the tank - usually it'd settle at the bottom, but maybe there's something in there that's going to the top, and then coming down over time as the tank is emptied.

Perhaps the fuel pressure in general is starting to get wonky. As odd as this may seem, the fuel in the tank actually helps to keep the fuel pump running cooler. That's part of the reason why people who are constantly running their tanks at 1/8-1/4 (usually because they can't afford more) seem to have their pump go out quicker. You may be having an issue with an intermittently-failing pump that shows up once she gets hot.

I also should have mentioned that i can drive around on 1/4 to 1/2 tank city driving with no problem, just on the highway at 50 and above does this happen

 

[Kelly@PCMofNC]

Stick a fuel pressure gauge on her and go for a drive on the highway replicating those conditions to see what you have. Should be 58psi. If it doesn't have fuel pressure and you give it gas, it does feel like what you are describing. Why it does it on the highway and not in the city I do not know, unless the act of city driving (brake, go, brake, go) makes it slosh around and helps it somehow.

Checking fuel pressure is simple (will be a port on the fuel rail) and you can get a gauge that screws on there at Advance Auto for ~$25 or so. Install it and get a long enough hose so that you can run the gauge backwards and tape it to the windshield (or lay it under a wiper). Then you can see it while you are going down the road.

 

[Texan]

I would bet on fuel pump, pressure gauge will tell you the answer.
Does CEL light or REP light ever come on? Any codes set?

 

[strat81]

Hi All,
I'm at wits end and in need of help, Have an 2003 Trailblazer LT with a 5.3 liter, 180,000 miles: at high speed engine will dog right down to about 20-30 MPH, give it gas and it sounds like i'm flooding the engine give it light gas and will stay running and sorta coasting for a few miles but will eventually come to a stop, turn it off and in 15 minutes will start back up and run for a little while before it happens again. seems the only constant is the gas is between 1/4 and 1/2 tank. Lasat 2 times this happened i coasted to gas station did not shut it off filled tank and everything was fine till I reached the same gas level of 1/4 to 1/2.
I have replaced TPS and cleaned Throttle body, fuel filter and fuel pressure regulator
Dont know what else to do!

The symptoms sound very similar to my 5.3 when the fuel pump died. My suspicion is that it was overheating. A full tank of fuel "fixed" the problem but it would act like yours with stalling and such when below a 1/2 tank. The fuel acts as a coolant, thus delaying the stalling.

Since the fuel pump is a royal PITA to replace, you may not want to replace it unless you know for sure that is the problem.

Get a fuel pressure gauge like this:
Actron CP7838 Professional Fuel Pressure Tester : Amazon.com : Automotive

Attach it, then tape it to your windshield. Go for a ride with a friend and have them watch the gauge as you drive.

 

[The_Roadie]

I agree on the fuel delivery system. Otherwise I'd check into a deteriorating air filter that collapses and pinches off the airflow.